Female Reproduction

Comparative anatomy, physiology, neuroendocrine control, estrous cycles, fertilization, gestation, parturition, puberty, and seasonal reproduction (ANSC 224, Lectures 13–20)

Lecture 13Comparative Anatomy & Physiology of the Female Reproductive System

A · Animal Classification & Reproductive Strategies

Reproductive Classification

Viviparous — Live births (mammals)

Eggs fertilized inside; embryos hatch/develop inside
Placental (Eutherian) — nutrients from mother via placenta
Non-Placental (Metatherian) — marsupials (pouch as nursery)

Oviparous — Egg layers (birds, reptiles)

Eggs fertilized internally
Laid and hatch in external environment; no placenta
Exceptions: platypus, echidna (egg-laying mammals)

Mammal Reproductive Types

Eutheria — Most orders (n=21) — Placentals

Rodents, carnivores, primates, livestock

Metatheria (n=7) — Marsupials

No placenta; pouch as embryo nursery
Opossum, kangaroo

Prototheria (n=1) — Monotremes

Egg-laying mammals; platypus

Other Classification Criteria

Seasonal breeders: Induced or spontaneous; long-day or short-day breeders (e.g., sheep = short-day; regulated by melatonin / day length)

Offspring number: Monotocous (1 offspring) vs. Polytocous (litter-bearing, e.g., pig)

Uterus structure: Bicornuate, Simplex, or Duplex

Placental structure: Varies by species (diffuse, cotyledonary, zonary, discoid)

Methods to Diagnose Reproductive Status

Reproductive behaviors (observations and records)
Ultrasound
Palpation
Surgical laparoscopy
Post-mortem reproductive tract assessment
Hormone assay of milk, feces, urine, saliva, blood

B · Reproductive Tract Anatomy, Support & Blood Supply

Anatomical Parts (outside → in)

Vulva
Vestibule
Vagina
Cervix
Uterine body + horns
Oviduct (Fallopian tube)
Ovary

Also associated: Bladder, Broad Ligament, Pelvis, Rectum/Anus

Broad Ligament (Support)

Continuous with peritoneum of abdominal cavity
Contains tough connective tissue to support tract
Contains blood vessels and nerves

Anatomical parts:

Mesometrium — supports uterus
Mesosalpinx — supports oviduct (vessels for oviduct)
Mesovarium (hilus) — supports ovary

Blood Supply

Ovarian artery = direct branch off abdominal aorta; venous return matches
Aorta → common iliac → internal iliac branches:
- Uterine artery branch
- Vaginal artery branch
Blood volume increases during cycle and pregnancy
Responds to hormones (communication)
Reproductive tissues can swell: vasodilation (fluid in) + vasoconstriction (fluid retention)
Countercurrent PGF₂ transfer: uterine vein coils around ovarian artery → uterus signals ovary directly

C · Structures of the Reproductive Tract

Tubal Structure — Applies to Vagina, Cervix, Uterus, and Oviduct. Four layers from outside in:Serosa (outer single layer of flat cells) → Muscularis (inner circular + outer longitudinal smooth muscle; well developed in oviduct and uterus) → Submucosa (vessels, nerves, interstitial connective tissue; produces hormones/nutrients/fluids; changes thickness and secretions by cycle stage) → Mucosa (single layer columnar epithelial cells; oviduct = columnar + ciliated; vagina = stratified squamous)

Vulva, Vestibule & Vagina

Vulva: Labia (right and left); external opening to reproductive tract; protects sensitive mucus membranes; swells in response to estrogen (bright red swelling visible at estrus)

Perineum: Skin between vulva and anus; can tear (perineal tear) during palpation, AI, birth, constipation, or stress

Vestibule: Caudal section of vagina; from external urethral opening to labia; common passageway for urine and reproduction

Vagina: From cervix to urethral opening (bladder); functions as birth canal, urine passage, and copulatory organ; site for semen deposition in many species; Mucosa thickens at estrus to protect; immunoglobulins (IgA and IgG); low pH; secretions have odors associated with estrus

Clitoris: On ventral surface; erectile tissue

Cervix — The Neck of the Uterus

Structure: Thick-walled canal; 4 cell layers (thick); Cervical Os = opening; Mucus = major source for vagina

Lumen shape varies by species:

Smooth — dog / cat
Rings — ruminants (cow / ewe)
Interdigitating pads — sow (pig corkscrew penis twists under pressure to fit)
Folds — mare

Functions (barrier for uterus):

Limits entry of bacteria
Passageway and reservoir for sperm
Contains fetus through pregnancy
Dilates and changes shape at ESTRUS and birth
Rigid and closed during pregnancy

Uterus

Structure: 4 cell layers; uterine horns (sections separated by septum) + uterine body (common section)

Layers:

Endometrium: Mucosa (single layer luminal epithelium) + Submucosa (glands, vessels, nerves); smooth / folds / caruncles (ruminants — raised elevations for placental attachment)
Myometrium: Two muscle layers (inner circular + outer longitudinal); functions in tone and contractions; under neural and endocrine control

Functions: Sperm transport and capacitation (modify sperm); site of embryo/fetal attachment and placenta; luteal regression; birth process

Uterine Classification:

Bicornuate: Swine, cattle, sheep, horses, cats, dogs, most lab rodents — 2 horns + 1 body + 1 cervix + 1 vagina
Simplex: Humans, primates — no formed horns, 1 large body + 1 cervix + 1 vagina
Duplex: Rabbits, some rodents — 2 horns + 2 cervices (marsupials: 2 vaginas + urogenital sinus; monotremes: cloaca)

Oviduct (Fallopian Tube)

Functions: Site of fertilization; sperm reservoir; transports sperm and eggs; early embryo development

Position: Held by mesosalpinx; may form bursa enclosing the ovary

4 Sections (ovary → uterus):

Infundibulum — funnel shape; fimbriae catch ova as they are ovulated
Ampulla — site of fertilization; ~½ of duct length; highly folded columnar + ciliated epithelium
Isthmus — thick-walled; sperm reservoir
Uterotubal junction — restriction to entry; kinks in ruminants / constriction in others

D · Ovary & Follicle Development

Ovary Structure

Most species: paired ovaries, random ovulation (birds: only left side functional)

Produces: Eggs and hormones (steroids and protein hormones)

Tissue Layers:

Germinal epithelium — single outer layer
Tunica albuginea — tough connective tissue layer
Cortex — outer area; contains follicles
Medulla — connective tissue; blood vessels and nerves

Cortex develops in ovary; equivalent to medulla in testes

Follicle Development Stages

Most follicles grow microscopically below the tunica albuginea. Visible when antrum > 1 mm.

Stages:

Primordial — 1 flat layer of cells + small oocyte
Primary — 1 expanded layer + small oocyte
Secondary — 2 layers / no antrum / larger oocyte
Tertiary (Antral) / Graafian — 3+ layers + antrum; larger oocyte; depends on hormones to grow

Classified by size: Small, Medium, Large/Dominant/Ovulatory

Tiny, whitish in mice; bigger in cows

Follicle Lifecycle — Only One Remains

Surface Follicles

Growing developing layers visible as antrum expands
Small, medium, or large/dominant classification
Tertiary surface follicle size determines which one ovulates

Post-Ovulation Structures

Corpus Hemorrhagicum (CH) — immediately post-ovulation; follicle breaks surface
Corpus Luteum (CL) — progesterone-secreting; yellow body
Corpus Albicans (CA) — regressed, scarred CL

Key Concept

In monoovulatory species only one dominant follicle remains and ovulates. Follicle ovulation ruptures the surface of the ovary. All antral follicles depend on hormones (FSH/LH) to continue growing.

