Animal Nutrition

Nutrient classes, digestion, feed additives, lipid metabolism, mineral nutrition, vitamins, energy, nutrient calculations, feed analyses, diet formulation, carbohydrates, and amino acids (ANSC 223, Lectures 1–14)

SummaryTLDRLectures 1–14 · Nutrients

1Nutrients

Compound	Function & Activated Forms	Key Sources	Deficiency / Notes
Lipids(Lec 5)
Triacylglycerols (TAGs)	Primary form of dietary fat (>90%); glycerol + 3 esterified FA chains; 9 kcal/g; bile acids (cholesterol-derived) + lecithin (phospholipid) emulsify fat → ↑ surface area for pancreatic lipase → 2-MAG + 2 FFAs → re-esterified in enterocytes → chylomicrons → lymph → blood	Animal fats (lard, tallow, butter), vegetable oils; virtually all dietary fats	Insufficient intake → body fat mobilization → ketosis (dairy cows, ewes) Excess → obesity, hepatic lipidosis (cats); ↑ plasma TAG → pancreatitis risk
Phospholipids	Amphipathic membrane lipids; phosphatidylcholine (most abundant — head group = choline → ↔ choline quasi-vitamin; required for VLDL assembly → hepatic fat export); phosphatidylethanolamine; sphingomyelin (myelin sheaths); VLDL & chylomicron surface monolayer; synthesized endogenously	Egg yolk (lecithin), soybeans, organ meat; endogenous synthesis	Dietary deficiency rare (endogenous synthesis) Impaired VLDL assembly if choline component lacking → hepatic lipidosis
Cholesterol	Membrane fluidity regulator (intercalates between phospholipid fatty acid chains); precursor for steroid hormones (cortisol, estrogen, testosterone), bile acids (emulsify dietary fats → ↔ fat digestion), and Vit D₃; 7-dehydrocholesterol (biosynthetic intermediate) → UV light in skin → cholecalciferol (Vit D₃) → ↔ Vit D; synthesized via mevalonate/HMG-CoA reductase; transported as LDL (delivery to tissues) / HDL (reverse cholesterol transport)	Animal products only (eggs, meat, dairy); endogenous synthesis (liver, intestine)	Dietary deficiency rare (endogenous synthesis); essential for steroid hormone & bile acid production Excess → atherosclerosis in companion animals & humans
Lauric acid (C12:0)SAT	Medium-chain saturated FA; absorbed directly into portal blood (bypasses chylomicron/lymph pathway); antimicrobial — disrupts bacterial & viral lipid envelopes; major FA in coconut & palm kernel oil	Coconut oil (~47%), palm kernel oil, dairy (trace)	Rarely deficient; rapid portal absorption used in MCT supplements for fat malabsorption High intake → ↑ total & LDL cholesterol
Myristic acid (C14:0)SAT	Medium-to-long chain saturated FA; myristoylation — N-terminal co-translational lipid modification anchors proteins (e.g. Src kinases, G-protein α-subunits) to membranes; most potent common dietary SFA for raising LDL:HDL ratio	Coconut oil, palm kernel oil, dairy fat (nutmeg ~75% myristic)	Rarely deficient; excess → ↑ LDL cholesterol more than C16:0 or C18:0
Palmitic acid (C16:0)SAT	Most abundant SFA in animals & plants; major membrane phospholipid component (sn-1 & sn-2 positions); primary de novo synthesis product of FA synthase (FAS); elongated to stearic acid; precursor for sphingolipid ceramide backbone; palmitoylation (reversible protein lipid modification)	Palm oil, animal fat (lard, butter, dairy); de novo synthesis from acetyl-CoA	Rarely deficient (de novo synthesis); excess → membrane rigidity, ↑ LDL
Stearic acid (C18:0)SAT	Long-chain SFA; major product of rumen biohydrogenation — Butyrivibrio fibrisolvens converts dietary PUFA → C18:0 in rumen; elongated from palmitic; desaturated to oleic via Δ9-SCD (stearoyl-CoA desaturase); neutral effect on plasma LDL vs C16:0	Animal fat (beef tallow, cocoa butter); rumen biohydrogenation end-product	Rarely deficient; rumen biohydrogenation of PUFA → ↑ stearic acid in ruminant products
Palmitoleic acid (C16:1 ω-7)cis	Monounsaturated FA; synthesized by Δ9-desaturase (SCD) from palmitic acid; proposed lipokine role — secreted by adipose tissue ('palmitolein') and may signal insulin sensitivity in liver & muscle; abundant in fish & ruminant fat	Fish oil (mackerel, herring), macadamia nuts, ruminant fat; endogenous via SCD	Rarely deficient; low plasma levels associated with insulin resistance in some studies
Oleic acid (C18:1 ω-9)cis	Most abundant MUFA in animal tissues; membrane fluidity; high oxidative stability (fewer double bonds than PUFA → less prone to peroxidation → ↔ Vit E); synthesized by Δ9-SCD from stearic acid; ↑ LDL receptor expression → ↓ LDL; staple of Mediterranean diet; high in olive oil	Olive oil, canola oil, animal fat; endogenous synthesis via Δ9-SCD	Rarely deficient (synthesized from stearic acid via SCD); ↓ SCD activity → stiffer membranes
Vaccenic acid (C18:1 t11)trans	Natural ruminant trans FA; produced by incomplete biohydrogenation of LA/ALA in rumen (Butyrivibrio fibrisolvens); Δ9-SCD in body tissues converts vaccenic acid → CLA (c9,t11) → ↔ CLA (precursor relationship); distinct from industrial trans fats; neutral to beneficial health effects	Dairy fat (~3–5%), ruminant meat fat; natural biohydrogenation product	Not deficient; precursor for endogenous CLA synthesis; considered beneficial unlike industrial trans fats
Elaidic acid (C18:1 ω-9 trans)trans	Industrial trans FA; geometric isomer of oleic acid (same Δ9 double bond position, but trans configuration → straighter chain → disrupts membrane fluidity); formed by partial hydrogenation of vegetable oils; ↑ LDL, ↓ HDL, promotes inflammation; no known metabolic benefit	Partially hydrogenated vegetable oils (margarine, shortening, fried foods); industrial process	↑ LDL & ↓ HDL → ↑ cardiovascular disease risk; pro-inflammatory Banned in many countries; FDA eliminated partially hydrogenated vegetable oils (PHVO) from U.S. food supply
Linoleic acid (LA, 18:2 ω-6)cis	Essential ω-6; both double bonds cis (Δ9cis, Δ12cis); cannot be synthesized by animals; precursor → AA (via Δ6-desaturase → Δ5-desaturase) → pro-inflammatory eicosanoids (PGE₂, TXA₂, LTB₄); required for skin barrier lipid integrity; competes with ALA for Δ6-desaturase (rate-limiting step)	Corn oil, soybean oil, sunflower oil	Poor skin & coat (dry, scaly); impaired skin barrier integrity Impaired reproduction; growth failure
γ-Linolenic acid (GLA, 18:3 ω-6)cis	ω-6 PUFA; all three double bonds cis (Δ6cis, Δ9cis, Δ12cis); produced from LA via Δ6-desaturase (rate-limiting step, shared with ALA pathway) → DGLA (C20:3 ω-6) → competes with AA for COX/LOX; DGLA produces anti-inflammatory PGE₁; anti-inflammatory at pharmacological doses	Evening primrose oil (~9%), borage oil (~20%), black currant seed oil	Rarely deficient normally; ↓ Δ6-desaturase activity (aging, diabetes, trans fats, excess LA) → impaired GLA synthesis
α-Linolenic acid (ALA, 18:3 ω-3)cis	Essential ω-3; all three double bonds cis (Δ9cis, Δ12cis, Δ15cis); precursor → EPA (20:5 ω-3, anti-inflammatory eicosanoids) → DHA (22:6 ω-3, brain/retina); conversion efficiency ~5–15% (limited by shared Δ6-desaturase with LA); high ω-6:ω-3 ratio in diet ↓ ALA conversion	Flaxseed, canola oil, fish	Poor neural development & visual function Reproductive failure; chronic pro-inflammatory state
Conjugated linoleic acid (CLA, 18:2 c9,t11)cis/trans	Positional & geometric isomers of LA; c9,t11-CLA (rumenic acid) most abundant; produced by Butyrivibrio in rumen OR by Δ9-SCD acting on vaccenic acid in body tissues (→ ↔ vaccenic acid); anti-tumorigenic, anti-atherogenic; ↑ lean mass / ↓ body fat in some species; immunomodulatory	Dairy fat & ruminant meat (grass-fed 3–5× higher); ~400–700 mg/day in typical dairy intake	Not a recognized deficiency; high-grain rumen diets → ↓ rumen biohydrogenation pathway → ↓ CLA in milk & meat Grass-fed/pasture ruminants → ↑ vaccenic + CLA content
Arachidonic acid (AA, 20:4 ω-6)cis	All four double bonds cis (Δ5,8,11,14); pro-inflammatory eicosanoids — COX pathway → PGE₂, TXA₂ (platelet aggregation); LOX pathway → LTB₄ (neutrophil chemotaxis); derived from LA via Δ6-desaturase (shared rate-limiting step with ALA) + Δ5-desaturase; cats & ferrets: insufficient Δ6-desaturase activity → dietary AA essential	Animal tissue (liver, eggs)	Cats/ferrets: reproductive failure, poor coat Hepatic lipidosis (cats on AA-deficient diets)
EPA (20:5 ω-3) & DHA (22:6 ω-3)cis	All double bonds cis; EPA (Δ5,8,11,14,17) → anti-inflammatory eicosanoids (PGE₃, LTB₅ — compete with AA-derived eicosanoids); DHA (Δ4,7,10,13,16,19) → brain & retinal membrane structure (high in photoreceptor outer segments); both derived from ALA (rate-limited by Δ6-desaturase → ↔ LA competes); ↓ platelet aggregation & plasma TAG; fish obtain EPA/DHA from marine algae	Fish oil, marine algae	Chronic inflammation (excess ω-6:ω-3 ratio → ↑ AA-derived eicosanoids) Poor neural & visual development (neonates)
Feed Additives(Lec 4)
Monensin (ionophore)	Disrupts Na⁺/H⁺ gradient in gram⁺ rumen bacteria → ↑ propionate, ↓ acetate & methane; ~5–10% ↑ feed efficiency; ~80% ionophore market share	Synthetic (ruminant feed additive only)	FATAL to horses — extremely cardiotoxic; never use in equine Prevents bloat & SARA at therapeutic doses Overdose → cardiac myopathy in cattle
Ractopamine (β-agonist)	β₂-adrenergic agonist → redirects nutrients from fat deposition to lean muscle; Paylean (swine), Optaflexx (cattle); fed last 28 days; no withdrawal period required	Synthetic	Banned in EU, China, Russia; approved USA/Canada Can cause stress-related behavioral changes in swine at higher doses
Phytase	Hydrolyzes phytate (plant P storage) → releases inorganic P; ↑ P bioavailability 50–75% in monogastrics; ↓ fecal P excretion; also releases Ca, Zn, Fe bound to phytate	Microbial enzyme supplement (Aspergillus niger, E. coli phytase)	Without phytase: low P bioavailability in monogastrics Excess fecal P → water eutrophication (environmental impact)
Poloxalene (Bloat Guard)	Non-ionic surfactant breaks frothy foam in rumen; restores eructation; for frothy (primary) legume bloat only — does NOT prevent free-gas (secondary) bloat	Synthetic (lick block, feed mix formulation)	Without treatment: fatal tympanic bloat Does not prevent free-gas bloat (requires passage tube or trocar)
Probiotics	Live beneficial microbes (Lactobacillus, Bifidobacterium, Saccharomyces, Aspergillus); establish healthy GI microbiome; most effective in young, stressed, or antibiotic-treated animals	Fermented feed, commercial supplements	Dysbiosis (stress, weaning, antibiotics) → diarrhea, poor growth Reduced benefit if gut microbiome already well-established
MacroMinerals(Lec 6)
Calcium (Ca)	Bone/teeth as hydroxyapatite [Ca₁₀(PO₄)₆(OH)₂]; muscle contraction (troponin C); nerve signaling; blood clotting (cofactor for thrombin); Ca:P ratio 1.5–2:1 optimal; ↔ Vit D: calcitriol (1,25-(OH)₂D₃) → ↑ calbindin D (intestinal Ca-binding protein) → ↑ Ca absorption; ↔ PTH: ↓ Ca → ↑ PTH → ↑ bone resorption + ↑ 1α-hydroxylase → ↑ calcitriol; prepartum DCAD↓ → metabolic acidosis → ↑ PTH receptor sensitivity → ↑ Ca mobilization at calving → ↓ milk fever	Limestone (CaCO₃), alfalfa hay, dairy products	Milk fever — periparturient hypocalcemia; muscle weakness, recumbency Rickets — young; soft, deformed long bones Osteomalacia — adult; demineralized, fragile bones
Phosphorus (P)	Bone/teeth (80% as hydroxyapatite); ATP backbone (energy currency); DNA/RNA backbone; phospholipid membranes; signaling (cAMP, IP₃, protein phosphorylation); Ca:P ratio 1.5–2:1 (imbalance → impaired bone despite adequate absolute amounts); ↔ Vit D: calcitriol ↑ intestinal P absorption via NaPi transporters; phytate-bound P = 60–80% of total P in grains — unavailable to monogastrics without phytase → ↔ phytase (enzyme supplement)	Dicalcium phosphate, grains, meat meal	Pica — eating non-food items (dirt, bones, wood); sign of P or mineral deficiency Poor bone density; reduced reproductive performance
Potassium (K)	Primary intracellular cation (~98% intracellular); Na⁺/K⁺-ATPase (maintains resting membrane potential); osmotic balance; nerve & muscle action potentials; DCAD; ↔ Mg: excess K⁺ in lush spring grass competes with Mg²⁺ at rumen epithelial & intestinal transporters → ↓ Mg absorption → grass tetany risk	Alfalfa, green forage, molasses	Deficiency: weakness, cardiac arrhythmia, ↓ feed intake Excess K ↓ Mg absorption → ↑ grass tetany risk in lactating cows
Sodium (Na)	Primary extracellular cation; osmotic balance of body fluids; only mineral with 'nutritional wisdom' (salt-seeking behavior when deficient); Na⁺/K⁺-ATPase; DCAD; drives secondary active transport (SGLT1 for glucose, amino acid co-transporters)	NaCl (table salt), mineral blocks	Salt craving, pica; reduced milk production Weight loss, weakness, heat stress susceptibility
Chlorine (Cl)	HCl in stomach (gastric acid, activates pepsinogen → pepsin); DCAD = (Na + K) − (Cl + S); anionic salt supplementation prepartum (CaCl₂, MgCl₂, CaSO₄) → ↓ blood pH → metabolic acidosis → ↑ PTH receptor upregulation → ↑ Ca mobilization efficiency → ↓ milk fever; ↔ Ca (DCAD manipulation)	NaCl, anionic salt supplements (prepartum cow diets)	Deficiency: metabolic alkalosis (purified diet scenarios) Low DCAD prepartum → ↑ Ca mobilization at calving → ↓ milk fever
Sulfur (S)	Structural component of Met, Cys, taurine (amino acids → ↔ protein quality); also of thiamine B1 (thiazole ring) & biotin B7 (tetrahydrothiophene ring → ↔ vitamins); wool/hair keratin via Cys–Cys disulfide bonds; N:S = 10:1 in ruminants for optimal microbial protein synthesis; ↔ B1 (thiamine): excess S → rumen microbes produce H₂S → inhibits pyruvate dehydrogenase (same TPP-dependent enzyme) → functional thiamine-equivalent deficiency even with adequate B1 → polioencephalomalacia	Protein feeds, elemental S (ruminant supplementation)	Deficiency: poor wool/hair growth; ↓ rumen microbial protein synthesis Excess: rumen H₂S → polioencephalomalacia (thiamine destruction/interference)
Magnesium (Mg)	Cofactor for ALL ATP-dependent enzymes (>300 kinases, ATPases, synthetases — Mg²⁺-ATP is the true substrate); 60–70% in bone; core of plant chlorophyll; Mg²⁺ counterion in DNA/RNA double helix; ↔ K: high K⁺ in spring grass inhibits trans-epithelial Mg²⁺ transport (rumen wall, intestine) → ↓ Mg absorption; only ~20% dietary Mg absorbed; loss in milk accelerates depletion in lactating cows	MgO supplement, green forage (bioavailability ↓ by high K⁺ and NH₄⁺)	Grass tetany (hypomagnesemia) — nervousness, tremors, convulsions, death Mainly lactating cows on lush spring pasture; high K in spring grass reduces Mg absorption
Microminerals(Lec 7)
Iron (Fe)	Hemoglobin (O₂ transport, heme Fe²⁺); myoglobin (O₂ storage in muscle); cytochromes ETC (Fe²⁺↔Fe³⁺ redox); ferritin/hemosiderin (storage); transferrin (transport, Fe³⁺); ↔ Cu: ceruloplasmin (Cu-dependent ferroxidase) converts Fe²⁺→Fe³⁺ for loading onto transferrin after exit from enterocytes via ferroportin — Cu deficiency → Fe accumulates but cannot be transported → functional anemia; ↔ Vit C: ascorbate reduces gut Fe³⁺→Fe²⁺ → ↑ non-heme Fe absorption via DMT1; hepcidin (liver peptide hormone) suppresses ferroportin → regulates systemic Fe homeostasis	Liver, meat; iron dextran injection (neonatal piglets)	Baby pig anemia — pale mucous membranes, weakness, death; sow milk very low in Fe General iron-deficiency anemia in other species; ↓ cytochrome activity → impaired oxidative metabolism
Selenium (Se)	Selenoprotein component: glutathione peroxidase (GPx₁–₄) reduces H₂O₂ & lipid hydroperoxides using GSH as electron donor — acts in aqueous compartments (cytoplasm, mitochondria); ↔ Vit E: α-tocopherol interrupts lipid peroxyl radical chains in membrane lipid phase; Se/GPx and Vit E are complementary (different locations & substrates) and non-interchangeable — deficiency of either cannot be fully compensated by the other; ↔ GSH: GPx requires glutathione (GSH); Se in thioredoxin reductase (TrxR) also; organic selenomethionine > inorganic Se (bioavailability); FDA max 0.3 ppm total Se in feed	Selenium yeast, sodium selenate; forage content soil-dependent	White muscle disease (nutritional myopathy) — calves, lambs, foals; pale striated muscle necrosis Mulberry heart disease — swine; myocardial necrosis Retained placenta; ↑ selenosis risk (hair/hoof loss, blind staggers) above 2–5 ppm
Copper (Cu)	Ceruloplasmin (Cu-ferroxidase: Fe²⁺→Fe³⁺ for transferrin loading → ↔ Fe transport); cytochrome c oxidase (ETC complex IV, terminal O₂ reduction); lysyl oxidase (collagen & elastin crosslinks → ↔ connective tissue strength); tyrosinase (melanin synthesis from Tyr → ↔ Tyr); ↔ Mo & S: high Mo + S in rumen → thiomolybdates (MoS₄²⁻) → bind Cu → ↓ Cu availability (molybdenosis/teart); ↔ Zn: high Zn → ↑ metallothionein in enterocytes → sequesters Cu → secondary Cu deficiency (used therapeutically in Cu toxicosis)	Copper sulfate, liver, oysters	Anemia (Fe transport impaired); depigmentation (↓ melanin, grey coat/hair) Bone fractures (↓ lysyl oxidase → poor collagen crosslinking); Menkes disease (ATP7A, absorption defect); Wilson's disease (ATP7B, Cu accumulation)
Iodine (I)	Thyroid hormone synthesis: I⁻ taken up by NIS (Na/I symporter) → oxidized by TPO (thyroid peroxidase, H₂O₂-dependent) → iodinates Tyr residues on thyroglobulin → MIT (monoiodotyrosine) + DIT (diiodotyrosine) → T₃ (MIT+DIT, 3 I atoms) + T₄ (DIT+DIT, 4 I atoms) — T₃ & T₄ are iodinated Tyr derivatives → ↔ Tyr (structural component); T₃ is the biologically active form (T₄ deiodinated to T₃ in peripheral tissues by deiodinases, which are selenoproteins → ↔ Se); regulate BMR, growth, reproduction; TSH (pituitary) stimulates I uptake and hormone release	Iodized salt, fishmeal, kelp	Goiter — ↓T₃/T₄ → ↑TSH → thyroid gland enlargement Stillbirths; weak/hairless neonates; goitrogens (glucosinolates in brassicas, soy isoflavones) inhibit TPO or NIS → worsen deficiency
Zinc (Zn)	Cofactor for 300+ enzymes (carbonic anhydrase, DNA polymerase, Cu/Zn-SOD, alkaline phosphatase); structural in zinc-finger transcription factors (Cys₂His₂ motif — gene regulation); skin integrity (keratinocyte proliferation), immune function (thymulin, T-cell maturation), wound healing; ↔ Cu: high Zn → ↑ metallothionein (cysteine-rich protein) in enterocytes → Cu sequestered → secondary Cu deficiency (excess Zn used therapeutically against Cu toxicosis); ↔ phytate: phytate chelates Zn²⁺ → ↓ bioavailability (phytase helps)	Zinc oxide/sulfate, animal protein; phytate in grains ↓ bioavailability	Parakeratosis — dry, scaly skin lesions (swine on high-Ca/phytate diet) Poor immunity; ↓ growth rate; delayed wound healing
Manganese (Mn)	MnSOD (mitochondrial matrix antioxidant — superoxide → H₂O₂); bone development (Mn-dependent glycosyltransferases synthesize proteoglycan/cartilage matrix → ↔ bone structure); reproduction; arginase (urea cycle: Arg → ornithine + urea, requires Mn²⁺); ↔ Ca, Fe: high Ca and Fe compete with Mn for intestinal absorption → ↓ Mn bioavailability	Forages, Mn sulfate/oxide supplement	Perosis (slipped tendon) — poultry; enlarged, rotated hock joint (also requires adequate choline and biotin) Poor bone formation; reproductive failure; MnSOD ↓ → mitochondrial oxidative stress
Cobalt (Co)	Co is the central metal ion of cobalamin's corrin ring; rumen bacteria incorporate dietary Co → synthesize Vit B₁₂; ↔ B12: Co → B12 → (1) methylmalonyl-CoA mutase (propionate → succinyl-CoA, major gluconeogenic step in ruminants) + (2) methionine synthase (homocysteine → Met, with folate/B9); monogastrics cannot synthesize B12 from dietary Co — must receive preformed B12; Co deficiency in ruminants ≡ B12 deficiency	Cobalt sulfate/carbonate supplement; rumen microbial synthesis	Pine disease / wasting (ruminants) — B₁₂ deficiency → failed propionate utilization → wasting, anemia Weight loss, poor growth; monogastrics need dietary B₁₂ (not dietary Co)
Fluorine (F)	Replaces –OH in hydroxyapatite → fluorapatite [Ca₁₀(PO₄)₆F₂] in dental enamel (harder crystal lattice, more acid-resistant → ↔ Ca, P: fluorapatite modification); 0.7–1 ppm in drinking water for caries prevention; no established essential metabolic role beyond dental/bone hardening	Fluoridated water, seafood, bone meal	Too low: dental caries (cavities) Fluorosis (excess) — mottled/pitted enamel; osteofluorosis (brittle, deformed bones)
Molybdenum (Mo)	Cofactor for molybdoenzymes: xanthine oxidase (purines → hypoxanthine → xanthine → uric acid), aldehyde oxidase, sulfite oxidase (sulfite → sulfate, detoxification); required in trace amounts; ↔ Cu & S: excess Mo + S in rumen → thiomolybdates (MoS₄²⁻, MoS₃OH⁻) → chelate dietary Cu AND mobilize tissue Cu → secondary Cu deficiency (molybdenosis/teart); thiomolybdate formation requires both excess Mo AND sulfur	Legumes, cereal grains (soil-dependent concentration)	Excess → thiomolybdates bind Cu → secondary Cu deficiency (molybdenosis / teart) Requires excess S for thiomolybdate formation; pure Mo deficiency extremely rare
Fat-Soluble Vitamins(Lec 8)
Vitamin A (retinol)	Visual cycle: 11-cis-retinal + opsin = rhodopsin (rod photoreceptors); all-trans-retinal released on light absorption → signal transduction; epithelial differentiation (retinoic acid → RAR/RXR nuclear receptors → gene transcription for epithelial differentiation, immunity); reproduction (spermatogenesis, embryogenesis); β-carotene → retinol conversion: ruminants moderate, poultry low, cats & dogs cannot convert → need preformed retinol; stored in liver stellate cells (>90% of body stores); ↔ Vit E: tocopherol protects retinol from oxidative destruction during digestion, GI transport & liver storage	Liver, fish liver oil, egg yolk; β-carotene (green/yellow plants, carrots, corn)	Night blindness — earliest sign; reduced rhodopsin regeneration in dim light Hyperkeratosis — hard, rough keratinized epithelium (skin, respiratory, GI mucosa) Reproductive failure; ↑ infection susceptibility; hypervitaminosis A → bone fractures & hepatotoxicity (cats especially)
Vitamin D (D₃ = cholecalciferol)	Synthesis: 7-dehydrocholesterol (cholesterol biosynthetic intermediate → ↔ cholesterol) in skin → UV-B (290–315 nm) photolysis → cholecalciferol (D₃); activation cascade: liver CYP2R1 (25-hydroxylase) → 25-OH-D₃ (calcidiol, blood transport/storage form) → kidney CYP27B1 (1α-hydroxylase, stimulated by ↑PTH, ↓Ca²⁺, ↓Pi) → 1,25-(OH)₂D₃ (calcitriol, active form); calcitriol binds VDR (nuclear receptor) → ↑ calbindin-D (Ca-binding protein) → ↑ intestinal Ca & P absorption; ↑ renal Ca reabsorption; ↑ bone mineralization; ↔ Ca & P: calcitriol drives intestinal Ca & P uptake; ↔ PTH: feedback loop — ↑ calcitriol → ↓ PTH secretion, ↓ 1α-hydroxylase, ↑ 24-hydroxylase (→ inactivation to 24,25-(OH)₂D₃)	Sunlight (UV-B), fish liver oil, sun-cured hay; D₂ (ergocalciferol) from irradiated plant ergosterol	Rickets (young) — soft, deformed, painful long bones; widened growth plates at metaphyses Osteomalacia (adult) — bone demineralization; ↑ fracture risk Toxicity → hypercalcemia → soft-tissue calcification (arteries, kidneys, lungs)
Vitamin E (α-tocopherol)	Chain-breaking antioxidant: α-tocopherol donates H• to lipid peroxyl radicals (LOO•) in PUFA-rich membrane phospholipids → LOO-H + tocopheroxyl radical (stable) → interrupts lipid peroxidation chain; ↔ Se: GPx (selenoprotein) handles H₂O₂ & lipid hydroperoxides in aqueous phase (cytoplasm); Vit E acts in lipid membrane phase — complementary mechanisms, non-interchangeable, both needed; ↔ Vit C: ascorbate (aqueous) reduces tocopheroxyl radical → regenerates α-tocopherol (Vit E recycling at membrane-water interface); ↔ Vit A: protects retinol from oxidative degradation; requirement increases with ↑ dietary PUFA	Green forage, vegetable oils, wheat germ, nuts	White muscle disease (nutritional myopathy) — calves, lambs, foals; pale striated muscle necrosis Mulberry heart disease — swine; myocardial & hepatic necrosis Retained placenta; ↓ immunity; ↑ oxidative stress in muscle (concurrent Se deficiency worsens outcome)
Vitamin K (K₁ phylloquinone; K₂ menaquinone)	γ-Carboxylation of Glu → γ-Gla (γ-carboxyglutamate) residues by GGCX (γ-glutamyl carboxylase): clotting factors II (prothrombin), VII, IX, X + anticoagulant proteins C & S; also osteocalcin (bone Gla protein, bone mineralization) & MGP (inhibits vascular calcification); Vit K cycle: KH₂ (hydroquinone, active donor) → KO (epoxide, spent) → recycled by VKOR (Vit K epoxide reductase); warfarin & dicoumarol (sweet clover mycotoxin) competitively inhibit VKOR → K cannot be recycled → Glu carboxylation fails → non-functional clotting factors → hemorrhage; ↔ Ca: Gla residues in osteocalcin/MGP bind Ca²⁺ for bone & vascular Ca regulation	Green leafy plants (K₁); gut bacterial synthesis (K₂); fermented feeds	Bleeding/clotting disorders; prolonged prothrombin time (PT); ecchymoses Sweet clover poisoning — dicoumarol (anticoagulant mycotoxin from moldy sweet clover hay) → fatal hemorrhage in cattle
Water-Soluble Vitamins(Lec 8)
Thiamine (B1) → TPP	Thiamine pyrophosphate (TPP): cofactor for oxidative decarboxylases — pyruvate dehydrogenase (pyruvate → acetyl-CoA, links glycolysis to TCA), α-ketoglutarate dehydrogenase (TCA), branched-chain α-keto acid dehydrogenase (BCAA catabolism); also transketolase (pentose phosphate pathway); ↔ S: excess dietary S → rumen H₂S → inhibits pyruvate dehydrogenase at same step as TPP → functional thiamine deficiency even if B1 status adequate → polioencephalomalacia; thiaminase (bracken fern, raw fish) directly destroys B1; ruminants synthesize B1 via rumen microbes (vulnerable to S or thiaminase disruption)	Cereal grains, yeast, legumes; rumen microbial synthesis	Polioencephalomalacia (ruminants) — H₂S from high-S diet or thiaminase → cerebrocortical necrosis Beriberi (monogastrics) — wet form (cardiac enlargement, edema) or dry form (peripheral neuropathy) Wernicke's encephalopathy (primates: ataxia, confusion, ophthalmoplegia)
Riboflavin (B2) → FMN, FAD	FMN (flavin mononucleotide) & FAD (flavin adenine dinucleotide): prosthetic groups for flavoproteins; function as 2-electron + 2H⁺ carriers in ETC (Complex I, II), β-oxidation (acyl-CoA dehydrogenase), TCA (succinate dehydrogenase); ↔ B6 & niacin: FMN/FAD are cofactors for pyridoxine 5′-phosphate oxidase (B6 activation) and kynurenine 3-monooxygenase (Trp → niacin) → B2 deficiency impairs B6 and niacin metabolism	Milk, eggs, meat, green plants; gut microbial synthesis in ruminants	Curled-toe paralysis — poultry; peripheral neuropathy, toe curling inward Poor growth; skin lesions (cheilosis = cracked lip corners, glossitis = inflamed tongue); rarely deficient in ruminants
Niacin (B3) → NAD⁺, NADP⁺	NAD⁺ & NADP⁺: major 2H⁻ (hydride) carriers — NAD⁺ in catabolic pathways (glycolysis, TCA, β-oxidation), NADPH in anabolic pathways (FA synthesis, pentose phosphate, antioxidant via glutathione reductase); Trp → niacin via kynurenine pathway (kynureninase step requires PLP/B6 → ↔ B6; kynurenine 3-monooxygenase requires FAD/B2 → ↔ B2); 60 mg Trp = 1 mg niacin; cats: lack hepatic tryptophan 2,3-dioxygenase AND sufficient PLP for conversion → dietary niacin essential	Meat, fish, peanuts, yeast; tryptophan (dietary precursor); ruminant rumen synthesis	Pellagra — 4 Ds: Dermatitis (photosensitive), Diarrhea, Dementia, Death Black tongue — dogs; niacin deficiency equivalent of pellagra Cats cannot convert Trp → niacin; require preformed dietary niacin
Pantothenic acid (B5) → CoA	Structural component of Coenzyme A (CoA) and acyl carrier protein (ACP): CoA activates acyl groups for FA synthesis & β-oxidation (acetyl-CoA, malonyl-CoA, succinyl-CoA) and TCA (acetyl-CoA entry); acetylcholine synthesis (acetyl-CoA + choline, ↔ choline); widely distributed in living cells (pantos = 'everywhere' in Greek); no single major antagonist mineral/vitamin interaction	Widely distributed: liver, eggs, legumes, yeast	Goose-stepping gait (pigs) — spastic hindlimb movement from peripheral neuropathy Poor feathering (poultry); dermatitis; adrenal cortex atrophy; rarely deficient in natural diets
Pyridoxine (B6) → PLP	Pyridoxal phosphate (PLP): cofactor for >100 enzymes primarily in AA metabolism — transamination (AA interconversion: alanine, aspartate, branched-chain AAs; requires PLP as Schiff base intermediate), decarboxylation, racemization; heme synthesis (δ-aminolevulinate synthase: Gly + succinyl-CoA → ALA, first committed step of porphyrin synthesis → ↔ Fe, heme); neurotransmitters: GABA (glutamate decarboxylase), serotonin, dopamine; ↔ B3 & B12: PLP needed for Trp → niacin and for transsulfuration (Met → Cys via CBS/CSE); activated by riboflavin (FMN oxidase → ↔ B2)	Meat, fish, poultry, whole grains, legumes	Convulsions (↓ GABA synthesis from glutamate); microcytic hypochromic anemia (↓ heme synthesis) Peripheral neuropathy; dermatitis; impaired amino acid catabolism
Biotin (B7)	Biotin (covalently attached to Lys residue via biocytin linkage) is the CO₂-carrier for carboxylase enzymes: acetyl-CoA carboxylase (ACC: acetyl-CoA + CO₂ → malonyl-CoA, first committed step of FA synthesis → ↔ lipid synthesis); pyruvate carboxylase (pyruvate → OAA, gluconeogenesis → ↔ gluconeogenesis); propionyl-CoA carboxylase (propionate → methylmalonyl-CoA, with B12 → succinyl-CoA → ↔ B12); 3-methylcrotonyl-CoA carboxylase (Leu catabolism); ↔ hoof/skin integrity: biotin supplementation improves hoof horn quality in cattle & swine; avidin in raw egg whites binds biotin tightly → blocks intestinal absorption → biotin deficiency	Liver, cooked egg yolk, legumes; gut microbial synthesis	Dermatitis; fatty liver & kidney syndrome (FLKS, poultry); cracked hooves in swine Raw egg white → avidin-biotin complex → biotin deficiency
Folic acid (B9) → THF	Tetrahydrofolate (THF): one-carbon (C1) transfer reactions — thymidylate synthase (dUMP → dTMP, for DNA synthesis), purine synthesis, AA methylation; methionine regeneration: methyl-THF + homocysteine → Met + THF (requires B12) → ↔ B12: B12 deficiency → methyl-THF trapped ('methyl-folate trap') → functional folate deficiency even with adequate folate; ↔ B12 & B6: all three required for homocysteine metabolism; ↔ choline: both donate methyl groups for homocysteine → Met conversion (BHMT pathway uses betaine from choline)	Green leafy plants, liver, yeast, fortified grains	Megaloblastic anemia (↓ dTMP → impaired DNA synthesis → large, immature RBCs) Neural tube defects (early embryogenesis); elevated homocysteine → vascular damage