E · Embryonic Origin of the Female Reproductive System

Near the end of the first trimester:

1. Germ Cell Migration

Germ cells migrate toward the kidney, divide and differentiate to form the gonads

2. Mullerian Ducts (ParaM)

In females (XX): Mullerian ducts and ovaries begin to develop by default

If Y chromosome present → TDF (Testes Determining Factor) → testes form; MIF (Mullerian Inhibiting Factor) → Mullerian ducts regress

3. Degree of Duct Fusion → Uterine Type

Fusion High = Simplex (primates)
Fusion Mid = Bicornuate (livestock)
Fusion Low = Duplex (rabbits, marsupials)

Lecture 14Neuroendocrine Control of Reproduction

A · Neuroendocrine Control Overview

The Hypothalamus–Pituitary–Gonad Axis

Nervous System: Transduces internal/external signals (e.g., day length → melatonin) using neurochemical messengers

Endocrine Glands: Secrete hormones via specialized cells; travel in blood/extracellular fluids to target tissues

Endocrine — far away from target
Paracrine — adjacent to target
Autocrine — acts on self

Axis (top → down):

Hypothalamus (GnRH)
↓ via pituitary stalk
Anterior Pituitary (LH, FSH, Prolactin)
↓ Trophins
Ovary / Uterus / Placenta
↓ Steroids & Proteins (feedback)
Back to Hypothalamus & Pituitary

Female Reproductive Glands — How All Work Together

Neuroendocrine:

Hypothalamus — GnRH (releasing hormones); neurons in Surge and Tonic Centers
Pineal Gland — melatonin (day length / seasonality)

Pituitary:

Anterior — Gonadotropins (LH, FSH) + Prolactin
Posterior — Oxytocin (neuroendocrine, neural tissue)

Reproductive System:

Ovaries — Steroids and protein hormones
Uterus — Prostaglandins
Placenta — Steroids, protein hormones

Neural vs. Endocrine Responses

Endocrine (most of reproductive control)

Slower onset but lasts longer

Neural (some responses)

Fast onset and short duration
Simple reflex (standing estrus, milk letdown)

Hormone Release Patterns

Low / Basal / Tonic — baseline neuroendocrine release

Pulsatile — GnRH drives LH pulses:

High frequency, low amplitude (tonic phase)
Low frequency, high amplitude (follicular phase)

Surge / Ovulatory — massive LH surge triggered by rising estrogen; causes ovulation

P4 (progesterone) — elevated/sustained during CL phase

Blood concentration = production + release + clearance rate (determines T½)

B · Hormone Properties, Solubility & Feedback

Solubility & Transport

Peptides / Proteins — water soluble; travel freely in blood; no carrier needed

Steroids / Fatty acids — insoluble in water; require protein carriers:

Non-specific: albumin
Specific: Sex Steroid Binding Protein (SBP) or globulins

Cell Receptors: Many cells are exposed to hormones in blood, but only cells WITH receptors can bind and respond. Unbound hormone is filtered out.

Blood concentrations: ng/mL (FSH, LH, P4, insulin) to pg/mL (Estradiol 17β)

Action at Target Cell

Protein hormones → bind external (membrane) receptor → activate adenylate cyclase → cAMP → PKA cascade

Steroids → dissociate from carrier → enter cell → bind nuclear or cytoplasmic receptor → alter gene expression

Hormone-Receptor complexes internalized / degraded for clearance

Activated pathways cause:

Synthesis of hormone / enzymes
Release of stored hormones
Cell division or growth
Change in cell metabolic rate

Half-life, Clearance & Feedback

T½ (time to 50% gone): protein carriers and CHO chains increase size and extend T½

Clearance:

Small molecules cleared by kidney
Larger molecules tagged in liver with sulfate or glucuronide → pass in urine and feces

Positive feedback: Rising estrogen → LH surge (ovulatory)

Negative feedback: Progesterone → suppresses LH pulse frequency (prevents ovulation during pregnancy)

Unless a continuous source exists, steroids will be cleared

C · Peptide & Protein Hormones

Types: Peptides (~10 aa; GnRH, Oxytocin) | Proteins (larger; α and β chains; Inhibin, Relaxin) | Glycoproteins (proteins + CHO side chains = larger size and longer T½; FSH, LH)

GnRHGonadotropin Releasing Hormone

Type: Small decapeptide (10 amino acids); pGlu–His–Trp–Ser–Tyr–Gly–Leu–Arg–Pro–Gly–NH₂

Source: Hypothalamus — neurons in Surge and Tonic Centers; released from axon terminals into blood capillaries in the pituitary stalk (median eminence)

Target: Anterior pituitary gonadotrophs → binds and stimulates FSH and LH synthesis/release

Clearance: Quickly cleared (hard to measure in peripheral blood)

Synthetics: Agonists and antagonists used clinically (e.g., OvSynch reproductive protocols in cattle)

OTOxytocin — Posterior Pituitary

Type: Small peptide (9 aa)

Source: Neuron cell bodies clustered in hypothalamus (SON/PVN) produce oxytocin → travels down axon to posterior pituitary (neural tissue) → released into blood

Triggers (neural inputs):

Sexual arousal or maternal signals (sounds)
Stimulation of reproductive tract and mammary gland

Target: Smooth muscle cells in oviduct, uterus, and mammary gland → causes contraction

T½: ~minutes (short); administered exogenously as injectable

LH / FSHGonadotropins — Glycoproteins

Source: Anterior pituitary gonadotrophs — same cell can produce either FSH or LH depending on ovarian feedback and neural input (pulsatile GnRH)

Structure: Very similar to each other; common α subunit; unique β subunit gives specific receptor binding activity

FSH actions:

Follicle growth and health up to medium size
Stimulates protein and steroid production in granulosa cells

LH actions:

Follicle growth to LARGE size
Triggers ovulation + CL function (pulsatile release pattern)
Stimulates steroid pathways (androstenedione, progesterone)

Inhibin / AMHFollicular Feedback Proteins

Source: Granulosa cells of follicles

Inhibin: Protein dimer (134 AA α + 115 AA β chain); feedback to pituitary to suppress FSH; two isoforms — Inhibin A and Inhibin B

High FSH (low inhibin) in humans → indicator of menopause/low ovarian reserve

AMH (Anti-Müllerian Hormone):

Produced by granulosa cells of small follicles
High levels = many follicles and eggs available
Low levels = not many eggs left (used as ovarian reserve marker)

RelaxinPolypeptide Dimer

Structure: Small polypeptide dimer (8 kd; 24 AA α + 32 AA β chains)

Actions: Weakens and remodels connective tissues, especially the cervix — prepares birth canal for parturition

Production: Varies by species; produced near delivery; rises as progesterone falls at term

D · Steroid Hormones

Steroid overview: Derived from cholesterol (C-27); synthesized in mitochondria and ER; not water soluble → require carrier (Steroid Binding Globulin or albumin); 97% bound, only free form is biologically active; three classes: Progesterone, Androgens, Estrogens

Steroid Pathway:Cholesterol (C-27) →[StAR into mitochondria]→ P450scc → Pregnenolone →[3β-HSD-II]→ Progesterone (C-21) →[P450c17]→ 17-hydroxyprogesterone →[3β-HSD-II]→ Androstenedione (C-19) →[17β-HSD-1]→ Testosterone (C-19) →[P450arom]→ Estrone →[17β-HSD-1]→ Estradiol 17β (C-18)

ONLY cells with the specific enzymes can make each steroid. C=O groups = ketone ("-one"); C-OH = alcohol ("-ol" or "-diol")

P4Progesterone (C-21)

Source: LH stimulates follicle or CL to convert C-27 to C-21; ng/mL levels in blood

Actions:

Required for pregnancy
Uterine muscle — anti-estrogen effects (quiets contractions)
Endometrial development, secretions + hormones
Cervix closes with thick mucus
Mammary gland development
Feedback to Hypothalamus/Pituitary = decreases GnRH/LH pulse frequency

FYI: Plan B = progestogen to prevent ovulation; Abortion pill (RU-486) = P4 antagonist

C-19Androgens

Class: C-19 steroid

Source: Ovary (major); adrenal (minor)

Key androgens from follicle: Androstenedione and Testosterone

In females: Androgens are intermediates in the pathway to estrogen — not end products