Cobalamin (B12)	Co-containing corrin ring (↔ Co: dietary Co → rumen microbes synthesize B12); two enzymatic roles: (1) methylmalonyl-CoA mutase (propionate → succinyl-CoA, TCA entry — critical for ruminant propionate gluconeogenesis; ↔ propionate/VFAs); (2) methionine synthase (homocysteine + methyl-THF → Met + THF → ↔ B9 folate: releases folate from methyl trap for thymidylate synthesis); ↔ B9: B12 deficiency → 'methyl-folate trap' → functional folate deficiency → megaloblastic anemia; intrinsic factor (gastric parietal cell glycoprotein) required for B12 absorption in terminal ileum; monogastrics need preformed B12 (animal products only)	Animal products only; rumen microbial synthesis (requires dietary Co); liver, meat, dairy	Megaloblastic anemia; neurological degeneration (subacute combined degeneration of spinal cord) Pine disease (ruminants — Co → B12 deficiency → failed propionate utilization → wasting, anemia)
Vitamin C (ascorbic acid)	Co-substrate for Fe²⁺-dependent hydroxylases: prolyl-4-hydroxylase + lysyl hydroxylase (Pro → Hyp, Lys → Hyl in collagen → ↔ Pro/Gly); keeps active-site Fe in Fe²⁺ state (ascorbate reduces Fe³⁺ → Fe²⁺) → ↔ Fe; ↔ Vit E: ascorbate (aqueous phase) reduces tocopheroxyl radical → regenerates α-tocopherol (Vit E recycling); ↔ Fe absorption: reduces dietary non-heme Fe³⁺ → Fe²⁺ in gut lumen → ↑ DMT1-mediated uptake; antioxidant (scavenges O₂•⁻, HOCl); immune function; synthesized from glucose via gulonolactone oxidase (↔ glucose) in most animals — NOT primates or guinea pigs (gulonolactone oxidase gene mutated)	Fresh fruits, vegetables; endogenous synthesis in most livestock	Scurvy (primates & guinea pigs only) — bleeding gums, poor wound healing, perifollicular hemorrhage, joint pain Not deficient in most livestock species; stress may ↓ endogenous synthesis in swine & poultry
Choline (quasi-vitamin)	Phosphatidylcholine (most abundant phospholipid — cell membranes → ↔ phospholipids; VLDL surface coat → hepatic fat export → prevents lipidosis); acetylcholine (cholinergic NMJ & CNS neurotransmitter); methyl donor via betaine: betaine + homocysteine → Met + DMG (BHMT enzyme in liver) → ↔ methionine cycle, B9, B12 (all methyl donor systems partially interchangeable); ↔ Met: SAM (from Met) can methylate phosphatidylethanolamine → phosphatidylcholine (3-step methylation — when choline intake low, Met/SAM must substitute); essential for poultry & young animals (insufficient methyltransferase capacity)	Egg yolk, soybean, liver, lecithin supplements	Fatty liver (hepatic lipidosis) — impaired VLDL assembly & export Perosis (poultry) — slipped tendon + periarticular fat; also requires Mn (glycosyltransferases) & B12
Taurine (quasi-vitamin)	Bile acid conjugation → taurocholic acid (improves emulsification of dietary fat → ↔ fat & fat-soluble vitamin absorption); retinal photoreceptor membrane stability (particularly important in cats); cardiac contractility (regulates Ca²⁺ flux in cardiomyocytes → ↔ Ca); antioxidant & osmolyte (sulfonic acid –SO₃H); synthesized from Met/Cys via cysteine sulfinic acid decarboxylase (CSAD) → ↔ Met, Cys; cats: low CSAD activity + high obligate taurine oxidation → insufficient synthesis → dietary essential; dogs may be at risk on certain grain-free diets (↓ bioavailability or altered gut microbiome affecting taurine recycling)	Meat (heart, liver), seafood; endogenous synthesis insufficient in cats	Cats: central retinal degeneration → irreversible blindness (photoreceptor outer segments degenerate) Dilated cardiomyopathy (DCM) — cats; also dogs on grain-free/legume-heavy diets Reproductive failure; small litter size, stillbirths (cats on taurine-deficient diets)
Carbohydrates(Lec 11)
Glucose (C₆H₁₂O₆)	Primary energy substrate for all tissues; absorbed via SGLT1 (Na⁺-coupled active transport → ↔ Na) + GLUT2 (basolateral exit); stored as glycogen (liver & muscle); ruminants: intestinal glucose absorption minimal — propionate (VFA) is main gluconeogenic precursor → ↔ VFAs, B12 (propionate → succinyl-CoA requires methylmalonyl-CoA mutase → ↔ Co/B12); brain, RBCs, mammary gland are obligate glucose users	Starch digestion (amylase), sucrose (sucrase), lactose (lactase), dietary glucose	Hypoglycemia → weakness, seizures; neonatal hypoglycemia in piglets Ketosis (dairy cows early lactation): glucose demand > supply → body fat mobilization → NEFA → ketone bodies (BHB, acetone, acetoacetate)
Starch (amylose + amylopectin)	Primary plant energy storage; amylose: linear α-1,4-glucose (helical); amylopectin: branched α-1,4 + α-1,6 at branch points; monogastrics: α-amylase (pancreatic & salivary) + brush-border glucosidases; ruminants: rapidly fermented in rumen → VFAs + microbial protein; ~4 kcal/g; starch source affects fermentation rate (corn > barley > wheat > oats)	Corn, wheat, barley, sorghum, rice, potatoes	SARA (subacute ruminal acidosis) — excess starch → rapid fermentation → lactic acid (lactobacilli) → pH 5.5–5.8 → acidosis Laminitis (lameness from lamellar disruption); liver abscesses (Fusobacterium); displaced abomasum
Cellulose (structural fiber)	Plant structural fiber; β-1,4-glucose linkages (indigestible by mammalian cellulases); microbial cellulases (Fibrobacter succinogenes, Ruminococcus in rumen/hindgut) ferment → VFAs; provides rumen mat (particle size ≥ 1.18 mm for effective fiber) → stimulates cud chewing → ↑ saliva → ↑ rumen pH buffer; NDF (neutral detergent fiber) measures cellulose + hemicellulose + lignin; peNDF = physically effective NDF	Forages (hay, silage, pasture), straw, alfalfa stems	SARA — insufficient effective fiber (peNDF) → ↓ cud chewing → ↓ saliva → ↓ rumen pH buffer → rumen acidosis ↓ Milk fat % (↓ acetate precursor → ↓ milk fat synthesis); displaced abomasum (DA); sub-acute laminitis
VFAs (Acetate, Propionate, Butyrate)	End-products of microbial fermentation in rumen/hindgut; absorbed across rumen wall; acetate (~65% on forage diets): primary substrate for lipogenesis (FA synthesis in adipose/mammary → ↔ milk fat) + muscle energy; propionate (~20% on grain diets): main gluconeogenic precursor in ruminants — requires B12 (propionate → methylmalonyl-CoA mutase → succinyl-CoA → TCA → OAA → glucose → ↔ Co, B12); butyrate (~15%): direct energy for rumen epithelium + stimulates rumen papillae development; ↔ Ca, Mg, Na: absorption of minerals occurs concurrently with VFA absorption in rumen	Produced by rumen/hindgut microbial fermentation of all CHO classes	SARA: ↑ lactate (lactic acid bacteria overgrowth), ↓ acetate → ↓ milk fat %, laminitis, acidosis ↓ Butyrate → stunted rumen papillae (calves) → impaired VFA & nutrient absorption capacity
Lactose (Glc + Gal, β-1,4)	Milk disaccharide; requires lactase (β-galactosidase, brush-border enzyme) for hydrolysis; major energy source for nursing neonates; galactose absorbed via SGLT1, exits via GLUT2; synthesized in mammary gland by lactose synthase (UDP-galactose + glucose → lactose; rate-limiting for milk volume — ↔ glucose requirement of mammary gland)	Milk, dairy products; not found in plants	Lactase deficiency (adult onset — normal developmental down-regulation in most mammals): undigested lactose → colonic fermentation → gas, osmotic diarrhea High lactose milk replacers can cause osmotic diarrhea in calves if gut lactase insufficient
Oligosaccharides (FOS, raffinose, stachyose)	3–10 monosaccharide units; FOS (fructo-oligosaccharides): β-fructosidic bonds → prebiotic — selectively fermented by Bifidobacterium & Lactobacillus → ↑ SCFAs + ↓ luminal pH → ↔ gut microbiome health; stachyose (Gal-Gal-Glc-Fru) & raffinose (Gal-Glc-Fru) in legumes: mammals lack α-galactosidase → undigested → colonic fermentation; soybean trypsin inhibitors & oligosaccharides both reduced by heat treatment	Legumes (soybean, beans, peas), chicory, Jerusalem artichoke	Legume oligosaccharides → colonic bacterial fermentation → flatulence, bloating Reduces apparent protein digestibility of raw soybeans; heat treatment (toasting) reduces raffinose & stachyose content
Proteins & Amino Acids(Lec 14)
Essential AAs (9 — all species)	Cannot be synthesized in adequate amounts → must be dietary; 9 EAAs: 3 BCAAs [Ile, Leu, Val — branched-chain aliphatic, catabolized primarily in muscle; ↑ demand during muscle protein synthesis]; 2 aromatic [Phe, Trp — large ring structures]; 2 basic [His (imidazole), Lys (ε-NH₂)]; 1 sulfur [Met (thioether)]; 1 polar-OH [Thr]; 4 kcal/g fuel; limiting AA concept: deficiency of 1 EAA limits ALL protein synthesis regardless of other AAs (Liebig's Law of the Minimum)	Animal protein (complete profile); soybean meal (best plant source); complementary plant proteins	↓ Growth, poor feed conversion, reduced milk/egg/wool production First limiting AA blocks all protein synthesis → deficiency pattern reflects the most deficient AA
Lysinebasic (+)	Basic AA: ε-amino group (–NH₂, pKa ~10.5) on 6-carbon aliphatic chain → positively charged at physiological pH; 1st limiting AA in corn-soybean diets (corn low in Lys); myosin & actin (muscle structural proteins); collagen crosslinking (lysyl oxidase, requires Cu → ↔ Cu); ε-NH₂ reacts with reducing sugars in Maillard/browning reaction (heat damage) → ADIN (acid detergent insoluble N) = unavailable Lys → ↓ digestibility; cannot be synthesized de novo (no α-keto acid precursor exists)	Animal protein, soybean meal; synthetic L-Lys supplement (feed-grade)	↓ Muscle accretion, poor growth rate & feed conversion efficiency Heat-damaged feeds (high ADIN) → reduced available Lys; first sign often reduced feed intake
Methioninesulfur	Sulfur AA: linear aliphatic chain with thioether (–S–, nonpolar); 1st limiting AA in dairy cows & poultry; SAM (S-adenosylmethionine) = universal methyl group donor (↔ DNA methylation, creatine synthesis, choline synthesis, carnitine, phosphatidylcholine → ↔ choline, B12, B9 all in methyl cycle); transsulfuration: Met → Hcy → Cys (CBS/CSE enzymes, PLP-dependent → ↔ B6) → taurine → ↔ Cys, taurine; rumen-protected (bypass) Met bypasses rumen degradation for dairy cows	Fishmeal, blood meal; rumen-protected Met for dairy cows; synthetic DL-Met (poultry/swine)	↓ Milk protein & yield; poor wool growth in sheep; ↓ egg quality Hepatic lipidosis (↓ phosphatidylcholine synthesis → ↓ VLDL export); impaired methylation reactions (↓ SAM)
Tryptophanaromatic	Largest essential AA (MW 204 g/mol); bicyclic indole ring (benzene fused to pyrrole, nonpolar aromatic); only AA with strong UV absorption at 280 nm (with Tyr); 2nd limiting AA in corn-soybean swine diets; niacin (B3) precursor via kynurenine pathway (requires FAD/B2 + PLP/B6 → ↔ B2, B6; 60:1 Trp:niacin ratio); serotonin precursor (tryptophan hydroxylase + BH₄ → 5-HTP → serotonin → melatonin via pineal HIOMT → ↔ pineal circadian signaling)	Soybean meal, animal protein; synthetic L-Trp supplement	↓ Growth, ↓ feed intake; impaired serotonin/melatonin synthesis Cats: black tongue-equivalent if Trp sole N source (cannot synthesize adequate niacin from Trp)
Arginine (cond. essential — cats, birds, fish)basic (+)	Most basic AA: guanidinium group (–NH–C(=NH)–NH₂, pKa ~12.5, planar + resonance-stabilized → positively charged); urea cycle (ornithine transcarbamylase pathway: NH₃ detoxification in liver → ↔ Co/B12 in propionate pathway which generates NH₃ in ruminants); NO synthesis (eNOS/iNOS: Arg + O₂ + NADPH → NO + citrulline → ↔ vascular tone, immunity); creatine synthesis (Arg + Gly → guanidinoacetate → creatine via SAM → ↔ Met/SAM, B12); essential for cats & birds: gut mucosal catabolism → insufficient citrulline for systemic Arg synthesis	Animal protein, nuts; supplemental Arg in cat food formulations	Cats/birds: hyperammonemia within hours of Arg-free meal → seizures, death (no functional urea cycle without Arg) Fish typically require dietary Arg; rapidly growing pigs may benefit from supplementation
Cysteine (cond. essential — from Met)sulfur	Polar sulfur AA: thiol group (–SH, pKa ~8.3) reversibly oxidizes → disulfide bonds (–S–S–) under oxidizing conditions → keratin (wool, hair, hoof: ~10–17% Cys), insulin (A–B chain bridge), immunoglobulins; GSH (γ-Glu–Cys–Gly) synthesis: Cys is rate-limiting for GSH → GPx substrate (↔ Se, Vit E antioxidant system); Cys → taurine via cysteine sulfinic acid pathway (CSAD enzyme → ↔ taurine quasi-vitamin); synthesized from Met via transsulfuration (CBS + CSE, both require PLP → ↔ B6, Met); becomes dietary essential whenever Met is limiting	Animal protein; synthesized from Met via transsulfuration (CBS, CSE, B6-dependent)	Poor wool/hair/hoof quality (↓ Cys–Cys crosslinks in keratin) ↓ Glutathione (GSH) → ↑ oxidative stress; becomes deficient whenever Met is limiting
Tyrosine (cond. essential — from Phe)aromatic	Aromatic AA with para-hydroxyl (phenol, pKa ~10.5); synthesized from Phe by phenylalanine hydroxylase (PAH, requires BH₄ + O₂ + NADPH); catecholamine synthesis: Tyr → L-DOPA (tyrosine hydroxylase, rate-limiting, BH₄ + Fe²⁺ → ↔ Fe) → dopamine → NE → epinephrine; thyroid hormones T₃ & T₄: TPO iodinates Tyr residues on thyroglobulin → ↔ I (iodine); melanin: tyrosinase (Cu-dependent → ↔ Cu) converts Tyr → DOPA → dopaquinone → melanin pigment; dietary essential when Phe deficient (PKU)	Animal protein; synthesized from Phe (phenylalanine hydroxylase + BH₄)	↓ Catecholamine synthesis → autonomic dysfunction; depigmentation (grey coat — ↓ melanin, Cu-dependent) PKU (phenylketonuria): blocked PAH → Tyr cannot be made → Tyr becomes essential; ↑ Phe → neurotoxic
Prolineimino	Imino acid (not amino acid): N is part of the 5-membered pyrrolidine ring → secondary amine → no free α-NH₂ → creates rigid 'kink' in peptide backbone (helix breaker & turn inducer) → essential for collagen's unique triple-helix structure; 4-hydroxyproline (Hyp) formed post-translationally by prolyl-4-hydroxylase (Fe²⁺ + O₂ + ascorbate → ↔ Vit C: keeps active-site Fe in Fe²⁺ state; ↔ Fe: enzyme requires Fe²⁺); Hyp = ~25% of collagen residues; collagen tripeptide repeat = (Gly–Pro–Hyp)ₙ; synthesized from glutamate	Synthesized from glutamate (pyrroline-5-carboxylate reductase); collagen-rich animal protein (gelatin, bone broth)	Insufficient → poor collagen quality; weak wound healing; weak connective tissue (ligaments, tendons, cartilage) Vit C deficiency → prolyl hydroxylase inactive → ↓ Hyp → unstable collagen → scurvy
Glycinenonpolar	Simplest & smallest AA (R = H, achiral — only AA without a stereocenter); every 3rd residue in collagen triple helix (Gly–Pro–Hyp)ₙ — Gly's H side chain is the only residue small enough to fit the interior of the triple helix; heme synthesis co-substrate: δ-aminolevulinate synthase (ALAS1/2: Gly + succinyl-CoA → ALA, requires PLP → ↔ B6, Fe/heme → ↔ Fe); purine ring synthesis (N-atoms from Gly); creatine synthesis (Arg + Gly → guanidinoacetate → ↔ Arg, Met/SAM); major inhibitory neurotransmitter in spinal cord/brainstem (glycine receptor, strychnine-sensitive); conditionally essential in rapidly growing animals & birds (high collagen/feather demand)	Synthesized from serine (SHMT, THF-dependent → ↔ B9 folate) or threonine; collagen-rich protein (gelatin)	Conditionally essential in fast-growing broilers (feather & collagen synthesis demand exceeds synthetic capacity) ↓ Heme synthesis if deficient (alongside B6 & Fe); ↓ purine synthesis (DNA/RNA precursor)