Which androgen is produced depends on which enzymes the cell has

E2Estradiol 17β (C-18)

Source: Ovary — Androgen (C-19) converted to Estrogen (C-18) via P450 aromatase; Estradiol 17β most potent; in equilibrium with estrone; pg/mL levels in blood

Actions:

Positive feedback to GnRH and LH → triggers LH surge → ovulation
Secondary sex characteristics
Sexual behavior (acts on brain)
Muscle excitability (increases response to oxytocin)
Reproductive tissue growth: uterus, oviduct, cervix, vagina, vulva
Dilates arteries / constricts veins → swelling + pressure in vulva, cervix, uterus, mammary

E · Other Hormones: Prostaglandins, Pheromones & Placental

PGF₂α — Prostaglandin

Structure: Small 20-C bioactive lipid (fatty acid); cyclopentane ring + 2 straight unsaturated carbon chains with an acid at one end; synthesized from arachidonic acid by cyclooxygenase

Properties: Lipid soluble; travels bound and free; very short half-life

Produced in: Uterus (endometrium)

Actions:

Induces contractions in uterine muscles
Travels uterus → ovary via countercurrent mechanism
Constricts blood vessels to CL
Causes luteolysis (destroys CL, stops P4 production)
Used for synchronization protocols and induced parturition in some species

Luteolysis mechanism: PGF binds PGF receptor on luteal cells → activates pathways → luteal cells eventually destroyed → P4 stops

WARNING: Absorbed through skin; can cause abortion or alter cycles in women — wear gloves when handling

Pheromones

Structure: Small volatile steroids or fatty acids

Function: Reproductive communication between sexes

Chemical secreted to the outside of one animal and received by another of the same species → causes a neural reaction influencing reproductive behavior

Detection: Vomeronasal Organ (VNO) in the olfactory system (flehmen response in ungulates)

Sources:

Females: vagina, urine (e.g., Estratetraenol)
Males: sub-maxillary gland, urine (e.g., Androstadienone)

Placental Hormones

Placenta = Fetal and maternal membranes combined

Produces: Steroids and protein/glycoprotein hormones

Steroids (species-variable):

Progesterone, Estrogen, Cortisol

Glycoproteins (>> CHO chains):

eCG (equine chorionic gonadotropin) — FSH-like potency; used in superovulation protocols
hCG (human chorionic gonadotropin) — LH-like potency; basis of pregnancy tests; used in reproductive protocols

Lecture 15Estrous and Menstrual Cycles

A · When Do Females Cycle & Failure to Cycle

When Do Females Cycle?

Females cycle when they:

Reach puberty
Reach recovery in postpartum period
Are in breeding season

Why Do Animals Fail to Cycle?

Too immature
Too old
Out of season
Pregnant
Postpartum lactation
Malnourished, Diseased, Infertile

Spectrum: young | in season & not pregnant | old

The Postpartum Period

Most mammals do not cycle or express estrus during early lactation. Need time to:

Produce milk
Re-build body resources
Repair reproductive tract (Sow: ~30 d; Cow: ~60 d)

Weaning: Removes negative input from nursing on the hypothalamus (GnRH) → cycling resumes

Old Age & End of Reproductive Cycles

Animal fertility: Increases from puberty to peak at certain parities, then declines with age

End of cycles = depletion of follicles + hormones + ova

Animals: Senescence — most livestock culled before depleting ova
Women: Menopause

FYI: No estrogen/progesterone → bone and uterine health issues | Amenorrhea = absence of menses | High FSH in women = positive menopause test (due to low inhibin)

B · Classification of Estrous Cycles During the Year

Polyestrus

Cycle year-round regardless of season

Species: Pigs, cows, mice, rats

Multiple cycles per year with no seasonal pause

Diagnosed by observations or hormone assay

Seasonally Polyestrous

Cycle only during a specific breeding season; anestrus otherwise

Long-day breeders (spring/summer):

Mare (horse)

Short-day breeders (autumn/winter):

Ewe (sheep), doe (goat), cat, elk, nanny

Also wild animals; regulated by melatonin / day length

Monoestrus to Polyestrus

Limited number of cycles per year; not strictly seasonal

Domestic dog:

Non-seasonal; 1–3 estrus periods per year
Variable by breed and time of year

Wolf, fox, bear also in this category

C · Phases of the Estrous Cycle

The reproductive cycle is defined by hormones and behavior. Phases are more clearly observed in species with longer cycles. The cycle runs: Follicle Phase → Estrus (ovulation) → Luteal Phase → Follicle Phase → …

Estrous cycle length ≈ gestational length in many species

Major Phases Overview — Applicable to Most Mammals

Proestrus

Follicle phase

Estrogen Rising

Estrus

Ovulation

Peak E2 → LH Surge

Metestrus

Post-ovulation

CL Forming

Diestrus

Luteal phase

P4 Dominates

Rodents have no true luteal phase (5-day cycle; CL forms only if mated and pregnant)

Proestrus — Follicle Phase Begins

Rapid follicle growth — follicle enlarges under FSH/LH stimulation

Rising estrogen (E2) from the growing follicle

Precedes behavioral estrus; animal not yet receptive

Estrus — Peak Estrogen, Ovulation Approaching

Animal is sexually receptive — stands to be mounted (standing estrus)

Ovulation is close — triggered by LH surge from rising estrogen (positive feedback)

Characterized by large ovulatory follicle and peak estrogen

Physical changes:

Vulva and cervix: dilated, swollen, color change
Mucus production (under high estrogen)
Symptoms can be very subtle in sheep and cattle

Metestrus — Corpus Hemorrhagicum (CH) Present

Marks recent ovulation

CH: Transient structure; forms after ovulation of a large follicle; blood vessels break → bleeding and clotting

CH are hard to see on ultrasound, but indicate ovulation occurred; can see progesterone rising and large follicles of next wave

CL is forming; P4 beginning to rise

Diestrus — Luteal Phase (Progesterone Dominates)

Following ovulation, cells luteinize quickly → Corpus Luteum (CL) forms

Within days, progesterone (P4) increases significantly

P4 remains elevated for the longest part of the cycle

Ends with luteolysis (PGF₂α destroys CL) if not pregnant → new cycle

Some species (rodents, dogs/cats) do not have a true luteal phase unless mated

D · Cycle Length by Species

Cycle length: Days from one marker to the next. Marker for animals = Day 1 = estrus; Marker for menstrual cycle = Day 1 = menstruation. Livestock cycles are very consistent within a species.

Species	Cycle Length	Notes
Cow, Pig, Horse, Goat	21 days	Very consistent; major livestock species
Women / Primates	28 days	Menstrual cycle; Day 1 = menstruation
Sheep (Ewe)	17 days	Short-day seasonal breeder
Cat	16 days	Induced ovulator
Rodent	5 days	No luteal phase unless mated

E · Species-Specific Estrous Cycles

CowPolyestrus · 21-Day Cycle

Estrus duration: ~18 hours (short)

Estrus behaviors:

Mounts others, mucus discharge, vocal, active
Stands to be mounted (key diagnostic behavior)

Ovulation: 30 hours after onset of estrus

Estrus detection aids: Human observation (AM/PM), chalk marks, KAMAR patch, V or Gomer bull, pedometer

FYI Cycle stages:3d proestrus · 1d estrus · 2d metestrus · 15d diestrus

MareSeasonally Polyestrus · Long-Day Breeder

Season: Long-day breeder → estrus/ovulation mostly in spring; cycles at other times may not be normal

Cycle length: 21 days

Estrus duration: Long — 5–7 days

Heat detection: Teasing with stallion

Highly excited, posture change, raises tail, urinates, vocalizes

Ovulation: Last 2 days of estrus

FYI Cycle stages:2d proestrus · 5d estrus · 2d metestrus · 12d diestrus

Pig (Sow)Polyestrus · 21-Day Cycle

Estrus duration: ~2 days

Estrus behavior: Female stands for boar + backpressure (standing reflex)

Ovulation: Late in estrus

FYI Cycle stages:6d proestrus · 2d estrus · 2d metestrus · 11d diestrus

Sheep / GoatSeasonally Polyestrus · Short-Day Breeder

Season: Short-day breeder → autumn breeding season

Cycle length: Ewe: 17 days

Estrus: Very subtle, lasts only 1 day

Detection methods:

Teaser ram (vasectomized)
Harness marker; chin ball marker

Ovulation: After onset (~30 h) and end of estrus

RodentPolyestrus · 5-Day Cycle

Cycle length: 5 days (no true luteal phase)

Estrus duration: <1 day

Estrus behaviors:

Interest in male, hopping, darting, lordosis
FYI: Vaginal plug present if mated within 12 h

Ovulation: 12 h after onset of estrus

Unique: Forms CL only if mated and pregnant after day 5 — no CL otherwise (no internum unless mated)

FYI: E2 and P4 both increase from follicle at estrus (not from CL)

DogMono/Polyestrus · Non-Seasonal

Pattern: 1–3 estrus periods per year; variable by breed; non-seasonal

Proestrus (~9 days):

Follicle development
Blood discharge from uterus (spotting — uterine bleeding, NOT menses)
Estrogen → vulva swelling

Estrus (~9 days):

1st day accepts male; ovulates on day 2–3 of estrus

Diestrus:

Starts day 1 of refusal; CH forms
CL lifespan is fixed regardless of breeding → pseudopregnant

Lecture 16The Follicle Phase and Ovulation

A · Follicle Development & Types

Ovulation Type by Species

Monotocous — ovulate ONE dominant follicle per cycle (cow, mare, ewe, woman)

Polytocous — ovulate MULTIPLE large follicles per cycle (sow, bitch, queen, rat)

Follicles on Ovaries During a Cycle

Numerous 1°, 2°, 3° follicles always growing regardless of cycle phase

Large/dominant follicles only in late follicle phase for spontaneous and induced ovulators

Ruminants (cattle) — have large/dominant follicles in BOTH luteal and follicle phases (wave-type development)

Superovulation & Litter Size

Superovulation (exogenous FSH/LH) → more follicles recruited → more ovulations → more embryos for transfer

Ovulation rate is the #1 limiting factor for litter size in polytocous species

Increasing ovulation rate increases litter size up to uterine capacity limit

The Follicle Phase (Proestrus)

Early proestrus — NO species have dominant/ovulatory follicles yet

Late proestrus — ALL species have dominant/ovulatory follicle(s)

FYI: What allows follicle phase to start? Puberty, being in season (photoperiod), post-partum recovery, or luteolysis

B · Follicle Lifespan: Recruitment → Selection → Dominance

Recruitment

Primordial follicles leave resting pool → join growing pool

Antral follicles become sensitive to FSH

Occurs continuously throughout reproductive life

Selection

Medium follicles grow to large size

Estrogen active (high E2 production)

Produce inhibin → reduces FSH → suppresses competing follicles (atresia)

Dominance & Atresia

Selected follicle(s) become dominant

Others undergo atresia (apoptosis)

Dominant follicle switches to LH dependence for final growth

Follicle Size & Hormone Receptors

SmallMediumLarge

FSH-R onlyFSH-R + LH-RLH-R only

As follicles grow, they transition from FSH-dependence → FSH+LH → LH-dependence for final maturation

FYI: Follicles in Women (Atresia)

6 million — fetus (peak)

400,000 — newborn

40,000 — puberty

~35,000 — age 20 | ~25,000 — age 37 | ~1,000 — age 50

Most undergo ATRESIA — ~588 lost per year (ages 20–37)

Only ~400 total ovulated in a lifetime

C · Follicle Anatomy & 2-Cell Steroid Production

Parts of an Antral Follicle

Theca Externa — outer connective tissue layer

Theca Interna — inner theca; has LH receptors; converts C27 cholesterol → C19 androgens

Basal Lamina — separates theca from granulosa

Granulosa — has FSH receptors; converts C19 androgens → C18 estradiol (E2)

Antrum — fluid-filled cavity containing hormones, proteins, steroids, and the egg/cumulus complex

2-Cell, 2-Gonadotropin Theory

Theca Interna (LH)

C27 (Cholesterol) → C19 (Androgens: androstenedione, testosterone)

↓ (crosses basal lamina)

Granulosa (FSH)

C19 (Androgens) → C18 (Estradiol / E2) via aromatase

Both cell types + both gonadotropins (LH & FSH) required for E2 production

FYI — Comparative Ovulatory Follicle Size:

Rat: 0.7 mmQueen: 2 mmBitch: 7 mmEwe: 10 mmSow: 12 mmWoman: 18 mmCow: 18 mmMare: 50 mm

D · Follicle Phase Sequence: Proestrus → Estrus → Ovulation

Sequence of Events

1.Follicle(s) selected and grow to large size

2.Other follicles regress (atresia)

3.Rising estrogen (E2) → positive feedback

4.GnRH pulse frequency increases

5.LH pulse frequency & amplitude increase

6.E2 reaches threshold → ESTRUS behavior

7.LH surge (preovulatory)

8.OVULATION!

Hormone Pattern During Follicle Phase

GnRH — pulse frequency increases in late proestrus

FSH — drives early follicle growth; declines as inhibin rises

LH — pulses increase; massive surge triggers ovulation

Progesterone (P4) — low during follicle phase (no CL)

Estradiol (E2) — rises steeply; triggers LH surge

Inhibin — rises with follicle growth; suppresses FSH

E · Species-Specific Follicle Phases

Pig (Sow)

Selects ovulatory follicles over 4–5 days

Follicle recruitment funnel:

~40 small follicles recruited

→ ~25 medium selected

→ ~18 large (ovulatory)

Polytocous — all 18 ovulate in a litter

Horse (Mare)

Proestrus over 6 days

Develops ONE single dominant large follicle (~50 mm)

Maintains 5–7 days of estrus (longest of domestic species)

Monotocous — one ovulation per cycle

Cattle (Ruminants) — Wave Type

~3 follicle waves per 21-day cycle

Each wave: Recruitment → Selection → Dominant → Atresia

Only the wave coinciding with luteolysis produces an ovulatory follicle

Dominant follicles present even during luteal phase (suppressed by P4)

FYI — Primates (Women): Follicle Timeline per Cycle

Day −15 — Recruitment: 3–30 follicles enter growing pool

Day −9 — Cohort selected (several medium follicles)

Day −5 — Dominance established (one follicle takes over)

Day 0 — Ovulation (LH surge → egg released)

Counting backwards from ovulation (Day 0 = ovulation ~Day 14 of a 28-day cycle)

Lecture 17The Luteal Phase, Metestrus and Diestrus

A · Ovulation Mechanics

Ovulation Mechanism

After the LH surge, enzymes are activated (stimulated by P4) to break down collagen in the follicle wall (tunica)

Blood vessel dilation increases intrafollicular fluid pressure

Follicle wall weakens → rupture

Egg, cumulus cell complex, and follicular fluid are expelled from the ovary

Key Points

Ovulation is NOT an explosion — a slow, controlled rupture

Progesterone (P4) plays an early role in activating proteolytic enzymes even before the CL fully forms

Collagenase and other enzymes digest the extracellular matrix at the follicle apex (stigma)

Infundibulum of the oviduct captures the egg/cumulus mass

B · Corpus Hemorrhagicum (CH) & Corpus Luteum (CL) Formation

Corpus Hemorrhagicum (CH)

Ovulation ruptures blood vessels lining the follicle wall

Blood fills the collapsed follicle cavity and clots → Corpus Hemorrhagicum

Visible as a red/brown structure on the ovary immediately after ovulation

Transient structure — precursor to the CL

Corpus Luteum (CL) Formation

LH induces luteinization of theca and granulosa cells → they become luteal cells

CL forms by cell hyperplasia (cell number ↑) and hypertrophy (cell size ↑)