Exam 1

Exam 2

Exam 3

Exam 4

Exam 5

Exam 6

Exam 1Lectures 1–3 (top half) · Classes of Nutrients, Non-ruminant Digestion, Ruminant Animals

Lecture 1: Classes of Nutrients

Definitions

Nutrition: series of processes by which an organism takes in and assimilates food for growth, tissue maintenance, and production (milk, eggs, wool)
Nutrient: any chemical element or compound in the diet that supports growth, reproduction, work, lactation, or maintenance of life processes
Essential nutrient: removing it from the diet causes an abnormality; adding it back eliminates the abnormality (e.g. Ca deficiency → milk fever; Ca/P/Vitamin D deficiency → rickets)
Feed = food for farm animals; Diet = mixture of feedstuffs supplying nutrients; Ration = supply of feed at a feeding or daily

Six Main Classes of Nutrients

Water

Carbohydrates

Lipids (fats)

Proteins (amino acids)

Vitamins

Minerals

Water

Animals need ~2× as much water as dry feed intake; can survive much longer without food than without water
Makes up ~60% of body; muscle tissue ~75% water, fat tissue ~15% water
Sources: drinking water, water in food, metabolic water (from C₆H₁₂O₆ → H₂O + CO₂ + ATP)
Water loss: urine (~60%), feces, skin and lungs (15–60%)
Intake increased by: lactation (dairy cow needs ~0.9 kg water per kg milk), dietary salt, heat stress

Carbohydrates

Primary source of energy; made of repeating CH₂O units; derived from plants (except lactose)
Structural carbs: cellulose, hemicellulose (high fiber, not digestible by monogastrics without hindgut fermenters or rumen)
Non-structural carbs: sugars, starch (corn = 85% carbohydrate)

Lipids

Soluble in organic solvents; provide 2.25× more energy than carbs/proteins (9.4 kcal/g vs ~4 kcal/g)
Fats: long-chain, saturated, solid at room temp (e.g. tallow)
Oils: long-chain, unsaturated, liquid at room temp (e.g. soy oil)
Functions: energy, solvent for fat-soluble vitamins (A, D, E, K), source of essential fatty acids, palatability

Protein

Most expensive nutrient added to diets. Contains C, O, H, and N (nitrogen). Source of essential amino acids. Molecular makeup involves chains of amino acids linked by peptide bonds.

Vitamins

Fat-Soluble (A, D, E, K)

Can be stored in the animal. Fortification/enrichment needed (e.g. milk fortified with Vitamin D).

Water-Soluble (8 B vitamins + Vitamin C)

Cannot be stored — must be provided daily. B vitamins synthesized by rumen microbes in ruminants.

Fortification = adding nutrients not already present. Enrichment = replenishing nutrients lost during processing.

Minerals

Macrominerals (large amounts in body)

Calcium, Sodium, Chloride, Potassium, Magnesium, Sulfur

Microminerals / Trace Minerals

Selenium, Copper, Iron, Zinc, Cobalt

Minerals must be fed in proper balance — over or underfeeding causes serious problems. Cannot be decomposed or synthesized by the body.

Forages vs Concentrates

Component	Forage (Roughage)	Concentrate (Grain)
Energy	Low	High
Protein	Low	Low–moderate
Fiber	High (stimulates rumination)	Low
Ca & K	High	Low
Fed to	Cattle, horses, sheep, exotics	Poultry, pigs, dogs, cats, fish

Feed Efficiency

Ability of an animal to convert a unit of feed into a unit of body mass. Major determinant of cost.

Animal	Gain (kg/d)	Feed (kg/d)	Feed:Gain	Gain:Feed
Chicken	0.9	1.1	1.2	0.82
Young pig	0.3	0.5	1.7	0.60
Finishing pig	1.0	2.4	2.4	0.42
Beef steer	1.6	10	6.3	0.16

Factors affecting efficiency: diet quality, age (mature animals less efficient), composition of gain (fat vs lean), endocrine status, environment, genetics.

Lecture 2: Non-ruminant Digestion

GI Tract Types

Simple Stomach

Dogs, cats, pigs, humans. One stomach compartment.

Hindgut Fermenter

Horses, rabbits, guinea pigs, rhinoceros, elephant. Large cecum for fiber fermentation.

Avian

Chickens, turkeys. Crop → proventriculus → gizzard → short small intestine → ceca → cloaca.

Three forces acting on food in the GIT: mechanical (chewing, peristalsis), chemical (HCl, bile), enzymatic (amylase, lipase, proteases).

Stomach — Three Regions

Cardiac region: mucus secretion
Fundic region: HCl (acidifies), zymogens (pepsinogen, prorennin), mucus
Pyloric region: mucus, gastrin (hormone controlling gastric juice flow)
Zymogens are inactive enzyme precursors activated by hydrolysis (e.g. pepsinogen → pepsin)
Rennin: complex of enzymes in stomach of young pre-ruminants; curdles milk by coagulating casein into curds → retains milk longer for digestion
Lingual lipase: secreted by tongue glands; initiates fat digestion in neonates

Small Intestine

Three sections: Duodenum (digestion), Jejunum (digestion + absorption), Ileum (mostly absorption)
Villi increase surface area for absorption. Malnutrition causes villus atrophy.
Secretin (triggered by low pH) and Cholecystokinin (CCK) (triggered by lipid + peptides) secreted by duodenum

Source	Enzymes / Secretions	Substrate
Pancreas	Trypsin/Chymotrypsin/Carboxypeptidase (as zymogens), Pancreatic amylase, Pancreatic lipase + colipase	Protein, Starch, Lipid
Small intestine	Enteropeptidase (activates trypsinogen), Maltase, Sucrase, Lactase, Peptidases	Trypsinogen, Maltose, Sucrose, Lactose, Peptides
Liver/Gallbladder	Bile (bile salts)	Lipid emulsification → ↑ surface area for lipase

Absorption Mechanisms

Simple Diffusion

High → low concentration. No energy needed.

Active Transport

Against concentration gradient. Requires ATP. Important for glucose and some amino acids.

Protein-Mediated Transport

Facilitated diffusion via carrier proteins.

Hindgut Fermenters (Horses)

Large cecum (blind pouch) + large colon provide microbial fermentation of fiber
Produces short-chain VFAs (Volatile Fatty Acids), water-soluble vitamins, and protein
Only VFAs and water-soluble vitamins are absorbed from the cecum/colon
VFAs can provide over 70% of horse's energy requirement

Avian GI Tract

Crop: food storage and moistening
Proventriculus: glandular stomach (HCl + enzymes)
Gizzard: muscular stomach; mechanical breakdown using grit (sand and small stones). No sphincter separating it from duodenum.
Ceca (2): microbial fermentation, water absorption
Cloaca: common chamber for GI tract, urinary tract, and egg laying
Phytate-phosphorus (main plant P storage form) requires phytase enzyme for release

Lecture 3: Ruminant Digestion

Exam 1 — Animals, 4-Compartment Stomach, Rumen Microbes

Ruminant Animals

True ruminants (Bovidae, Cervidae, Giraffidae): cattle, sheep, goats, bison, moose, reindeer, giraffe, wildebeest, antelope. Pseudo-ruminants (Tylopoda): camels, llamas.

Key characteristic: consume large amounts of fibrous material quickly, then rest and ruminate (chew cud). Microbial fermentation in a multi-chambered foregut makes otherwise indigestible plant cellulose available — animals cannot make cellulase, but rumen microbes can.

4-Compartment Stomach

Reticulum (Honeycomb)

Origin of contractions, rumination (regurgitation), and eructation. Traps foreign objects. No enzymes secreted.

Rumen

Large fermentation vat (~100L). Papillae for absorption. pH 6–7 maintained by saliva. Contains 500,000 billion bacteria, 50 billion protozoa. Gas produced must be released via eructation — failure causes bloat (diaphragm compression → asphyxia).

Omasum

Filters digesta flow from rumen. Laminae reduce particle size. VFAs and water absorbed. No enzymes secreted.

Abomasum (True Stomach)

Only glandular compartment. Secretes HCl, pepsin, and mucus. Lysozyme in mucus breaks down bacterial cell walls. Displaced abomasum occurs when diet is too low in forage.

Rumen Microbes & Fermentation

Strictly anaerobic environment. >60 bacterial species and 20 protozoal species are normal inhabitants.
Three niches: sugar fermenters (~3% of typical diets), fiber digesters (cellulose/hemicellulose), starch fermenters (grain diets)
Protozoa: prey on bacteria, engulf starch granules, important in N recycling
Heat of fermentation: rumen is warm; up to 10% of total energy lost as heat. Asset in cold stress, liability in heat stress.
Methane: 5–10% of ingested energy lost as CH₄. Highest with forage, lowest with grain diets. Cattle in US contribute ~20% of all atmospheric CH₄.

Exam 2Lectures 3 (bottom half)–5 · VFA Production, Feed Additives, Lipids

Lecture 3 (continued): Ruminant Digestion

Exam 2 — VFA Production, Protein Digestion, Acidosis, Neonate Ruminants

VFA Production & Use

Fiber (forage) diet → high acetate

Acetate (C2): lipogenesis, energy. Propionate (C3): small proportion. Butyrate (C4): energy.

Starch (grain) diet → high propionate

Acetate (C2): reduced. Propionate (C3): 70–90% goes to liver → gluconeogenesis. Butyrate (C4): energy.

VFAs absorbed through rumen papillae → portal vein → liver. Propionate is primary gluconeogenic substrate in ruminants.

Protein Digestion in Rumen

Bacteria break down soluble protein to peptides and ammonia (enzymes on bacterial surface)
Bacteria synthesize microbial protein from the peptides and ammonia
Microbial protein digested in the abomasum (true stomach)
Excess ammonia → liver → urea → recycled in saliva or excreted in urine

Acidosis

Caused by: accidental grain overload, too-rapid diet change to high grain
Lactic acid accumulates (10× more acidic than VFAs) → rapid pH drop
Sub-acute ruminal acidosis (SARA): pH 5.0–5.5; Acute: pH ≤ 4.5
Below pH 6: cellulolytic and methanogenic bacteria decrease, amylolytic bacteria increase, Lactobacillus spp. increase
Prevention: ≥10% roughage in finishing rations, gradual diet transitions, buffers (NaHCO₃), ionophores

Neonate Ruminants

Born with non-functional rumen. Cleaned by mother. Rumen nearly functional at ~60 days. Suckling causes esophageal (reticular) groove to close → milk bypasses rumen directly to omasum. Diet drives rumen development: grain promotes papillae growth more than hay alone.

Lecture 4: Feed & Food Additives

Definitions

Non-nutritive additives: any compound added to the diet for reasons other than nutrient supply
Drugs: substances intended for treatment, prevention, or diagnosis of disease — require FDA approval
GRAS (Generally Recognized As Safe): substances with published safety/utility information; efficacy must still be proven for each new product

Non-regulated Additives

Flavors / palatants

Buffers (NaHCO₃)

Organic acids (formic, propionic, citric)

Probiotics

Prebiotics

Yeast (S. cerevisiae)

Enzymes (phytase, xylanase)

Antioxidants

Regulated Additives

Antibiotics

Ionophores (ruminants)

Anthelmintics (dewormers)

Hormones

Beta-agonists (ractopamine)

Coccidiostats (poultry/cattle)

Antibiotics

Bacteriostatic (prevent growth) or bactericidal (kill bacteria)
Used as growth promotants: control sub-clinical disease, nutrient-sparing effect, metabolic effect (more ATP available)
Problem: antibiotic resistance and potential transfer to human pathogens
FDA Guidance 209/213: strict withdrawal times before market (monitored by APHIS)
Common: Oxytetracycline, Chlortetracycline, Tylosin (Tylan), Carbadox (swine)

Ionophores (Ruminants)

Allow ions to move through cell membranes of gram-positive bacteria → selectively inhibit acetate-producing and lactic acid-producing bacteria
↑ propionate, ↓ acetate in rumen → improved feed efficiency
Also reduce bloat, acidosis, coccidiosis risk, and methane production
Used in ~95% of feedlot cattle diets (fed at 10–13 g/ton)
Monensin (Rumensin): 80% market share. ↑ feed efficiency 5–10%, ↑ weight gain 2–7%
Lasalocid (Bovatec): 15% market share
Warning: Horses DO absorb ionophores — very toxic, no treatment available

Beta-Agonists (Ractopamine)

β-adrenergic agonist — shifts energy partitioning from fat to lean muscle tissue
Not an antibiotic, not a hormone. No withdrawal period.
Paylean (pigs): last 28 days before market, 4.5–9 g/ton. ↑ carcass wt 10.6 lbs, ↑ feed efficiency 7–15%, ↑ daily gains 6–20%
Optaflexx (cattle): 200–400 mg/head/day for 28–42 days. ↑ carcass wt 15–20 lbs, ↑ feed efficiency 10–15%

Buffers, Probiotics & Enzymes

Buffers: NaHCO₃ at 0.75% DM most common for dairy cattle and feedlot cattle during diet adjustment. MgO also used. Prevent rumen acidosis on high-grain diets.
Organic acids: Citric acid most common for young pigs and chicks. Lowers stomach pH → improved protein digestion, reduced pathogen incidence.
Phytase: most common added enzyme. From Aspergillus or E. coli. Releases phytate-bound phosphorus from plant feeds; ↑ P absorption 5–7%, ↓ P excretion 50–75%. Primarily for non-ruminants.
Probiotics (direct-fed microbials): live Lactobacillus, Streptococcus, Bacillus, yeast cultures. Most effective in stressed, newly weaned, or relocated animals.
Prebiotics: non-digestible ingredients (food for good bacteria); promote lactic-acid bacteria, suppress E. coli. Primarily in pet foods.
Yeast (S. cerevisiae): source of B vitamins and mannan-oligosaccharides. In dairy cattle: higher rumen pH, ↑ cellulolytic bacteria, ↑ fiber digestion, ↑ microbial protein synthesis.

Bloat

Frothy (pasture) bloat: caused by soluble proteins and saponins from legumes (clover, alfalfa) → insufficient saliva → slime production → foam traps gas. Sudden death risk. Prevention: poloxalene (Bloat Guard) = non-ionic surfactant that consolidates gas bubbles → eructation. Mineral oil also used.

Lecture 5: Lipids

Classification of Lipids

Simple Lipids (glycerol-based)

Triacylglycerols (TAGs): 3 fatty acids ester-bonded to glycerol. >90% of dietary lipids.

Sterols: cholesterol (zoosterol), phytosterols (plants). Precursor of steroid hormones, bile acids, Vitamin D.

Compound Lipids

Phospholipids (Lecithin): major cell membrane component; amphiphilic → emulsification; body store of choline (deficiency → fatty liver).

Glycolipids: CHO + lipid; major lipids in forage leaves.

Lipoproteins: transport lipids in blood (chylomicrons, VLDL, LDL, HDL).

Non-glycerol Lipids

Waxes (surface lipids), sphingomyelins, cerebrosides, terpenes, prostaglandins.

Fatty Acids by Carbon Chain Length

Named by convention: C[length]:[double bonds], ω-[methyl-end position]. Melting point ↑ with chain length; ↓ with unsaturation (double bonds).

Formula	Name	Class	Source / Origin	Biological Role	Animal Notes
Short-Chain (C2–C6) — Volatile Fatty Acids (VFAs), water-soluble, absorbed directly into portal blood
C2:0	Acetic acid (acetate)	Sat VFA	Rumen fermentation of fiber (forage diet); vinegar	Energy (enters TCA as acetyl-CoA); substrate for lipogenesis and milk fat synthesis	60–70% of rumen VFAs on forage; ↓ on grain diets; ionophores reduce acetate production
C3:0	Propionic acid (propionate)	Sat VFA	Rumen starch fermentation (grain diet); silage	Primary gluconeogenic substrate in ruminants; enters TCA as succinyl-CoA	70–90% goes to liver on grain diet; ↑ with ionophores; critical for blood glucose maintenance in dairy cows
C4:0	Butyric acid (butyrate)	Sat VFA	Rumen fermentation; butter (3–4% of milk fat)	Energy for rumen epithelial cells and colonocytes; drives rumen papillae development	~15% of VFAs; ↑ grain diet; critical for neonatal rumen development (grain feeding initiates papillae growth)
Medium-Chain (C8–C14) — MCTs; absorbed via portal vein, bypass lymph and chylomicron packaging
C12:0	Lauric acid	Sat MCT	Coconut oil (45–55% of fat); palm kernel; some milk fat	Potent antimicrobial (gram-positive bacteria); disrupt viral lipid envelopes	Raises LDL and HDL; monolaurin antiviral; added to nursery pig diets
Long-Chain Saturated (C16–C18:0) — Solid at room temp; main storage fats in animals; absorbed via lymph as chylomicrons
C16:0	Palmitic acid	Sat	Palm oil; beef/pork tallow; de novo lipogenesis end product	Structural FA in membranes and stored fat; primary product of fatty acid synthase (FAS)	↑ LDL in excess; most abundant saturated FA in animal body
C18:0	Stearic acid	Sat	Beef tallow, cocoa butter; end product of rumen biohydrogenation	Desaturated to oleic (C18:1) by Δ9-desaturase in tissues	Uniquely does NOT raise LDL; high in ruminant fat post-biohydrogenation
Long-Chain Unsaturated (C18:1–C22:6) — Liquid at room temp; one or more double bonds
C18:1, ω-9	Oleic acid	MUFA	Olive/canola oil; lard; tallow	↓ LDL without ↓ HDL; structural membrane FA	Dominant FA in poultry and pork fat
C18:2, ω-6	Linoleic acid Essential	PUFA ω-6	Soybean, sunflower, corn oil	Skin integrity, RBC membranes, fertility; precursor to arachidonic acid (C20:4)	EFA deficiency → scaly dermatitis, poor coat; dogs/cats ≥1% DM required
C18:3, ω-3	α-Linolenic acid (ALA) Essential	PUFA ω-3	Flaxseed oil (55%), chia, green leaves	Eye and CNS structural lipid; precursor to EPA and DHA	Flaxseed feeding to hens → ω-3 enriched eggs
Very Long-Chain PUFA (C20–C22) — EFA derivatives; precursors to eicosanoids
C20:4, ω-6	Arachidonic acid (AA) Semi-essential	PUFA ω-6	Animal tissues, egg yolk	Primary eicosanoid precursor: prostaglandins, thromboxanes, leukotrienes	Cats essential: low Δ-6 desaturase → require dietary AA (≥0.02% DM)
C20:5, ω-3	EPA	PUFA ω-3	Fish oil; algae	Competes with AA for COX/LOX → less inflammatory eicosanoids; ↓ TG	Anti-inflammatory; improves fertility in mares and dairy cows
C22:6, ω-3	DHA	PUFA ω-3	Fish oil; algae; brain (40% of brain PUFA)	Neural membrane fluidity; retinal photoreceptor function; fetal brain development	Essential for neonatal brain/vision; omega-3 enriched eggs via algae meal

Eicosanoids from PUFA

From Arachidonic Acid (ω-6) — Pro-inflammatory series

PGE2, PGF2α: inflammation, fever, uterine contraction
TXA2: platelet aggregation, vasoconstriction
LTB4: neutrophil chemotaxis, bronchoconstriction

From EPA (ω-3) — Anti-inflammatory / weaker series

PGE3, PGF3α: weaker pro-inflammatory effect
TXA3: weak platelet aggregation
LTB5: weak chemotaxis

ω-3 and ω-6 compete for the same COX and LOX enzymes. Higher dietary ω-3:ω-6 ratio shifts production toward less inflammatory eicosanoids.

Lipid Digestion & Absorption

Gastric/lingual lipase begins lipid digestion in stomach (primary in neonates)
In duodenum: bile salts emulsify dietary lipids (↑ surface area)
Pancreatic lipase + colipase hydrolyze TAGs → monoacylglycerol + 2 free fatty acids
Products form micelles → absorbed across intestinal epithelium
Re-esterified into TAGs → packaged into chylomicrons → absorbed into lymph via lacteals → enter bloodstream
Lipoprotein lipase removes fatty acids from chylomicrons at capillaries → deposited in adipose or muscle

Short- and medium-chain FAs (C2–C12) bypass chylomicron packaging and are absorbed directly into the portal vein → liver.

Ruminant Lipid Considerations

Biohydrogenation: rumen microbes convert dietary unsaturated FAs → saturated FAs (adds H atoms). End product: mostly C18:0 (stearic). Produces trans FAs as intermediates.
Fatty liver disease: common in high-producing dairy cows post-partum. High free fatty acids from adipose overwhelm liver oxidation → hepatocytes fill with TAG → reduced liver function.
Ruminants have more bile acids than monogastrics, compensating for the more saturated FA profile entering the small intestine.

Exam 3Lectures 6–7 · MacroMinerals, Microminerals

Lecture 6: MacroMinerals

Overview

7 macrominerals: Ca, P, K, Na, Cl, Mg, S — needed in large amounts (>100 mg/day), measured in % of diet
Body mineral composition: Ca = 46%, P = 29%, K/Na/S/Cl/Mg = 25% combined, trace minerals <0.3%
General functions: skeletal structure (hydroxyapatite), osmotic pressure regulation, acid-base balance, enzyme activation/cofactors
Mineral excretion routes: urine (soluble minerals), feces (insoluble/unabsorbed), milk (dairy animals), sweat

CaCalciumMost abundant mineral in body (46%)

Sources

Limestone (calcite)
Dicalcium phosphate (dical)
Fish meal, meat and bone meal
Forages (alfalfa, legumes)

Functions

99% stored in bone as hydroxyapatite [3Ca₃(PO₄)₂·Ca(OH)₂]
Blood clotting (cofactor)
Muscle contraction
Nerve impulse transmission
Regulation: calcitonin (↓ blood Ca), PTH (↑ blood Ca), Vitamin D (↑ absorption)

Deficiency

Rickets: young animals; soft, malformed bones
Osteomalacia: adults; softening of bones
Osteoporosis: reduced bone density
Milk fever (dairy cows): hypocalcemia at calving — Ca secreted in colostrum → low blood Ca → muscle paralysis, recumbency, death if untreated

PPhosphorus2nd most abundant mineral (29%)

Sources

Animal products (high bioavailability)
Dicalcium phosphate (dical)
Monocalcium phosphate (monocal)
Phytate P: main plant storage form — low bioavailability in nonruminants; phytase enzyme (Aspergillus/E. coli) cleaves it → releases P

Functions

Hydroxyapatite (bone mineralization)
Acid-base balance (HPO₄²⁻ buffer)
Phospholipids (cell membranes)
DNA, RNA, ATP energy metabolism

Deficiency / Excess

Pica (depraved appetite): chewing bones, wood, etc.
Especially a concern in tropical/subtropical soils deficient in P
Excess P: eutrophication — algae overgrowth depletes dissolved O₂ in waterways (e.g., Mississippi River drainage basin)

KPotassium3rd most abundant; 98% intracellular

Sources

Grains: 0.3–0.8%
Animal products: 0.3–2.0%
Vegetable proteins: 1.0–2.5%
Plants generally high; alfalfa >2.0%
Excess K from alfalfa can be a problem for dairy cows (worsens milk fever risk)

Functions

Na⁺/K⁺ ATPase pump (3 Na out, 2 K in per cycle)
Carbonic anhydrase (acid-base, CO₂ excretion)
Salivary amylase cofactor
Osmotic balance
Nerve impulse transmission
DCAD = ([Na⁺]+[K⁺]) − ([Cl⁻]+[S²⁻]); Na,K positive; S,Cl negative
Low DCAD pre-partum → ↓ urine pH, ↑ blood Ca, ↓ milk fever incidence

Deficiency / Excess

Deficiency: extremely rare; degeneration of vital organs, nervous disorders, diarrhea
Excess K with spring grasses: impairs Mg absorption → grass tetany (weakness, tetany)
Corn silage and cereal grains are low in K

Na / ClSodium & ChlorineTable salt (NaCl)

Sodium (Na)

Sources

Plants: poor source (0.01–0.06%)
Animal products: good source (0.1–0.8%), esp. marine (fishmeal)
Supplement: salt 0.3–0.5% of diet, or free-choice salt blocks (plain, iodized, trace mineral)

Functions

Osmotic balance (primary extracellular cation)
Na⁺/K⁺ pump: drives absorption of carbohydrates and amino acids
Transmission of nerve impulses
Nutritional wisdom: Na is the main nutrient for which animals detect deficiency and seek it out

Deficiency

Causes: lactation (Na⁺/Cl⁻ secreted in milk), rapidly growing animals on cereal-based diets, tropical conditions (sweat loss)
Symptoms: pica/salt craving, licking wood/soil/sweat, loss of appetite, decreased growth, reduced milk production, weight loss
↓ osmotic pressure → dehydration → weakness; poor growth due to reduced carb/AA absorption

Chlorine (Cl)

Functions

Regulation of osmotic pressure
HCl in gastric juice → protein digestion
Pancreatic juice, bile, intestinal secretions
Required for amylase activity

Deficiency

Deficiency only on purified diets
1978: Neo-Mull-Soy/Milk-Free infant soy formulas deficient in Cl (manufacturer forgot NaCl) → 1979: recalled by CDC
Leads to metabolic alkalosis (abnormal ↑ bicarbonate)
Reduced growth, depraved appetite, emaciation

SSulfurMost reactive macromineral

Forms in the Body

Almost all S in body is in methionine + cysteine (protein-bound) and taurine (free)
Inorganic sulfates present in small quantities
Also found in: sulfides, thiamin (B1), biotin (B7)
No RDA for sulfur in humans
Glycosaminoglycans: chondroitin sulfate (cartilage, bone, tendons, blood vessel walls); heparin sulfate (plasma membrane, immune response)

Ruminant Considerations

Ruminal microbes incorporate sulfate into S-containing amino acids
S required for optimal microbial growth and thiamin & biotin synthesis
Target N:S ratio = 10:1 in ruminants
Optimum dietary S: 0.16–0.24%
Rumen bypass methionine: methionine is the most-limiting amino acid for milk protein synthesis in dairy cows

Deficiency / Toxicity

Deficiency (ruminants): reduced appetite/weight gain, anorexia, decreased wool growth (sheep), dullness, weakness, decreased milk production
Toxicity (ruminants): high S → ruminal H₂S gas (eructated & inhaled) → polioencephalomalacia (thiamin deficiency, softening of cerebrocortical grey matter); head pressing, muscle tremors, teeth grinding, rapid death

MgMagnesium60–70% in bone

Sources

Higher in forages than grains
Cool season grasses > legumes
Lower with nitrogen fertilizers (vigorous growth dilutes Mg)
Supplements: MgO (insoluble, ~50% Mg), MgCO₃, MgCl₂ (soluble), MgSO₄ (soluble)

Functions

Structural component of bone (60–70% of body Mg; bone ash 0.5–0.7% Mg)
Required for all phosphate-transferring systems (ATP → ADP)
Enzyme activation: complexed with ATP/ADP/AMP in carbohydrate and lipid metabolism; binds mRNA to ribosomes
Activator of all reactions requiring thiamin pyrophosphate (TPP) → essential for glucose metabolism
Vasodilation (reduced blood pressure)

Deficiency — Grass Tetany

Hypomagnesemia = grass tetany / grass staggers
Mainly cattle grazing cool season grasses with high K, high N, low Na → impairs Mg absorption
Also: sudden feed changes, stress, transport
Symptoms: nervousness, hyperirritability, tremors, convulsions, facial twitching, staggering gait
Treatment: i.v. Ca + Mg solution; MgO dusted on feed/pasture; Mg lick blocks; MgSO₄ or MgCl₂ in hay/silage

Lecture 7: Microminerals (Trace Minerals)

Overview

11 microminerals: Mn, Fe, Zn, Cu, Se, I, Cr, F, Co, Mo, B — needed in small amounts (<100 mg/day), measured in ppm (mg/kg)
Despite small amounts needed, deficiencies can be devastating (e.g., white muscle disease from Se deficiency)
Many function as metalloenzyme components or enzyme activators

FeIronHemoglobin 65%, Myoglobin 10%

Distribution

Functional (80%): hemoglobin 65%, myoglobin 10%, metalloenzymes 4%, transferrin (transport) 1%
Storage (20%): ferritin 15%, hemosiderin 5%

Sources

Green leafy vegetables
Legumes
Animal origin products

Deficiency

Baby pig anemia: most common — piglets born with limited Fe stores, sow's milk low in Fe → treated with iron dextran injection
Serum Fe <20 µg/dL = anemia
Signs: thumps, pale skin/mucous membranes, poor growth

CuCopperBody content: 1.5–2.0 ppm

Sources & Metabolism

CuSO₄, TBCC (tribasic Cu chloride), Cu-Lys (organic)
Bioavailability: nonruminants 5–30%, ruminants 1–80%
Transport: ceruloplasmin (90% of plasma Cu)
Homeostasis: metallothionein regulates Cu absorption

Functions

O₂-carrying proteins (ceruloplasmin)
Cytochrome C oxidase (electron transport chain)
Melanin formation (tyrosinase)
Connective tissue cross-linking (lysyl oxidase)

Deficiency / Diseases

Poor growth, anemia, depigmentation, nervous lesions
Menkes disease (humans): ATP7A gene mutation → Cu absorption defect → neurodegeneration
Wilson's disease (humans): ATP7B gene mutation → Cu accumulates in liver/brain

MoMolybdenumPurine catabolism enzyme

Functions

Xanthine oxidase: purine catabolism → hypoxanthine → xanthine → uric acid
Aldehyde oxidase: oxidizes aldehydes

Deficiency

Deficiency not reported under practical conditions
High Mo can antagonize Cu absorption (ruminants)

SeSeleniumFDA regulated: max 0.3 ppm added, 2.0 ppm tolerable

Sources

Soil-dependent (selenium distribution varies widely)
Selenomethionine (organic, plants)
Se-yeast / OH-selenomethionine
Injectable Bo-Se (selenium + Vitamin E)

Functions

Glutathione peroxidase: antioxidant enzyme protecting cells from oxidative damage
Thyroid hormone activation (5'-deiodinase)
Eicosanoid biosynthesis

Deficiency / Toxicity

Deficiency (<0.1 ppm): white muscle disease, mulberry heart disease, stiff lamb disease, suppressed immunity, impaired reproduction
Chronic toxicity: hair loss, appetite loss, damaged hooves, stiffness of joints
Acute toxicosis: staggering, labored breathing, pulmonary edema, prostration, ataxia, death; caused by overgrazing high-Se pastures or supplementation errors

FFluorineDental health; narrow therapeutic window

Sources & Body Distribution

Plants have limited ability to absorb F from soil
Forages: 2–20 ppm F; cereals: 1–3 ppm
Humans: primarily drinking water
Animals: bone meal, meat and bone meal
Body: 0.02–0.05% of apatite in bones and teeth; soft tissues rarely >2–4 ppm
F causes apatite crystals to be larger, harder, more resistant to acid
Hydroxyapatite + 2NaF → fluoroapatite (more acid-resistant) + 2NaOH

Functions (Dental)

1942: correlation discovered between F in water and ↓ dental caries prevalence
F in toothpaste/water: inhibits bacterial enolase (penultimate step of glycolysis) → disrupts bacterial acid production
Fluoroapatite resists demineralization by bacterial acids
0.7–1 ppm in drinking water reduces dental caries

Toxicity

1 ppm — reduces dental caries (beneficial)
2 ppm — mottled enamel (dental fluorosis)
8 ppm — osteosclerosis (↑ bone density, abnormal hardening)
110 ppm — reduced growth
>5 ppm — serious toxicosis in livestock
>1.5 ppm in humans — linked to birth defects, miscarriage, stillbirths
Chronic fluorosis: skin lesions, dental fluorosis, gingivitis; from F-contaminated forages near industrial plants (phosphate ore, aluminum, steel smelters)

IIodineHeaviest essential element; thyroid 70–80%

Distribution & Sources

Thyroid gland: 70–80% of body I
Muscle 10–20%, hide 4%, skeleton 3%, other organs 5–10%
Iodine is the heaviest element required by animals for physiological function
Sources: iodized salt (granular), iodized salt blocks

Functions

Component of thyroid hormones: T₃ (triiodothyronine) and T₄ (thyroxine)
I accounts for ~60% of molecular weight of T₃/T₄
Thyroid hormones regulate metabolism, growth, thermoregulation
5'-deiodinase converts T₄ → T₃ (more active form)
Regulation: I deficiency → ↓T₃/T₄ → hypothalamus releases TRH → pituitary releases TSH → thyroid enlarges

Deficiency

Goiter: enlarged thyroid gland from TSH overstimulation; 90% of human goiter cases
Animals born hairless with swollen thyroid gland
Prevalent in inland and mountain areas far from marine-derived I
Salt iodization has nearly eliminated deficiency in humans

MnManganeseMetalloenzyme activator; bone development

Functions

Enzyme activation as Mn²⁺ (metalloenzymes)
Phosphate transferases: gluconeogenesis, lipogenesis (FA synthesis)
Decarboxylases
Glycosyltransferases: synthesis of mucopolysaccharides and glycoproteins (cartilage, bone matrix)

Deficiency

May be promoted by high dietary Ca and P (compete for absorption)
Lack of Mn decreases bone phosphatase activity
Reduced growth
Perosis (slipped tendon) in young chickens: related to impaired cartilage formation
Chondrodysplasia in pregnant cattle: fetal abnormal bone development

CoCobaltVitamin B₁₂ component (cobalamin)

Functions

Constituent of vitamin B₁₂ (cobalamin)
Ruminants more sensitive to B₁₂ deficiency (B₁₂ required for gluconeogenesis from propionate)
Deficiency symptoms are those of vitamin B₁₂ deficiency, not cobalt per se

Sources

Most feedstuffs do NOT contain adequate Co levels
Estimated ruminant requirement: 0.20 ppm
Co-sulfate, Co-carbonate supplements
Soil deficiency primarily in Florida and east coast states; sandy soils also lack Cu and Fe
Co needed for optimal fiber digestion in rumen

Toxicity

Wide safety margin between toxicity and requirement
Toxicity unlikely under practical conditions due to low absorption rate
Poorly retained in body; excess Co is excreted

ZnZincSkin/hair/wool; keratinization; bone 30%

Distribution & Functions

Mainly in skin, hair, and wool (involved in keratinization)
Bone: 30% of total body Zn
Component of metalloenzymes:
Carbonic anhydrase (most Zn in RBCs)
Pancreatic carboxypeptidase A/B (protein digestion)
Lactate dehydrogenase (carbohydrate metabolism)
Zn critical for keratin formation → hoof health

Homeostasis

Controlled by rate of absorption; regulated by intestinal mucosa
Low Zn → CRIP (Cys-rich intestinal protein) enhances absorption
High Zn → metallothionein inhibits absorption (CRIP and metallothionein compete for Zn)
Factors decreasing Zn retention: dietary phytate, high Ca/Fe/Cu/Mo, excretion in pancreatic juice and feces

Deficiency

Decreased growth and appetite
Zn deficiency aggravated by high dietary Ca
Skin lesions: reddening, eruptions, scabs → parakeratosis
Reduced feathering (poultry)
Reduced immune function (abnormal thymus, T-cell dysfunction)
Majority of hoof problems in cattle related to Zn deficiency

Potentially Toxic Minerals

Classified as toxic because in biological systems, these minerals are always associated with negative effects. No known beneficial function at any concentration.