CL = yellow, vascularized gland; primary source of progesterone (P4) during luteal phase

FYI: Pig CH and CL timeline: Day 0 (ovulation) → Day +5 CH → Day +16 functional CL

C · Progesterone Production & Luteal Phase Profile

Luteal Cell P4 Production

LH dependent — LH receptors drive steroidogenesis

Designed for HIGH P4 output (ng/mL range, vs pg/mL for E2)

Solid cell mass (not hollow like follicle) — maximizes steroidogenic capacity

Simplified steroid pathway: Cholesterol → Pregnenolone → Progesterone (limited enzyme steps)

FYI: CL of primates (humans/great apes) can ALSO produce estrogen (pg levels) in addition to P4

Luteal Phase P4 Profile (Cow, Day 1–21)

Days 1–5 — CL forming; P4 rising slowly

Days 5–16 — CL fully formed; P4 high and sustained (ng/mL)

Days 17–21 — CL regressing (luteolysis); P4 drops rapidly → next cycle begins

Pattern applies broadly to cow, ewe, sow — luteal phase lasts ~14–16 days in most domestic species

D · Progesterone Effects & Ovary Feedback

Ovary Feedback — P4 & GnRH/LH

P4 → negative feedback on hypothalamus/pituitary

↓ GnRH pulse frequency → ↓ LH pulse amplitude and concentration

Inhibits the LH surge center → prevents estrus and ovulation during luteal phase

Prevents estrus behavior (animals won't stand for breeding)

Applications:

• Progestins (synthetic P4) used to synchronize / suppress estrus in cattle management

• Detect P4 fall to predict onset of next estrus

Progesterone Effects on Reproductive Tract

Uterus:

Endometrial gland growth and secretions (histotroph/"uterine milk")
Uterus thickens (degree varies by species)
Inhibits myometrial contractions (↓ E2 receptors & OT receptors)

Cervix:

Mucus thickens → forms a plug
Prevents dilation (closes reproductive tract)

Luteal Phase in Women

Secretory phase — high P4 from CL; endometrium thickens, glands grow and secrete; prepares for implantation

Menstrual phase — luteolysis ends P4 support; endometrium lost/shed (menstruation)

Menstruation = loss of endometrium at end of luteal phase when CL regresses without pregnancy

Myometrium Contraction Control

Induces contraction:

Estradiol — upregulates oxytocin receptors (OXY-R)
Oxytocin — binds OXY-R → contraction
Prostaglandin — binds PG receptors → contraction

Inhibits contraction:

Progesterone — reduces OXY-R and E2 receptors

E · Luteolysis — Corpus Luteum Regression

Mechanism of Luteolysis

PGF₂α (Prostaglandin F2 alpha) is the primary luteolytic hormone

PGF₂α binds CL receptors → triggers luteal cell apoptosis (programmed death)

CL regresses → P4 drops → negative feedback removed → next follicle phase begins

Result: Corpus Albicans (CA) — white scar tissue remaining after CL regression

Exogenous PGF₂α injection can be used clinically to lyse CL and synchronize estrus

Source of PGF₂α by Species

Uterus is the source (utero-ovarian countercurrent exchange):

Mare (horse)
Sow (pig)
Cow (cattle)
Ewe (sheep)

Uterus is NOT the source:

Women (humans)
Dogs
Cats

CL still sensitive to exogenous PGF₂α in these species

Lecture 18Fertilization and Early Gestation

A · The Mammalian Egg

Mammalian vs. Chick Egg

Mammalian egg:

Largest cell in the body
Limited yolk — nourished inside the mother

Chick egg:

Single cell, but mostly yolk (vitellus)
Contains all nutrients to support development outside the mother

Primary Oocyte

What most mammals are born with

The developing egg (oocyte) matures in a recruited follicle

Oocyte has a nucleus and a large cytoplasm

FYI: nucleus also called germinal vesicle

In primordial and primary follicles: surrounded by a single flat layer of follicle cells

Zona Pellucida

The mammalian egg has a zona pellucida (ZP)

Structure: Thick glycoprotein coat around the egg membrane

Functions:

Protects the egg
Sperm selection (species-specific receptor binding)
Prevents polyspermy (ZP reaction after 1st sperm entry)

FYI: Chick eggs have only a vitelline membrane (no zona pellucida)

B · Oocyte Maturation & Fertilization

Final Oocyte Maturation

Occurs after the LH surge

After the LH surge:

Granulosa cell changes (luteinization begins)
Meiosis resumes in the egg (was arrested at prophase I)
1st polar body expelled
Secondary oocyte formed (arrests at metaphase II)
Ovulation occurs

Fertilization

Steps:

Sperm penetrate cumulus/corona cells surrounding the egg
Sperm binds and penetrates zona pellucida (ZP reaction blocks polyspermy)
Sperm penetrates vitelline membrane
2nd polar body expelled → egg completes meiosis II

Fertilization occurs in the ampulla of the oviduct

Zygote Formation

Zygote: New organism forms when pronuclei fuse (1 diploid cell)

Sperm pronucleus + egg pronucleus → single nucleus with full diploid chromosome set

Sex determined at fertilization by X or Y chromosome from sperm

Timing of Fertilization

Mammalian species ovulate during estrus and the LH surge; eggs move into oviduct

Depends on timing of insemination:

Egg lifespan may only be hours (species-dependent)
AI too early or too late reduces fertilization rate

Long estrus allows multiple matings to ensure sperm are present at ovulation

C · Breeding, Sperm Transport & Timing

Natural Service vs. Artificial Insemination (AI)

Natural service/mating:

Ejaculation volume larger; much more sperm
Some species have a gelatin plug (stallion, boar, dog, rodent)

Natural service deposition site:

Vagina — cattle, sheep, primates, rodents, horses
Cervix — pigs (corkscrew penis)
FYI: Cloaca — chicken (everted cloaca, small volume)

AI deposition site:

Cervix→uterus — pig
Uterus (deep) — cattle, sheep, humans
FYI: Laparoscopic AI into oviduct — sheep

Sperm Transport & Reservoir

Sperm transported to oviduct and binds in isthmus/ampulla to establish a sperm reservoir

Sperm membrane is capacitated in the female reproductive tract (membrane changes enable fertilization)

Ovulated eggs transported to ampulla (site of fertilization)

Transport must allow for: establishment of reservoir + capacitation of sperm

Sperm Survival (Natural Service)

Duration of sperm fertility not always clear; estimates:

Women: up to 5 days (avg ~1.4 d sperm / 0.7 d for egg)
Dogs: 9–11 days
Mares: 4–5 days
Pigs: 2 days
Cattle: 1–2 days
Birds: weeks to a month (sperm storage tubules)

Optimizing Breeding Timing

Chances of conception improved by insemination close to but ahead of ovulation (sperm must be capacitated and waiting)

In litter-bearing species, multiple sires mating around ovulation can contribute to a single litter (superfecundation)

Includes induced ovulators (e.g., cat, rabbit, camel) — coitus induces LH surge → ovulation; help induce by stimulation

D · Early Embryo Development

Gestational Stages (Trimesters)

Gestation divided into 3 unequal trimesters:

1st Trimester — Embryo Stage:

Early stages — no identifiable limbs or species-specific form
Organs forming (organogenesis)

2nd Trimester — Fetal Stage:

Recognizable species form
Limbs and organs differentiated

3rd Trimester — Growth Stage:

Rapid growth and organ maturation

Cleavage Stage Embryo

Zona pellucida maintained — allows normal development; remains intact during early cleavage

Cells = blastomeres — divide mitotically (2-4-8-16 cells)

Embryo increases in cell number but reduces in cell size (total volume stays constant within ZP)

Timing (approximate; species-variable):

2-cell: 18 h post-fertilization
4-cell: 32 h · 8-cell: 54 h
Morula: 4 days
Blastocyst: 7 days · Hatching: ~8 days

May enter uterus at 48–72 h (still cleaving)

Blastocyst Stage — Cell Fate Specification

Inner Cell Mass (ICM)

From cells with gap junctions (inner cells)
→ Internal organs, glands, skeleton, muscle
Embryoblast — forms the embryo proper

Trophectoderm (Trophoblast)

From outer cells with tight junctions
→ Placental membranes
→ Neural tissue, sense organs, skin

Blastocoele Cavity

Fluid-filled cavity forms inside blastocyst
Expands, pushing ICM to one side
Zona pellucida hatches at ~day 8 → embryo can attach to uterus

Lecture 19Gestation, Parturition and Postpartum Recovery

A · Placental Classification

The placenta is classified by the distribution of villi (chorion folds/projections) on the surface of the chorion.