Aluminum

Arsenic

Cadmium

Lead

Exam 4Lectures 8–9 · Vitamins, Energy

Lecture 8: Vitamins

Overview

Essential organic compounds required in minute concentrations; composed of C, H, O, and sometimes N, S, Co
Not synthesized in adequate amounts by body → must be supplied in the diet
Neither energy substrates nor structural components; act primarily as enzyme catalysts (coenzymes)
Fat-soluble: A, D, E, K — stored in body (increases toxicity risk)
Water-soluble: B-vitamins and C — not stored; kidney excretes excess (lower toxicity risk)
Most discovered 1913–1941; naming convention: alphabetical order of discovery

Fat-Soluble Vitamins

Vitamin ARetinol · Vision · Epithelial integrity

Forms & Sources

Retinol (preformed, animal products), retinal, retinoic acid
Provitamins: β-carotene (plant) → 2 retinol; α/γ-carotene → 1 retinol
Richest: liver, fish liver oils, egg yolk, yellow/orange plants
Stored in liver (90%) and fat; large body reserves
1 IU = 0.3 μg retinol = 0.6 μg β-carotene

7 Functions

Visual cycle (retinal + opsin → rhodopsin)
Epithelial cell differentiation (mucosal integrity)
Bone development & remodeling
Reproduction (sperm production, fetal development)
Immune function
Growth
Antioxidant (β-carotene)

Deficiency

Night blindness → xerophthalmia (dry eye) → total blindness
Epithelial keratinization → reduced disease resistance
Skin lesions, respiratory infections
Reproductive failure, birth defects
Slow growth
Cats: spondylosis (excessive bone formation around vertebrae)

Toxicity

Hypervitaminosis A: excessive supplementation over time
Bone demineralization, joint pain, fractures
Skin lesions, anorexia, hair loss
Especially toxic for cats fed all-liver diets
β-carotene non-toxic (excess → yellow skin, not converted)

Vitamin DCalciferols · Ca/P metabolism · Most toxic fat-soluble vitamin

Forms & Metabolism

D2 (ergocalciferol): plant origin, UV irradiation of ergosterol
D3 (cholecalciferol): animal origin, UV (290–315 nm) on skin → 7-dehydrocholesterol
D2/D3 → liver (25-OH-D3) → kidney (1,25-(OH)₂D3 = calcitriol, active form)
Calcitriol is the active hormone; regulated by PTH and blood Ca/P levels
Birds prefer D3 (D2 not equivalent); ruminants prefer D2

Functions

Increases Ca/P absorption from intestine
Mobilizes Ca/P from bone (with PTH)
Promotes Ca/P reabsorption by kidney
Critical for bone/teeth mineralization
Immune function, muscle function

Deficiency & Toxicity

Rickets (young): soft/deformed bones, bent legs, beaded ribs
Osteomalacia (adult): progressive demineralization
Milk fever (hypocalcemia) in dairy cows peripartum
Most toxic fat-soluble vitamin
Hypercalcemia → soft tissue calcification (organs, blood vessels)
Calcinosis: calcification of aorta and other soft tissues

Vitamin ETocopherols · Antioxidant · Least toxic fat-soluble vitamin

Forms & Sources

α, β, γ, δ-tocopherols and tocotrienols; α-tocopherol most active
1 IU = 1 mg dl-α-tocopherol acetate
Best sources: vegetable oils, wheat germ, green leafy vegetables
Stored in adipose, muscle, liver; no single storage organ
Works synergistically with selenium

Antioxidant Function

Breaks free radical chain reactions (radical → stable product)
Protects polyunsaturated fatty acids (PUFAs) in membranes
Protects red blood cells from hemolysis
Immune function enhancement
High dietary PUFA → higher vitamin E requirement

Deficiency Syndromes

White muscle disease (cattle/sheep): nutritional myopathy, bilateral symmetrical degeneration of skeletal/cardiac muscle
Mulberry heart disease (pigs): sudden death, heart lesions resembling mulberry
Stiff lamb disease (sheep): similar to white muscle disease
Pansteatitis (cats): yellow fat disease, from high unsaturated fish diet; depression, anorexia, hyperesthesia; treat with vit E 10–25 IU 2×/day for 5–7 days
Toxicity: least toxic fat-soluble; 1,000–2,000 IU/kg no adverse effects

Vitamin KKoagulation · Blood clotting · Least body storage of fat-soluble

Forms & Sources

K1 (phylloquinone): natural, green leafy vegetables
K2 (menaquinone): natural, enteric bacteria; K2 far more bioavailable than K1
K3 (menadione): synthetic, most potent/water soluble; 1 IU = 1 μg menadione
Supplemental forms: MSB, MSBC, MNB, MPB complexes
Sources: green leafy veg, eggs, liver, fish meal; enteric bacteria synthesis
Least body storage of fat-soluble vitamins

Function: Blood Coagulation

Required for synthesis of clotting Factors: II (prothrombin), VII (proconvertin), IX (Christmas factor), X (Stuart-Prower)
Name from Danish/German "Koagulationsvitamin"
Biological assay: clotting time in young chicks
Requirement affected by: bioavailability, dietary fat, antibiotics (kill K2-synthesizing bacteria), microbial synthesis (hindgut/rumen), coprophagy

Antagonists & Toxicity

Dicoumarol: in spoiled sweet clover hay; fatal hemorrhaging in cattle ("sweet clover disease")
Warfarin: synthetic dicoumarol, used as rat poison; both prevent prothrombin synthesis by liver
Toxicity: well-tolerated; pigs tolerate 110 mg/kg; young chickens 300 mg/kg

Water-Soluble Vitamins: B-Vitamins

Not stored; kidney excretes excess. Most function as coenzymes in metabolic reactions. Generally, deficiency symptoms include poor growth, diarrhea, dermatitis, and hair loss.

Thiamin (B1)TPP coenzyme · Pyruvate → Acetyl-CoA · Beriberi

Functions & Sources

Coenzyme: thiamin pyrophosphate (TPP)
Decarboxylation of α-keto acids: pyruvate → acetyl-CoA (pyruvate dehydrogenase)
α-ketoglutarate → succinyl-CoA + CO₂ (TCA cycle)
Tryptophan → niacin/NAD conversion (60 mg Trp → 1 mg niacin); cats cannot do this → higher niacin requirement
TCA, glycolysis, gluconeogenesis, amino acid metabolism, fatty acid synthesis
Sources: yeast, pork, cereal grains (whole > refined); US flour fortified with thiamin mononitrate
Unstable to UV and Maillard reactions

Deficiency

Beriberi (humans, polished rice): dry (wasting, paralysis) or wet (capillary weakening, edema)
Polyneuritis in poultry: anorexia, cardiac enlargement, muscular weakness
↑pyruvate → ↑lactic acid → muscular weakness; ↓acetyl-CoA → ↓lipogenesis
Impaired nerve function: Na⁺-K⁺ ATPase requires ATP; thiamin deficiency → ↓ATP → nerve dysfunction
Polioencephalomalacia (polio/stargazing) in ruminants: rumen environment destroys thiamin or inhibits production via thiaminase activity

Anti-thiamin & Requirements

Anti-thiamin factors: raw fish (thiaminase); bracken fern (horses); thiaminase breaks methylene bridge → greatly increased requirement
Requirement influenced by: digestible carbohydrate intake, thiaminase intake

Riboflavin (B2)FMN & FAD · Electron transport · Curled toe paralysis

Functions

Component of flavoproteins; coenzymes FMN and FAD
Oxidation-reduction reactions; electron transport chain
Conversion of retinal → retinoic acid; tryptophan → niacin
Imparts yellow color to vitamin premixes; turns urine fluorescent yellow

Sources

Synthesized by plants, yeasts, fungi, most bacteria
Cereal grains poor; occurs in all biological materials
Good sources: yeast, liver, milk, green leafy vegetables

Deficiency

Most common dietary deficiency but rarely see symptoms
General: poor growth, diarrhea, eye abnormalities, hair loss, dermatitis
Curled toe paralysis in young chickens (peripheral nerve degeneration)

Niacin (Nicotinic Acid)NAD & NADP · Pellagra · 4 D's

Functions & Sources

Active form: nicotinamide; component of NAD and NADP
Oxidation-reduction reactions; carbohydrate, lipid, amino acid metabolism
60 mg tryptophan → 1 mg niacin (12 steps, very slow)
Cats cannot convert Trp → niacin → much higher dietary niacin requirement
Animal proteins (beef, eggs, milk) = "niacin equivalents"
Corn: low niacin/Trp AND contains niacinogen (binds niacin, reduces availability)
Cereal grains contain nyacitin (80–90% available after hydrolysis)

Deficiency

Pellagra — "disease of 4 D's": Diarrhea, Dermatitis, Dementia, Death
Necklace lesions on skin; classic in corn-based diets
"Black tongue" in dogs
Poor growth, diarrhea

High-Dose / Lipid Effects

Pharmacologic doses (1,000–2,000 mg) can reverse atherosclerosis
Reduces cholesterol, TAG, VLDL, LDL
Toxicity at 1.5–6.0 g/day: skin flushing, maculopathy, acute toxic reactions

Pantothenic AcidCoA synthesis · Fatty acid metabolism · Goose-stepping in pigs

Functions

From Greek "pantothen" = "from everywhere"; quite stable
Required for synthesis of CoA (coenzyme A)
Major role in fatty acid and carbohydrate metabolism
Addition and loss of 2-carbon units (acyl group transfer)
Synthesis and oxidation of fatty acids; TCA cycle
Component of fatty acid synthase (as acyl-carrier protein)
Required for synthesis of fatty acids, cholesterol, acetylcholine

Sources

Found in most foods/feeds (name reflects widespread occurrence)
Best sources: liver (especially chicken and pork), heart, egg yolk, yeast, molasses
Also: whole grains, wheat bran, peanuts

Deficiency

Chickens most susceptible
General: poor growth, secondary diarrhea, dermatitis, hair loss
Goose-stepping gait in pigs (spastic hindlimb movement)
Nervous system disorders

Vitamin B6 (Pyridoxine)PLP coenzyme · Amino acid metabolism · Neurotransmitters

Forms & Sources

3 forms: pyridoxine, pyridoxamine, pyridoxal
Metabolically active form: pyridoxal phosphate (PLP)
Plant: pyridoxine (stable); animal: pyridoxal/pyridoxamine (less stable)
Commercial: pyridoxine HCl (very stable)
Found in virtually all foods: yeast, liver, milk, legumes, cereal grains, vegetables

Functions

>140 pyridoxal phosphate-dependent activities
Glycogen → glucose via glycogen phosphorylase (PLP)
>½ of PLP in body stored in muscle (glycogen phosphorylase)
Macronutrient metabolism: decarboxylation, transamination, racemization; amino acid catabolism, gluconeogenesis, sphingolipid synthesis
Synthesis of neurotransmitters (serotonin, epinephrine, norepinephrine), histamine, hemoglobin

Deficiency

Poor growth rate, scaling dermatitis, hyperirritability
Muscular weakness and anemia
Infertility, fetal malformations
Insulin insufficiency (reduced pancreatic synthesis)

BiotinCarboxylase enzymes · Avidin interaction · Cracked foot pads

Functions

Found as biocytin (amide complex of biotin and lysine)
Essential component of carboxylase enzymes
Carboxylation and decarboxylation reactions (most in mitochondria)
TCA cycle/gluconeogenesis: pyruvate carboxylase, propionyl-CoA carboxylase
Lipid metabolism: acetyl-CoA carboxylase
Deamination reactions

Sources & Avidin

Few foods are good sources; wide variability in bioavailability
Good sources: egg yolk, yeast, milk, kidney, liver, soybean meal
Avidin in raw egg white: strongest non-covalent bond in nature; binds biotin (ELISA assay)
Avidin-biotin complex cannot be hydrolyzed; cooking (100°C) breaks bond
Biotin in egg yolk (not bound to avidin)

Deficiency

General: poor growth, dermatitis and hair loss
Impaired lipid and energy metabolism
Cracked pads on feet (classic sign)

Folic Acid (Folate)1-carbon metabolism · DNA synthesis · Neural tube defects

Functions

From Greek "folium" (leaf); forms: DHF (dihydrofolate), THF (tetrahydrofolate)
Carrier of methyl groups (1-carbon metabolism)
Added to/removed from amino acids (His, Ser, Met), purines, polyamines
THF: essential coenzyme for thymidylic acid synthesis (thymine → DNA)
Purine synthesis (adenine and guanine)
Initiation of translation (formylmethionine)

Sources

Green leafy materials, cereal grains, extracted oilseed meals, animal protein meals
Richest: liver (beef and chicken), brewer's yeast
Mandatory US fortification since 1996

Deficiency

Reduced DNA and RNA biosynthesis → reduced cell division
Critical for women of child-bearing age (must supplement BEFORE pregnancy)
Neural tube defects: spina bifida, anencephaly, encephalocele
Anemia (impaired erythropoiesis), leucopenia
Poor growth, reduced feed intake, dermatitis/hair loss

Vitamin B12 (Cobalamin)Microbial synthesis only · Intrinsic factor · Pernicious anemia

Sources & Absorption

Deep red color; vitamers: methylcobalamin and adenosylcobalamin
Not synthesized by plants or animals; only by microorganisms (bacteria, yeasts, algae)
Cobalt required for synthesis
Sources: meat and bone meal, fish meal, whey; all B12 from microbial origin
Intrinsic factor (IF): glycoprotein secreted by gastric parietal cells; required for active transport of IF-B12 from ileum
Only essential function of stomach; diffusion ~1% without IF
Ruminants: dietary cobalt → microbial B12 synthesis (adequate)
Non-ruminants: no cobalt requirement; synthesis not adequate (except horse via hindgut)

Functions

Synthesis of labile methyl groups; B12 coenzyme for methionine synthase
Pernicious anemia: no mature RBC; caused by lack of B12 (or lack of IF)
Glucose synthesis (critical in ruminants): propionic acid → methylmalonyl-CoA (biotin) → succinyl-CoA (B12) → glucose (gluconeogenesis)
ONLY water-soluble vitamin with significant body storage

Deficiency

Ruminants: induced by low cobalt in diet
Weight loss, wasting, listlessness; mild anemia; decreased growth and feed intake
Nervous system disorders
Limited methyl group availability → increased fat deposition in liver, heart, kidneys
Critical for vegetarian/vegan diets (no animal products)
Malabsorption in dogs: inherited disorder in Border Collies, Beagles, Giant Schnauzers; oral administration not effective

Vitamin C (Ascorbic Acid)

Vitamin CCollagen synthesis · Antioxidant · Scurvy · Poultry heat stress

Dietary Requirement

Only primates (incl. humans) and guinea pigs require dietary source
Also: certain animals from India (red-vented bulbul bird, fruit bat)
These species lack L-gulonolactone oxidase (glucose → ascorbic acid pathway)
Very soluble in water; easily destroyed by oxidation, heat, air, minerals, oxidative enzymes
Stored only to limited extent; needs regular dietary provision
Essentially non-toxic; megadoses can cause kidney stones in men

Functions

Formation of collagen (catalyst): requires hydroxyproline from proline (prolyl hydroxylase); connective tissues: bone, teeth, cartilage, tendons, ligaments, skin, blood vessels
Water-soluble antioxidant
Increases absorption of nonheme iron by reducing Fe³⁺ → Fe²⁺

Deficiency: Scurvy

Fragile capillaries and hemorrhage
Swollen, bleeding, ulcerated gums
Loose teeth, skin lesions, weak bones
Anemia (2 ways): related to activation of folic acid; reduced iron absorption

Sources & Livestock Use

Citrus fruits, bell peppers (bell pepper >> strawberry > orange)
Synthetic forms relatively inexpensive
Pharmacologic dosing does NOT reduce incidence/severity of common cold
Poultry heat stress: synthetic capacity decreases in hot temps; supplementation 200–600 mg/kg improves growth, egg production, feed efficiency, egg weight, shell quality, livability

Quasi-Vitamins

Other compounds proposed as vitamins; some (like choline) fit only for certain species.

CholinePhospholipids · Fatty liver · Critical for poultry

Background & Forms

Discovered 1864, synthesized 1866; essential nutrient for humans since 1998
Quaternary saturated amine
Fed as choline chloride (animal nutrition) or choline bitartrate (human nutrition)
Natural source: phosphatidylcholine (lecithin), enriched in soy-based ingredients

Functions & Metabolism

Component of phospholipids
Structural integrity, membrane fluidity, signaling roles in cell membranes
Methionine → choline (phosphatidylcholine) in liver
Dietary requirement influenced by methionine intake
Chickens lack this methylation enzyme → much higher dietary requirement for preformed choline

Deficiency

Rare in most species; widely distributed in foods/feeds
Typically supplemented in rapidly growing agricultural animals (pigs, especially poultry)
Young birds (chicks <13 weeks) fed low-choline diets; animals fed Met-deficient diets
Symptoms: slow growth, fatty infiltration of liver, lack of coordination, low conception rates

TaurineCat essential · Retinal degeneration · Dilated cardiomyopathy

Background

Often misnamed amino acid; technically β-amino sulfonic acid
NOT incorporated into proteins

Functions & Sources

Visual acuity, neurodevelopment, Ca regulation, antioxidant, bile acid conjugation
Seafood, meat; major constituent of bile

Cats: Taurine Requirement

Cats are unable to synthesize taurine
Deficiency leads to: Central Retinal Degeneration (CRD) → blindness
Feline dilated cardiomyopathy (heart failure)
Required in all feline foods by AAFCO

Other Quasi-Vitamins

CarnitineInositolPyrroloquinoline quinoneOrotic AcidUbiquinonep-Aminobenzoic acidLipoic acidAllyl sulfur compoundsFlavonoids and polyphenolsGlucosinolatesPhytoestrogens

Take-Home Messages

Vitamins are essential nutrients required in minute concentrations; all composed of organic elements
Fat-soluble vitamins can be stored (A, D, E, K) → increases risk of toxicity; Vitamin D is most toxic
Water-soluble vitamins cannot be stored (B-vitamins, C) → kidney excretes excess; lower toxicity risk
Most B-vitamins function as coenzymes (TPP, FMN/FAD, NAD/NADP, CoA, PLP, biotin, THF, B12-coenzyme)
Key species-specific deficiencies: Cats (taurine, niacin from Trp); Ruminants (polioencephalomalacia from thiaminase, B12 from low cobalt)

Lecture 9: Energy

Definitions & Basic Concepts

Energy = capacity to do work; measured in calories or joules
Energy is not a nutrient itself; it is derived from nutrients (carbohydrates, fats, proteins)
Ultimate currency: ATP (adenosine triphosphate)
1 calorie = heat needed to raise 1 g of water 1°C; 1 kcal = 4.185 kJ
Heat of combustion: energy released when a substance is completely oxidized (burned)

Calorimetry

Direct Calorimetry (Bomb Calorimeter)

Sample burned in O₂ atmosphere; heat measured by water temperature rise
Measures Gross Energy (GE) directly
Expensive and time-consuming; used for research

Gross Energy Values (bomb calorimeter)

Nutrient	kcal/g	kJ/g
Carbohydrates	4.1	17.2
Protein	5.7	23.9
Fats	9.4	39.3

Physiological Fuel Values (Atwater Factors)

Adjusted for digestibility and metabolic losses; used for human nutrition labeling.

4 kcal/g

Carbohydrates

Digestibility ~97%

9 kcal/g

Fat

Digestibility ~95%

4 kcal/g

Protein

Digestibility ~92%; N lost as urea

Energy Partitioning

Energy flows from gross intake through losses at each step. Each subtraction gives a more "available" form.

Gross Energy: Total energy in feed (bomb calorimeter)

− FE

Fecal Energy: Energy lost in feces (undigested feed)

Digestible Energy: GE − Fecal Energy

− UE/GasE

Urinary + Gaseous Energy: Energy lost in urine (UE) and methane/gas fermentation (GasE, especially in ruminants)

Metabolizable Energy: DE − Urinary Energy − Gaseous Energy

− HI

Heat Increment: Heat produced from digestion, absorption, metabolism (unavoidable)

Net Energy: ME − Heat Increment; energy actually available for animal use

NEm / NEp

NE for Maintenance / Production: NEm: energy for basic body maintenance; NEp: energy for growth, milk, wool, eggs

Dairy Cow Example (Mcal)

GE 78.8→DE 63.8→ME 52.3→NE 33.2

Basal Metabolic Rate & Metabolic Body Weight

Basal Metabolic Rate (BMR)

Energy expenditure at rest, fasting, thermoneutral conditions
~70% of daily energy expenditure
Organ contributions:
Liver: 27%
Brain: 19%
Skeletal muscle: 18%
Kidneys: 10%
Heart: 7%

Metabolic Body Weight (MBW)

MBW = BW⁰·⁷⁵
Accounts for surface area and metabolic scaling across species
Homeotherms: 70 kcal × MBW (kcal/day)
Poikilotherms: 18 kcal × MBW (kcal/day)
Example: 70 kg human → MBW = 70⁰·⁷⁵ ≈ 24.3 → ~1,700 kcal/day

Thermoneutral Zone (TNZ)

Temperature range within which the animal can maintain body temperature without extra energy expenditure for thermoregulation
Below TNZ (cold): extra energy needed for thermogenesis (shivering, non-shivering); less energy for production
Above TNZ (heat): evaporative cooling (panting, sweating); feed intake often drops
Optimal production occurs within the TNZ

Exam 5Lectures 10–13 · Calculations, Carbohydrates, Feed Analysis, Diet Formulation

Lectures 10, 12 & 13: Nutrient Calculations

Systems of Measurement

English System

Pound (lb), ounce (oz), ton
Foot (ft), inch (in)
Gallon, quart, pint
1 short ton = 2,000 lbs

Metric System

Kilogram (kg), gram (g), milligram (mg)
Meter (m), millimeter (mm)
Liter (L), milliliter (mL)
1 metric tonne = 1,000 kg

Universal

Percent (%) — parts per hundred
Used in both English and metric systems
Relative proportion — dimensionless

Key English ↔ Metric Conversions

English	↔	Metric
1 pound (lb)	=	454 g = 0.454 kg
2.2 lbs	=	1 kg
1 short ton (2,000 lbs)	=	907 kg
1 metric tonne (1,000 kg)	=	2,200 lbs ≈ 1.1 short tons

Relative vs. Absolute Concentration

Relative (proportional)

Percent (%) — parts per hundred
Parts per million (ppm = mg/kg)
Parts per billion (ppb = μg/kg)
Example: "12% crude protein"

Absolute (mass per mass or volume)

g/kg, mg/kg, μg/g
Example: "0.3 mg Se per kg DM"
Specifies actual mass — not dependent on total

Dry Matter (DM) Concepts

As-Is Basis

Feed as you would find it — includes water
What the animal actually consumes
Nutrient values are "diluted" by moisture
Example: fresh pasture grass (75–80% moisture)

Dry Matter (DM) Basis

Nutrient content expressed as if all moisture were removed
Standard reference for comparing feeds
100% DM is the reference — not a real feed!
Example: hay (88–92% DM)

Conversion Formulas

% DM = 100% − % Moisture

e.g. 78% moisture → 22% DM

DM basis = as-is ÷ DM fraction

e.g. 5% CP (as-is) ÷ 0.20 = 25% CP (DM)

As-is = DM basis × DM fraction

e.g. 25% CP (DM) × 0.20 = 5% CP (as-is)

DM intake = As-is intake × DM fraction

e.g. 10 kg feed × 0.90 DM = 9 kg DM

Practice: The Lassie Problem

A 2-lb can of dog food contains 78% moisture (22% DM) and 7% crude protein (CP) on an as-is basis. A dog requires 200 g CP per kg DM consumed. How many cans per day does the dog need if it consumes 2 cans?

Step 1 — Convert 2 lbs to grams:

2 lb × 454 g/lb = 908 g as-is per can

Step 2 — Find DM in one can:

908 g × 0.22 = ~200 g DM per can

Step 3 — Convert CP to DM basis:

7% CP (as-is) ÷ 0.22 = 31.8% CP on DM basis

Step 4 — CP per can (absolute):

200 g DM × 0.318 = ~63.6 g CP per can

Key insight: Always clarify whether values are on as-is or DM basis before doing calculations!

Feed and Food Analyses (Lecture 12)

Proximate analysis, Van Soest fiber system, and analytical techniques for characterizing feedstuffs

Proximate Analysis — The Weende System (1860)

Developed at the Weende Experiment Station, Germany (Henneberg & Stohmann). A sequential, gravimetric method that is cheap and fast but does not measure individual nutrients directly. Measures 6 fractions.

#	Fraction	Method	Notes
1	Moisture (Water)	Dry at 105°C for 12–16 hrs (standard); wet samples pre-dried at 57°C	% DM = 100 − % Moisture
2	Crude Protein (CP)	Kjeldahl: H₂SO₄ digestion → organic N only. Combustion: >950°C → total N. CP = %N × 6.25	6.25 factor assumes 16% N in protein; includes NPN
3	Ether Extract (EE)	Soxhlet apparatus + diethyl ether (highly explosive). Gravimetric.	Measures lipids, pigments, fat-soluble vitamins; misses some polar lipids
4	Ash	Muffle furnace at 500–600°C overnight. Organic Matter (OM) = DM − Ash.	Measures mineral content; does not identify specific minerals
5	Crude Fiber (CF)	Sequential acid + alkaline boiling (16% H₂SO₄ then 23% NaOH). Gravimetric.	Contains inconsistent portions of cellulose, hemicellulose, and lignin
6	NFE	NFE = 100 − (Moisture + CP + EE + CF + Ash)	Theoretically digestible CHO; can be negative due to compounding errors

Van Soest Detergent Fiber System

A superior system for characterizing plant fiber fractions. Better than CF but still not as accurate as Total Dietary Fiber (TDF) methods.

NDF — Neutral Detergent Fiber

= Hemicellulose + Cellulose + Lignin

Total cell wall components; negatively correlated with voluntary intake

ADF — Acid Detergent Fiber

= Cellulose + Lignin

Negatively correlated with digestibility

ADL — Acid Detergent Lignin

= Lignin only

Anti-nutrient; highly resistant to fermentation

Derived Calculations

Hemicellulose = NDF − ADF

Cellulose = ADF − ADL

NIRS — Near-Infrared Reflectance Spectroscopy

Rapid, non-destructive; no chemicals required
Must be calibrated against wet chemistry
Measures reflected light → predicts nutrient values from spectral patterns
Excellent for high-throughput labs and grain elevators

Book Values vs. Analyzed Values

Book values: averages from large datasets; quick reference
Analyzed values: from the actual feed being used; more accurate
Forages especially variable — always analyze fresh samples
For high-value rations (e.g. dairy), analyzed values are preferred

Diet Formulation (Lecture 13)

Least-cost formulation principles and hands-on methods for balancing two-ingredient diets

Information Needed Before Formulating

1. Nutrient Requirements

Change with physiological state: growth, lactation, pregnancy, maintenance. Use NRC or other species guides.

2. Feedstuff Composition

Analyzed values preferred; book values as fallback. Both nutrient profile and cost needed.

3. Cost of Feed Inputs

Drives ingredient selection; goal = meet requirements at minimum cost (least-cost formulation).

4. Species

Determines which feedstuffs are appropriate. E.g. only ruminants can utilize urea; cats require taurine.

5. Feed Processing

Affects digestibility and palatability. E.g. grinding starch, pelleting, heat treatment of proteins.

Where to Find Nutritional Data

NRC Guides

National Research Council; species-specific nutrient requirement standards

USDA FoodData Central

Comprehensive food composition database for human and animal foods

Feedipedia

Open-access FAO/INRAE database of feed ingredients worldwide

Feed Tables

Regional databases of feedstuff compositions and nutrient values

Two-Ingredient Formulation Methods

Worked example: formulate a diet with 16% CP using corn (9% CP) and protein supplement (36% CP), for a total of 100 lbs.

Algebraic Method

Let X = lbs corn, Y = lbs supplement

X + Y = 100

0.09X + 0.36Y = 16

→ Substitute X = 100 − Y:

0.09(100−Y) + 0.36Y = 16

9 + 0.27Y = 16 → Y = 25.9 lbs

X = 100 − 25.9 = 74.1 lbs corn

Pearson Square Method

Corn 9.0

→ 36−16 = 20 parts

Target: 16

Supp 36.0

→ 16−9 = 7 parts

Corn: 20/(20+7) = 74.1%

Supp: 7/(20+7) = 25.9%

⚠ Critical Caution

The target nutrient level must fall between the two ingredient values. It is mathematically impossible to formulate a 30% CP diet using ingredients with only 18% and 26% CP — the target exceeds both values.

Closed System Principle

A diet is a closed system: formulating for one nutrient (e.g. CP) inevitably changes all other nutrient concentrations. Always verify all nutrients meet requirements after balancing.

Lecture 11: Carbohydrates — Monosaccharides

General CHO overview, glycosidic linkages, classification, single-sugar units, and absorption

Introduction

General formula: [C(H₂O)]n — carbon combined with water
Make up 60–90% of dry matter in plants — the dominant energy source in most animal diets
Primary energy source for simple-stomached animals; ruminants convert structural CHO to VFAs via fermentation
Virtually absent from animal tissues (except lactose in milk, glycogen in liver/muscle)
No absolute dietary requirement — glucose can be synthesized via gluconeogenesis from amino acids and glycerol; however, the brain and red blood cells rely on glucose as their primary fuel
Energy value: 4 kcal/g (Atwater physiological fuel value); lower energy density than fat (9 kcal/g)

Glycosidic Linkages — Alpha vs. Beta

The type of bond between sugar units determines whether the carbohydrate is digestible by mammalian enzymes.

α (Alpha) Linkages — Digestible

Found in starch (amylose, amylopectin) and glycogen
α(1→4): straight chains (amylose, maltose)
α(1→6): branch points (amylopectin, glycogen, isomaltose)
Cleaved by mammalian amylase, maltase, isomaltase

β (Beta) Linkages — NOT Digestible by Mammals

Found in cellulose, hemicellulose, cellobiose
β(1→4): linear chains (cellulose, cellobiose)
Mammalian enzymes cannot cleave β linkages
Requires microbial cellulase for fermentation

Classification by Chain Length

Monosaccharides

Single sugar unit. Cannot be hydrolyzed further. Examples: glucose, fructose, galactose, ribose.

Disaccharides

Two monosaccharide units joined by a glycosidic bond. Examples: sucrose, lactose, maltose.

Oligosaccharides

3–10 units. Examples: raffinose, stachyose (legumes; flatulence). FOS = prebiotic fiber.

Polysaccharides

>10 units ('complex carbohydrates'). Examples: starch, glycogen (storage), cellulose, hemicellulose (structural).

Key Monosaccharides

Sugar	Formula	Type	Key Notes
Glucose	C₆H₁₂O₆	Aldohexose	Also called dextrose; end-product of starch digestion in monogastrics; primary fuel for brain and RBCs; absorbed via SGLT1
Fructose	C₆H₁₂O₆	Ketohexose	Sweetest natural sugar; found in fruits and honey; absorbed via GLUT5 (facilitated diffusion)
Galactose	C₆H₁₂O₆	Aldohexose (C-4 epimer of glucose)	Component of lactose (milk sugar); cannot be directly converted to glucose by poultry
Mannose	C₆H₁₂O₆	Aldohexose	Non-nutritive benefits; bacteria preferentially metabolize it; structural role in plant polysaccharides
Ribose	C₅H₁₀O₅	Aldopentose	Backbone of RNA; component of ATP, NAD; found in nucleic acids
Xylose + Arabinose	C₅H₁₀O₅	Aldopentoses	Plant cell walls; together form arabinoxylan (hemicellulose fraction in cereal grains)

Lecture 11: Carbohydrates — Disaccharides

Two-unit sugars, glycosidic bonds, brush-border enzymes, lactose, sucrose, and HFCS

Disaccharides

Two monosaccharides joined by a glycosidic bond. Brush border enzymes on the small intestinal microvilli hydrolyze them before absorption.