Diffuse Placenta

Species: Pig, Horse (mare)

Feature: Numerous villi distributed over entire chorion surface

At day 35: Horse chorion forms as extended oval/localized; pig conceptuses cover both horns

Cotyledonary Placenta

Species: Cow, Sheep (ruminants)

Feature: Rows of button-like caruncles on uterine wall

Numbers: ~120 caruncles (cow); ~80 (sheep)

Placentome: Cotyledon (fetal) + Caruncle (maternal) = exchange unit

By day 35, chorion distends into non-gravid horn

Zonary Placenta

Species: Dog, Cat (carnivores)

Feature: Villi form a complete or incomplete band (zone) around the chorion

Discoid Placenta

Species: Primates (humans), Rodents

Feature: Single disc-shaped area of exchange

B · Placental Structure (Layers) & Function

Placentas are also classified by the number of tissue layers separating maternal and fetal blood. Fewer layers = more intimate contact.

Epitheliochorial

Species: Livestock (pig, horse, cow, sheep)

Layers: Chorion + endometrium each have intact basement membranes separating capillary blood supply

Contact: Chorion and endometrium in contact — most barriers between fetal and maternal blood

Antibody transfer: None (pre-natal); colostrum essential post-birth

Endotheliochorial

Species: Dogs, Cats (carnivores)

Layers: Chorion in contact with the endometrial capillary endothelium

Antibody transfer: Limited (some pre-natal)

Hemochorial

Species: Rodents, Primates (humans)

Layers: Pool of maternal blood directly exposes chorion cells — most intimate contact

Antibody transfer: Extensive (significant pre-natal transfer)

Placental Functions

Nutrient Supply

Water exchange
Gas exchange (O₂ / CO₂)
Nutrient transfer (amino acids, glucose, fatty acids)

Barrier

Microbes (most cannot cross)
Large cells and proteins
Some drugs do cross (lipophilic)

Antibody Transfer (pre-natal)

None — Epitheliochorial (livestock)
Limited — Endotheliochorial (dog, cat)
Extensive — Hemochorial (rabbit, guinea pig, primates)

Extra-Embryonic Membranes

Conceptus = embryo/fetus + its membranes

Amnion — innermost fluid-filled membrane; cushions and hydrates fetus

Allantois — often fuses with chorion (allantochorion); fills with fluid; waste reservoir

Chorion — outermost membrane; attaches to uterus; site of villi/exchange

C · Placental Hormones & CL of Pregnancy

Steroid Hormones from Placenta

Progesterone (P4): Mid-to-late gestation; essential for uterine quiescence (suppresses contractions), uterine gland secretions, blood supply

Estrogen (E2): Increases late in gestation in several species (pig, cow); increases oxytocin receptor sensitivity for parturition contractions

Cortisol: Fetal cortisol increases late in gestation; triggers placental conversion of P4 → E2; signals parturition

Glycoprotein/Protein Hormones

hCG (human Chorionic Gonadotropin):

Produced by trophoblast from day 7 to ~day 70
LH activity in ALL species; stimulates CL to produce P4
Basis of early human pregnancy test (separated from female's urine)

eCG / PMSG (equine Chorionic Gonadotropin / Pregnant Mare Serum Gonadotropin):

Mare develops endometrial cups (~day 35–60) from trophoblast invasion
Cups produce eCG to grow/ovulate follicles → form accessory CL → ↑ P4
In other species: potent FSH-like activity used in superovulation

Relaxin: Found in humans, horses, cats, dogs, rabbits; remodels and softens cervix/birth canal for parturition

CL of Pregnancy

CL Maintained

For most of gestation, CL remains active and needed for P4
Luteolysis is blocked by embryonic signals (maternal recognition of pregnancy)
In cattle/sheep: interferon-tau blocks PGF₂α pulsatile release
In primates: hCG maintains CL

Placental Takeover of P4

Some species: placenta gradually assumes P4 production
Ewe: ~day 50 (early takeover)
Human/Horse: ~day 70
Cow: ~day 210 (late takeover)
P4 used clinically to prevent premature birth in women

D · Gestation Lengths & Species Details

Gestation Length by Species

Species	Length	P4 Takeover
Rat	21 days	—
Dog	≥64 days	—
Cat	64 days	—
Pig	115 days	—
Ewe (sheep)	150 days	~day 50
Cow	280 days	~day 210
Human	280 days (last period) / 268 days (ovulation)	~day 70
Horse	340 days	~day 70

Gestation length accuracy depends on knowing day of conception. Estimated from 1st day of last period (women) or first day of estrus/breeding (animals).

Conceptus Expansion & Fetal Positioning

Early Gestation Conceptus Expansion

All conceptuses expand within the uterine horns
Horse (d35): chorion forms extended oval, localized
Cow (d35): chorion distends into non-gravid horn
Litter species (pig): conceptuses spread to cover both horns

Fetal Positioning (months before birth)

Repositioning occurs via contractions toward cervix that rotate fetus
Cattle: ~95% anterior (head-first) by 6 months
Horses: Only ~40% anterior at 6 months — repositioning occurs later
Litter species: less critical — multiple fetuses delivered sequentially

E · Parturition & Postpartum Recovery

Parturition Overview

General term: Process of birth — sequence of events to expel fetus and membranes

Duration: ~2–5 hours (singleton); litter species birth at 15–60 min intervals

Species-specific terms:

Sheep: Lambing
Pig: Farrowing
Cow: Calving
Horse: Foaling
Dog: Whelping
Cat: Queening

Visual Symptoms of Approaching Birth

Weeks before:

Swelling of abdomen, vulva, and mammary gland
Relaxation of birth canal (pelvis/cervix)

Days/hours before:

Milk ejection (colostrum)
Mucus drip (cervical plug dissolves)
Anxious, restless, seeking isolation behaviors

Stage 1: Parturition Signal Cascade

Fetal Initiation of Signal

Fetal hypothalamus/pituitary responds to physiological stress (crowding, hypoxia)
Fetal ACTH released → fetal adrenal produces cortisol
Cortisol causes placenta to convert P4 → E2
↑ Placental E2: increases oxytocin receptors in myometrium, cervix relaxation, stimulates PGF₂α production
PGF₂α: induces CL luteolysis (or ends placental P4); removes P4 block on contractions
↑ Oxytocin + ↑ PGF₂α → uterine contractions escalate

Three Stages of Parturition

Stage 1: Removal of myometrial block (P4 falls, cervix dilates, mild contractions begin)

Stage 2: Fetus expulsion (strong contractions; membranes rupture; fetus delivered)

Stage 3: Placenta (fetal membranes) expulsion; retained placenta = complication in cattle

Postpartum Recovery

Uterine involution (return to pre-pregnant size)
Return to cycling: varies by species, nutrition, lactation
Lactation suppresses GnRH → postpartum anestrus
Weaning restores GnRH pulse frequency and return to estrus

Lecture 20Puberty, Seasonal Reproduction and Female Mating Behavior

A · Puberty

Definition & Importance

Why is puberty important?