Disaccharide	Monomers	Bond	Enzyme	Notes
Maltose	Glu + Glu	α(1→4)	Maltase	End-product of starch digestion by amylase; "malt sugar"
Isomaltose	Glu + Glu	α(1→6)	Isomaltase	From branch points of amylopectin; produced during starch digestion
Sucrose	Glu + Fru	α(1→β2)	Sucrase	Table sugar; HIGH levels toxic to young animals (see callout)
Lactose	Glu + Gal	β(1→4)	Lactase	Milk sugar; lactase declines with age → adult intolerance (see callout)
Cellobiose	Glu + Glu	β(1→4)	Cellulase (microbial only)	Building block of cellulose; NOT digestible by mammalian enzymes

Sucrose Toxicity in Young Animals

Young animals have poorly developed sucrase activity. High sucrose intake → undigested sucrose passes to the large intestine → osmotic diarrhea and bacterial fermentation → potentially fatal dehydration. Never use sucrose in milk replacers for neonatal animals.

Lactose & Age-Related Intolerance

Lactase activity is high at birth but decreases with age in most mammals. When lactase is deficient, undigested lactose draws water into the gut (osmotic effect) and gut bacteria ferment it → diarrhea and discomfort. In suckling animals, bacteria convert lactose → lactic acid (pH 2–4), which defends against pathogens.

Lactose content in milk by species (%):

7.4%

Elephant

7.0%

Chimp

6.5%

Human

6.2%

Horse

5.8%

Sheep

5.0%

Pig

4.9%

Cat

4.8%

Cow

3.3%

Dog

0.9%

Dolphin

High-Fructose Corn Syrup (HFCS)

A mixture of glucose and fructose produced by enzymatic conversion of corn starch. Available as HFCS-42 (42% fructose) or HFCS-55 (55% fructose). Same caloric value (~4 kcal/g) and sweetness as sucrose. Widely used in processed foods.

Lecture 11: Carbohydrates — Oligosaccharides

3–10 unit chains, anti-nutritional alpha-galactosides, prebiotic FOS, and gut health

Oligosaccharides (3–10 units)

Alpha-Galactosides (Anti-Nutritional)

Raffinose (trisaccharide), Stachyose (tetrasaccharide), verbascose
Found in soybean meal: raffinose ~1.6%, stachyose ~5.6%
No mammalian alpha-galactosidase → pass undigested to large intestine
Gut bacteria ferment them → flatulence & bloating
Beano = commercial alpha-galactosidase supplement

FOS — Fructooligosaccharides (Prebiotic)

Mainly fructose units; found in artichoke, onions, garlic, green bananas
Not digestible by mammalian enzymes → classified as dietary fiber
Non-nutritive sweetener (suitable for diabetics)
Prebiotic: selectively promotes Bifidobacteria, suppresses E. coli

Prebiotic

A non-digestible food ingredient that selectively stimulates growth and/or activity of beneficial gut bacteria (e.g., FOS promotes Bifidobacteria)

Probiotic

Live microorganisms that, when administered in adequate amounts, confer a health benefit on the host (e.g., Lactobacillus in yogurt)

Lecture 11: Carbohydrates — Polysaccharides

Cell contents (starch, glycogen) and cell wall (cellulose, hemicellulose, lignin), fermentation, and processing

Polysaccharides (>10 units — "Complex Carbohydrates")

Starch — Primary Digestible CHO in Feeds

Most prominent carbohydrate in commercial animal feeds
Up to 70% in seeds, ~30% in tubers/roots; cereal grains contain 70–80% starch
Exists as compact starch granules held by hydrogen bonds — resistant to rupture until cooked

Amylose (20–30% of cereal starch)

Straight-chain polymer of D-glucose
α(1→4) linkages only — no branches
Arranged in a helix structure

Amylopectin (70–80% of cereal starch)

Branched polymer of D-glucose
α(1→4) main chain + α(1→6) branches every ~25 units
Much more branched than amylose

Starch Gelatinization & Retrogradation

Gelatinization: Cooking with water causes granules to swell → irreversible change → starch becomes soluble, binds water, forms a gel. This greatly increases digestibility. Retrogradation: When gelatinized starch is frozen then reheated, it partially re-crystallizes → forms "resistant starch" (less digestible).

Glycogen — Animal Storage Polysaccharide

Storage form of glucose in liver and muscle of animals
α(1→4) main chain + α(1→6) branches — more branching than amylopectin
Rapidly mobilized when blood glucose drops (liver glycogen → blood glucose)

Starch Digestion & Absorption

Digestion Pathway: Starch →(amylase)→ Dextrins →(amylase)→ Maltose →(maltase)→ D-Glucose

Salivary Amylase — Minor Role

Limited contact time with food in mouth
Absent in ruminants and carnivores
Only minor contribution to total starch digestion

Pancreatic Amylase — Major Role

Secreted from the exocrine pancreas in active form (unlike proteases/lipases)
Requires chloride (Cl⁻) as a cofactor; very resistant to breakdown
Pancreatic juice (pH 8.1–8.6, with bicarbonate) raises SI pH to 5–7 for optimal digestion
GI taste buds detect incoming starch → signal pancreas to secrete amylase

Small Intestinal Surface Area Amplification:

Structure	Fold Increase
Intestinal tube alone	1×
Folds of Kerckring (circular folds)	3×
Villi (finger-like projections)	30×
Microvilli / brush border	600×

Monosaccharide Absorption:

Glucose & Galactose

Via SGLT1 (Na⁺-glucose cotransporter) — active transport

Fructose

Via GLUT5 — facilitated diffusion (no energy required)

Exit to blood

All exit basolaterally via GLUT2 into portal circulation

Dietary Fiber — Non-Digestible Plant Carbohydrates

Structural polysaccharides in plant cell walls (stems, leaves, seed hulls). Cannot be digested by mammalian enzymes but can be fermented by gut microbes. Fermentation = microbial digestion.

Cellulose

Most common organic compound on Earth
Linear chain of 100s–10,000s of D-glucose units
β(1→4) linkages — cannot be cleaved by mammals
Slow fermentation due to H-bonding and tight crystalline packing
Content: cotton 90%, wood 40–50%, alfalfa 20–30%, corn silage 20%; avg ~33% of plant matter
Enzyme: cellulase (microbial only)

Hemicellulose

Shorter chains (~200 units), more complex structure than cellulose
β(1→4) linkages of mixed monomers: glucose, xylose, arabinose, galactose
~20% of most plant matter; more fermentable than cellulose
Enzyme: hemicellulase (microbial)

Arabinoxylan

Pentosans: xylose and arabinose
In cereal grains: wheat, corn, barley, especially rye
Increases viscosity of intestinal contents — problem in avian species
More fermentable than cellulose; Enzyme: xylanase / pentosanase

Pectin

In citrus fruits, apples, citrus by-products
Water-soluble; rapidly fermented by bacteria (especially in colon)
Much more fermentable than cellulose; increases intestinal viscosity
Enzyme: pectinase

Lignin — Anti-Nutrient (Not a Polysaccharide)

Made of phenylpropanoid units; not a carbohydrate but classified with cell wall components
Provides structural rigidity; interferes with breakdown of cellulose
Highly resistant to microbial degradation
Found in wood products, mature hay, straw; considered an anti-nutrient

Fiber-Degrading Enzymes (Commercially Added to Swine & Poultry Diets)

Cellulose

↓ Cellulase

Hemicellulose

↓ Hemicellulase

Arabinoxylan

↓ Xylanase

Pectins

↓ Pectinase

Fermentation & Energy from Fiber

Fermentation = breakdown of fiber by bacteria → volatile fatty acids (VFA) + gases (CO₂, CH₄)

Starch (Higher GIT — Enzymatic Digestion)

Starch → Glucose → ATP for the animal

Via host enzymes in small intestine; efficient energy capture

Fiber (Lower GIT — Microbial Fermentation)

Fiber → VFA + CO₂ + CH₄ + Heat → ATP (animal)

Energy lost to bacteria, gases, and heat — less efficient than starch

VFAs Produced: Acetate, Propionate, Butyrate

Non-ruminants: VFAs mainly from large intestine; absorbed and used by host
Ruminants: derive ~70% of energy from VFAs; >90% of fiber digested via rumen fermentation
SCFAs are a critical energy source for GIT epithelial cells (very high turnover rate: 5–6 days)

Roughage for Ruminants

Roughage is required by ruminants to maintain rumination, saliva flow, and digestive health. Without adequate roughage, rumen function is compromised.

Benefits of Dietary Fiber

GIT Health

Dietary diluent — decreases energy density
Stimulates normal peristalsis
Provides bulk → prevents constipation
Reduces GI transit time → more normal stool frequency
SCFAs from fermentation fuel colonocytes

Companion Animal Considerations

Moderately fermentable fiber is optimal for pet food
Highly fermentable fiber → rapid VFA → osmotic diarrhea, flatulence
Moderate fiber → ↑ colon weight, mucosal surface area, mucosal hypertrophy
Crude fiber in commercial pet foods: 3–6% of dry matter
Hairball control cat foods: beet pulp

Fiber Sources in Pet Food

Beet pulp

Apple/tomato pomace

Peanut hulls

Citrus pulp

Bran (oats, rice, wheat)

Cellulose (purified)

Bran = milling by-product (outer coat/pericarp of cereal grain). Pomace = solid residue after juice extraction. Pulp = fruit pulp specifically.

Carbohydrate Processing

Cooking & Extrusion

Cooking greatly enhances digestibility of starch via gelatinization
Grinding removes physical entrapment of starch granules → more accessible to amylase
Heat treatment required for maximal CHO use by companion animals
Dry pet foods: starch is essential for proper extrusion and pellet cohesion

Maillard-type Browning (Overheating)

Non-enzymatic browning caused by too much heat
Reducing monosaccharides bind irreversibly to nitrogen nutrients (especially lysine)
Makes both sugar and amino acid unavailable to the animal
Fructose more readily affected than glucose
Susceptible ingredients: alfalfa haylage and soybean meal

Carbohydrate Sources in Animal Feeds

Livestock (Swine & Poultry)

Corn, wheat, rice, oats — 70–80% starch; starch is the primary digestible CHO

Companion Animals (Dogs & Cats)

Corn, wheat, rice, oats; also barley, carrots, flax seed, molasses, peas, potatoes

Plant Carbohydrate Classification (CHO Fractions)

CHO-H (Hydrolytically Digestible)

Cell Contents — starch + sugars

Starch, disaccharides, simple sugars
Digested by host enzymes in small intestine

CHO-F_R (Rapidly Fermentable)

Cell Contents + Cell Wall — ~100% digestion

FOS, B-glucans, pectins, gums, hemicelluloses
Rapidly fermented in hindgut/rumen → VFAs

CHO-F_S (Slowly Fermentable)

Cell Wall — variable extent of digestion

Cellulose, lignin/phenolics
Slowly or poorly fermented; lignin = anti-nutrient

Energy from CHO vs. Fat in a Typical Diet:

Nutrient	kcal/g	Inclusion	Total kcal (4 kg diet)	% of Energy
CHO (Starch)	4	70%	2,800 kcal	82%
Fat	9	7%	630 kcal	18%

Fat provides more than twice the energy per gram (9 vs 4 kcal/g) but is expensive. CHO dominates as the energy source due to high inclusion rates.

Exam 6Lecture 14 · Protein & Amino Acids

Lecture 14: Protein & Amino Acids

Protein classification, non-protein nitrogen, protein structure, and amino acid essentiality

Historical Context & Importance

Term "protein" coined by Mulder (1839) from Greek proteos = "of primary importance"
Pettenkofer & Voit (1866): proteins have biological functions beyond energy supply
Voit (1872): proteins differ in nutritional value — gelatin cannot replace meat protein
Modern concept: proteins are defined by their biological value and amino acid profile

Efficiency of Protein Use in Animal Production

Species	Efficiency
Dairy cow	~26%
Beef cattle	~26%
Pig	~33%
Broiler chicken	~45%
Laying hens	~34%

Roles of Proteins in the Body

Structural

Collagen, keratin, actin/myosin

Enzymes

Catalyze all biochemical reactions

Hormones

Insulin, glucagon, growth hormone

Carriers / Transport

Hemoglobin, albumin, lipoproteins

Gene Regulators

Histones, transcription factors

Antibodies

Immune defense (immunoglobulins)

Protein Composition & Crude Protein

Elemental Composition

C: 51–55%
H: 6–7%
O: 22–24%
N: 16–18% (assumed 16%)
S: 0.5–2% (in Met, Cys, Taurine)
Also: Fe, P, Co in some proteins

Crude Protein (CP) Calculation

CP = %N × 6.25

6.25 = 100 ÷ 16 (protein ≈ 16% N)

CP includes all nitrogenous compounds — true protein AND non-protein nitrogen (NPN). Kjeldahl measures organic N; combustion measures total N.

Classification of Proteins

Simple Proteins (protein only)

Fibrous (insoluble, structural)

Collagen: most abundant protein; tendons, skin, bone
Elastin: elastic tissue (ligaments, aorta)
Keratin: hair, wool, feathers, hooves, nails

Globular (soluble, dynamic)

Albumins: water-soluble; blood albumin, egg albumin
Globulins: salt-soluble; immunoglobulins, fibrinogen
Glutelins: alkali-soluble; glutenin in wheat

Conjugated (Complex) Proteins (protein + non-protein group)

Phosphoproteins (protein + phosphate)

Casein (milk), vitellin (egg yolk)

Glycoproteins (protein + carbohydrate)

Mucus, cell surface proteins

Lipoproteins (protein + lipid)

HDL, LDL, VLDL — blood lipid transport

Chromoproteins (protein + pigment/heme)

Hemoglobin, myoglobin, cytochromes

Nucleoproteins (protein + nucleic acid)

Histones, ribosomes

Non-Protein Nitrogen (NPN)

NPN compounds contain nitrogen but are not true proteins or peptides. They are measured by Kjeldahl or combustion but cannot replace true protein amino acids. Ruminants can use some NPN (e.g., urea) for microbial protein synthesis.

Amides

Urea — major mammalian N excretion
Uric acid — avian N excretion
Allantoin

Other NPN

Free amino acids
Amines (biogenic)
Alkaloids
Nucleic acids
Ammonium salts

N Excretion by Species

Mammals (pigs): Urea (via liver/kidney)
Birds: Uric acid (solid, water-conserving)
Fish: Ammonia (directly into water)

Protein Structure

1° Primary

Sequence of amino acids in the polypeptide chain; determined by DNA

2° Secondary

Local folding: α-helix or β-sheet, stabilized by H-bonds between backbone atoms

3° Tertiary

Overall 3D shape of a single polypeptide; stabilized by disulfide bridges, H-bonds, hydrophobic interactions

4° Quaternary

Multiple polypeptide subunits assembled together (e.g., hemoglobin = 4 subunits)

Amino Acids — General Structure

Structure of α-Amino Acids

Both −COOH (carboxyl) and −NH₂ (amino) groups are attached to the α-carbon
General formula: H₂N−CH(R)−COOH where R = side chain
Side chain (R) determines identity and properties of each amino acid
Exception: Proline has an imino (−NH−) group, not a free amino group

Peptide Bond Formation

Amino acids link via condensation reactions — the carboxyl of one AA joins the amino of the next, releasing H₂O.

AA₁ + AA₂ → Dipeptide + H₂O

Polypeptides contain 10–100 AA; proteins contain >100 AA. >200 AA exist in nature; ~21 are found in proteins.

Amino Acid Classification by Essentiality

Category	Definition	Amino Acids
Essential — ALL species	Cannot be synthesized in adequate amounts; must be supplied in diet	His, Ile, Leu, Lys, Met, Phe, Thr, Trp, Val
Essential — SOME species	Required by specific species that lack synthesis pathways	Arg (cats, birds, fish) · Taurine (cats)
Conditionally Essential (from EAA)	Synthesized from an EAA; becomes essential if the precursor EAA is deficient	Cys (from Met) · Tyr (from Phe)
Semi-Essential	Normally non-essential but becomes essential during specific life stages or disease	Arg (rapid growth), Gln (disease/trauma), Pro (laying hens), Taurine (pigs)
Non-Essential	Synthesized in adequate amounts by the body from common metabolic precursors	Ala, Asn, Asp, Glu, Gly, Ser

Amino Acid 3-Letter Abbreviations

Ala

Alanine

Arg

Arginine

Asn

Asparagine

Asp

Aspartic acid

Cys

Cysteine

Glu

Glutamic acid

Gln

Glutamine

Gly

Glycine

His

Histidine

Ile

Isoleucine

Leu

Leucine

Lys

Lysine

Met

Methionine

Phe

Phenylalanine

Pro

Proline

Ser

Serine

Thr

Threonine

Trp

Tryptophan

Tyr

Tyrosine

Val

Valine