Longest phase of infertility in an animal's productive life
First indication of breeding capability

Prepubertal: Immature ovaries, uterus, and neuroendocrine function

Pubertal (at puberty):

Reproductive system functional
Body size capable of sustaining gestation
Full range of sexual behaviors expressed
Still growing — rapid growth and large size NOT desirable for breeding longevity

Body weight threshold: Puberty reached at approximately 2/3 (60–70%) of mature body weight

Age at Puberty by Species

Species	Age at Puberty
Rat	~3 months
Chicken	~5 months
Sheep, Goats, Swine	6–7 months
Dog	6–24 months
Cat	6–10 months
Cattle	~12 months
Horses	~16 months
Rhesus monkey	2–3 years
Gorilla	6–8 years
Chimpanzee	7–11 years
Women (menarche)	~12.5 years (decreased ~5 yr since 1920)

Hormonal Control of Puberty

Prepubertal

Limited GnRH and LH release (low pulse frequency)
Small follicles producing low estrogen
Positive estrogen feedback not yet developed
Hypothalamus very sensitive to E2 negative feedback

At Puberty

Neuroendocrine system matures
Hypothalamus loses extreme sensitivity to E2 negative feedback
Hypothalamus responds to positive estrogen feedback → LH surge possible
↑ FSH and LH pulses → follicle growth → ovulation

B · Seasonal Reproductive Cycles & Photoperiod

Why Seasonal?

Farther from the equator → more wild species exhibit seasonal reproduction
Respond to photoperiod (day/night length ratio) and temperature
Change fertility with seasons: cycle between anestrus (non-breeding) and estrus (breeding)
Equator = hot, humid, no distinct seasons → year-round reproduction common

Melatonin & Photoperiod

Light sensed through eye → neural signal → pineal gland → melatonin

Melatonin is released at night (darkness)

Long nights (short days) → more melatonin
Short nights (long days) → less melatonin

Melatonin + RFRP-3 act together to induce or inhibit GnRH release

Cascade: Melatonin → GnRH → FSH → LH → ovulation (or suppression, depending on species)

Seasonal Breeding Species

Species	Type	Breeds During
Horse (mare)	Long-day breeder	Spring/Summer
Sheep (ewe)	Short-day breeder	Autumn/Winter
Cat	Long-day breeder	Spring/Summer

Species have opposite responses to melatonin — horses and sheep respond differently to the same melatonin signal.

Using Light to Manipulate Reproduction

Horses (Northern Hemisphere):

Increasing artificial light by 30 min/week starting in late December
Advances onset of spring estrus and ovulation
Allows breeding earlier in the season (e.g., for January 1 birth dates in Thoroughbreds)

Melatonin implants are used in sheep to advance the breeding season similarly.

C · Female Neuroendocrine Development & Estrus Behavior

Development of Female HPX Axis

Originates during fetal/neonatal period — critical window for sexual differentiation of the brain

Female (XX):

Placental estrogen is present
AFP (Alpha-Fetal Protein) produced by fetal liver binds estrogen
AFP + estrogen complex is too large to cross the blood-brain barrier (BBB)
→ Female hypothalamus-pituitary axis (HPX) develops by default (cyclic/feminine)

Male (XY) — De-feminization:

Fetal testes produce testosterone
Testosterone crosses BBB (not bound by AFP)
Inside brain: testosterone is aromatized to estrogen
Estrogen acts on brain → de-feminizes HPX (eliminates cyclic LH surge capability)

Female Estrus & Mating Behavior

Estrus behavior: Induced by estrogen, prevented by progesterone

Estrogen increases before estrus in all species (including birds)

Types of Sexual Behaviors:

Proceptive — Active seeking of a mate; female approaches male; solicitation behaviors

Receptive — Stands to be mounted; lordosis (arched back, standing heat); the hallmark of estrus

Refractory — Period of refusal during or after estrus; female rejects mounting attempts

D · Mammalian Pheromones & Reproductive Behavior

Mammalian Pheromones

Structure: Small volatile steroids or fatty acids

Evidence in: Rodents, pigs, ruminants, horses

Sources: Vagina, urine, saliva, skin glands

Reception pathway:

VNO (Vomeronasal Organ) → ciliated neurons → olfactory bulb → modify hormones or behavior

Flehmen response in ungulates uses the VNO to detect pheromones

Pheromone Types:

Primer — Endocrine effect; stimulates puberty onset (e.g., male odor advances puberty)
Releaser — Immediate behavioral response (attractant; triggers standing heat)
Modulator — Mood/emotional effects (potential in humans)

Pheromone Effects & Mare Behavior

Rodent Pheromone Effects:

Bruce Effect: Introduction of a new male causes pregnancy termination (abortion) in recently mated female mice
Whitten Effect: Male odor synchronizes/advances estrous cycles in females housed together

Human Pheromones:

Limited evidence; no functional VNO confirmed
Women living together may show menstrual cycle synchrony

Reproductive Behavior in the Mare:

Heat detection via teasing with stallion
Receptive behaviors: excited, raised tail, frequent urination, winking (clitoral exposure), vocalization, stands for mounting

A · Assessing Female Reproductive Status

Control of Female Fertility — What You Need to Know

Are they cycling?

Last known records for:

Estrus or menstrual period

Are they expected to be cycling?

Seasonal — is it the breeding season?
Age or weight (Puberty) — have they reached puberty?
Days post-partum — how recently did they give birth?

How to Obtain Reproductive Information

Animals: Domestic, Wild, or Captive — Livestock, Pets, Elephant, rhino, large cats, bears, deer

Methods:

Observation for Behaviors — Domestic aids: patches, chalk, electronics, cameras
Scanning of Ovaries — Holding chute or Sedative?
Blood/feces progesterone — need lab processing
Saliva/urine progesterone — dip stick tests (species specific?)

FYI: Measuring Fertility in Women — Home ELISA-Based Tests

Menopause / Ovarian Reserve

Hormone: FSH / AMH
High AMH → many follicles remaining
High FSH → low reserve (menopause approaching)

Pregnancy Test

Hormone: hCG
hCG produced by implanting embryo/placenta
Urine or saliva

Ovulation Test

Hormone: LH
Detects the preovulatory LH surge in urine
Identifies optimal breeding window

B · Inhibition of Fertility

Three Options for Reproductive Control

Inhibition

Humans — birth control pills, implants, patches
Animal population control: dogs, cats, horses, feedlot, wild

Induction

Induce a timed breeding event
Used for: puberty, seasonal anestrus, post-partum anestrus, controlled breeding

Synchronization

Synchronization of group animal breeding for timed AI

Inhibition of Fertility — Mechanisms

Prevent Final Follicle Maturation & Ovulation:

Limit GnRH and LH
FYI: Morning after pills are labeled to prevent ovulation

Progesterone:

Oral in feed or implants for animals
Pills, implants, or patch for humans

Immunization against GnRH:

Prevents need for castration

FYI Challenges:

Daily dosing required (humans and animals)
Capturing and treating animals in the field

Suppression of Fertility in Cats & Dogs

Overpopulation of feral pets is a serious problem

Options:

Surgical spaying or neutering — requires surgical space, time, and cost
Progestin treatment — oral (dosing) or implants; effective but impractical for feral animals
Vaccines to reproductive hormones — GnRH most studied and practical; effectiveness declines over time after injection

FYI: Control of Dog/Cat Reproduction

Ovaban (Megestrol Acetate / MGA):

Oral progestagen fed to dogs over multiple days
Suppresses cycling via negative feedback on GnRH/LH

Mibolerone (Cheque):

An androgen given in food once (liquid applied)
Works via negative feedback on GnRH/LH
Effective for preventing estrus in dogs

C · Birth Control in Women — Progesterone-Based Options

Options for Birth Control in Women (Based on Progesterone)

Form	Dose Freq.	Hormone	Actions	Cycles/Period?
Pill	Daily	E + P (21d) + 7 Placebo	Blocks ovulation; thick mucus	Yes
Mini Pill	Daily	P (21d) + 7 Placebo	Mucus thick	Yes
Depo Provera	1× / 3 mo.	P	Mucus, ovulation, endometrium	No
Patch (Ortho Evra)	1× / week	P + E	Mucus, ovulation, endometrium	No
NuvaRing (vaginal)	1× / mo.	E + P	Mucus, ovulation, uterus (thin)	No
IUD Mirena	1× (long-term)	P — also non-hormone options	Prevents sperm transport / uterine implant	No
Implanon (implant)	1× / 3 yr	P	Ovulation, mucus, endometrium	No

Example: Patch (Ortho Evra) & Pill (Extended Cycle Yasmin)

Ortho Evra Patch:

E + P delivered transdermally
3 patches during weeks 1–3
No patch in week 4 (withdrawal bleed)

Extended Cycle Yasmin:

28 days of E + P active pills
Then 7 days of placebo (period)

Rationale for Sequencing:

During P4 dose weeks: No follicle selection or ovulation (constant negative feedback on GnRH/LH)
During Placebo week: Hormone withdrawal → uterine lining sheds (withdrawal bleed/period)

Key concept: everything works via progesterone-driven negative feedback on the HPG axis.

D · Inducing Fertility & Estrus Synchronization

Inducing Fertility

Goal: Start a follicle phase (PROESTRUS)

Estrus → Breed → Pregnancy → Offspring

What Works?

Animals: eCG (equine CG) — FSH-like activity; long half-life → effective with single injection
Humans: Recombinant FSH / LH — short half-life; repeated injections required (used in IVF/ART)

eCG is produced by the endometrial cups of pregnant mares and has both FSH and LH activity.

Livestock Estrus Synchronization

Goal: Synchronize one or a group of randomly cycling animals

Progesterone is Key:

Exogenous progesterone simulates the luteal phase
Suppresses follicle phase (no ovulation during treatment)
Withdrawal → synchronous follicle phase begins across all animals simultaneously
Allows timed AI (artificial insemination) without needing to detect estrus

Simple Example: Pigs & Horses — Progestogen Feeding Protocol

Why Pigs & Horses?

These species only have a large dominant follicle during the follicle phase
To synchronize ovulation, need to synchronize when the follicle phase starts
Feed a synthetic progestogen orally for the luteal phase → creates artificial progesterone exposure

Protocol:

Feed progestogen for 14 days to randomly cycling animals
Stop feeding → progesterone withdrawal
All animals enter a synchronous follicle phase ~4–6 days later
Peak estrus/ovulation surge observed ~day 18–20 after feeding started

Commercial Products:

Matrix

Oral progestogen for pigs (altrenogest in feed)

Regu-Mate

Altrenogest liquid for horses (applied to feed; requires protective gloves)

Note: Altrenogest (Regu-Mate) is hazardous to women — absorbed transdermally; handle with gloves.

E · Infertility, Reproductive Tract Defects & Infectious Diseases

Types of Infertility

Non-Infectious:

Anestrus: Season, stress, disease, old age, truly infertile
Conception failure: Sperm/egg defects, poor AI timing, reproductive tract defect

Infectious:

Viral — parvovirus, herpesvirus
Bacterial — leptospirosis, brucellosis

Twinning & Freemartin

Twinning (not infertility):

Dizygotic: 2 different eggs (90% of twins); fraternal — same or different sex
Monozygotic: 1 egg splits; identical — same sex; splits during blastocyst formation (can lead to conjoined twins)
Desirability varies by species — undesirable in horses

Freemartin (cattle):

Heifer born co-twin to a bull
Female is sterile (XX masculinized)
Cause: Placentas fuse → shared blood → male androgens from fetal testes masculinize female reproductive tract development
Documented primarily in cattle; rare in sheep

Non-Infectious Reproductive Tract Defects

Prolapse (more common in cattle):

Types: Uterine, cervical, vaginal
FYI: Genetic and body condition factors
Post-partum, associated with dystocia
Treatment: Cleaning and sewing vulva lips; high risk to repeat

Cystic Ovarian Disease (COD):

Persistent follicles that keep growing without ovulating
~20% of dairy cows; Women: PCOS (Poly Cystic Ovarian Syndrome)
Signs: Anestrus, irregular cycles, discomfort/pain
Treatment: GnRH in cows; birth control pills in women

Endometritis / Pyometra:

Inflammation or infection of uterus (endometrium = endo; myometrium = metritis)
Fluid accumulation, discharge, fever
Most common post-partum in cattle, mares, and dogs
Causes: Poor tract structure, hygiene, dystocia
Treatment: Antibiotics, Prostaglandins

Infectious Diseases Affecting Reproduction

Viral:

Parvovirus — causes abortion in pigs; vaccine available
Herpesvirus — Dogs (CHV: abortion, neonatal death), Horses, Cats; Cows (IBR — Infectious Bovine Rhinotracheitis)

Bacterial:

Leptospirosis (common) — Zoonotic; livestock, dogs; spread via animal fluids/contaminated water/floods; causes abortion; vaccine available but many strains
Brucellosis (common) — Zoonotic; from animals and products (milk); abortion in cattle, sheep, dogs; vaccine available

Prevention Strategies:

Biosecurity, Vaccination, Eradication programs
Dog vaccines include: rabies, distemper, hepatitis, parvo, lepto

A · Poultry Reproduction

Poultry — Key Differences from Mammals

Cycle type: Ovulatory cycle — no estrus or estrous cycle

No: Corpus luteum, luteal phase, or pregnancy (egg-laying)

Anatomy:

Left ovary and left oviduct are the only functional side
Right oviduct is undeveloped or non-functional

Timeline:

Ovulation → oviposition (egg laying) ~ 26 hours
Incubation: 21 days

Chicken Ovulatory Cycle — Photoperiod Control

Photoperiod-responsive: Natural or artificial light (on and off) regulates the cycle

Timed example (lights off at 6 PM):

6:00 PM→ Lights off

12:00 AM→ LH surge

6:00 AM→ Ovulation (F₁ follicle / oocyte)

Light management in commercial poultry production uses this principle to control laying frequency.

B · Deer & Carnivores (Lions/Tigers)

North American White-Tailed Deer

Classification	Ruminant
Cycle length	~22 days; estrus 18 hours
Uterus / Placenta	Bicornuate; Cotyledonary
Breeding pattern	Seasonally polyestrus — Oct–Nov (short-day breeder)
Birth season	May–June; gestation 205 days
Puberty / First breed	~6 months puberty; breeds at +1 year old in fall
First offspring	1 fawn at 2 years old
Twinning	>parity = twins (more likely with increasing pregnancies)

Carnivores — Lions & Tigers

Puberty	~3–5 years
Seasonality	Non-seasonal
Estrus	5 days; matings every ½ hour
Ovulation type	Induced ovulators
Placenta	Zonary (carnivore type)
Gestation	104–110 days
Litter size	2–4 cubs
Others	Cheetah, Leopard, Jaguar, Panther: 93–105 days

C · Non-Human Primates & Exam Framework

Non-Human Primates

Seasonality: Non-seasonal

Cycle type: Menstrual cycle (not estrous)

Species	Cycle Length	Gestation
Gorilla	45 days	225 days
Chimpanzee	35 days	—
Orangutan	28–32 days	258 days

Key features:

In heat 1–2 days only, or no estrus* (reduced estrous behavior)
Uterus simplex (single undivided uterine body)
Placenta: Discoid, hemochorial — maternal blood contacts fetal trophoblast; antibodies can be shared
*hCG test works for pregnancy detection

Exam Framework: Comparing Species to Model Species

For each species, assess similarity to our model species (cattle, pig, horse, sheep) across 4 criteria:

1. Cycle Length

How long is their estrous/menstrual cycle?

2. Spontaneous or Induced Ovulation

Does ovulation occur automatically (spontaneous) or only after mating (induced)?

3. Seasonal Breeding

Does the species only breed at a specific time of year?

4. Gestation Length

How long is the pregnancy? Reflects offspring development strategy.

Lec 13–14

Lec 15–17

Lec 18–20

Lec 21–22