Estrus Detection, Estrous Cycles, and Synchronization

Vocabulary practice flashcards covering estrous cycle phases, follicular waves, hormonal mechanisms, estrus detection techniques across domestic species, and synchronization drugs.

Estrus Synchronization

The use of exogenous hormones to control or reschedule the timing of the estrous cycle, allowing tighter grouping of females for shorter breeding and parturition seasons and higher average weaning weights.

Follicular Phase

The portion of the estrous cycle consisting of proestrus and estrus, dominated by growing follicles and the production of estradiol ($E_2$).

Luteal Phase

The portion of the estrous cycle consisting of metestrus and diestrus, occurring after ovulation and dominated by the corpus luteum secreting progesterone ($P_4$).

Recruitment

The initial wave stage where a cohort of small, gonadotropin-sensitive follicles begins growing from the ovarian pool, visible on ultrasound as a group of small, equal-sized black dots.

Selection

The follicular wave stage following recruitment where a subset of follicles continues growing larger while the remaining follicles lag behind and begin atresia.

Dominance

The stage in a follicular wave where one or more selected follicles develop into large, fluid-filled structures that produce high levels of estradiol ($E_2$) and suppress smaller follicles.

Atresia

The degenerative process by which non-chosen follicles and oocytes fail to ovulate, beginning with breakdown of granulosa cells followed by resorption into the body.

Proestrus

The $1\text{ to }3\text{ day}$ stage immediately preceding estrus characterized by a gradual rise in estradiol ($E_2$) and a sharp decline in progesterone ($P_4$) following luteolysis.

Estrus

The period of sexual receptivity ('heat') driven by peak estradiol ($E_2$) and basal progesterone ($P_4$); ovulation occurs at the very end of this phase.

Metestrus

The post-ovulatory transitional phase where estradiol ($E_2$) decreases, progesterone ($P_4$) begins rising, and the ruptured follicle organizes into the developing corpus luteum.

Diestrus

The longest phase of the estrous cycle, characterized by a fully functional mature corpus luteum, maximal blood concentrations of progesterone ($P_4$), and minimum estradiol ($E_2$).

Prostaglandin $F_{2\alpha}$ ($\text{PGF}_{2\alpha}$)

The uterine luteolytic hormone released in episodic pulses from the endometrium that travels via counter-current transfer to the ovary to cause structural and functional regression of the corpus luteum.

Luteolysis Responsiveness Window

The physiological requirement that the corpus luteum must be at least $5\text{ to }6\text{ days}$ post-ovulation (fully mature) before it can respond to an injection of exogenous $\text{PGF}_{2\alpha}$.

Polyestrous

A reproductive cycle classification describing females that undergo continuous, recurring estrous cycles throughout the entire year without seasonal cessation (e.g., cows, sows, rats).

Seasonal Polyestrous

A reproductive pattern characterized by recurring estrous cycles restricted to a specific time of year, alternating with an anovulatory period (anestrus) regulated by day length.

Short-Day Breeders

Seasonal breeders (e.g., ewes and goats) that become sexually active as daylight decreases; increased darkness elevates melatonin, activating $Kiss1$ cells and stimulating the GnRH axis to initiate cyclicity.

Ewe Estrous Cycle Length

$17\text{ days}$, contrasting with cattle, swine, goats, and horses, which typically have a cycle length of $21\text{ days}$.

AM/PM Rule

The bovine breeding rule indicating that cows first observed in standing heat in the morning should be inseminated that afternoon, while those observed in the evening should be inseminated the next morning.

Teaser Animals

Intact-libido males that are surgically altered (e.g., vasectomized or gomer bulls) or androgenized females/steers used exclusively to identify females in heat without impregnating them.

Chinball Marker

A device fastened underneath the chin of a teaser bull that applies colored fluid to a cow's back or neck when the bull mounts and rests his chin on her.

Estrotect Heat Detector

A scratch-off patch applied to the tailhead of cows scored from $0$ to $2$; a patch with $>50\%$ of the coating rubbed off by mounting activity indicates standing heat ready for breeding.

HeatWatch

An electronic estrus detection system consisting of a pressure sensor mounted on the tailhead that wirelessly transmits mounting records and times directly to a computer via satellite/receiver.

Boar Exposure

The method of using the physical presence, sounds, and pheromonal smell of a mature boar to stimulate GnRH secretion and induce cyclicity in prepubertal gilts aged $160\text{--}180\text{ days}$.

Matrix

An orally active synthetic progestin administered in the feed to mature sows and gilts for $14\text{ days}$; females exhibit synchronized estrus $4\text{ to }9\text{ days}$ following its withdrawal.

Effective Weaning (Swine)

The practice of weaning entire litters of piglets at $21\text{ days}$ post-farrowing, which triggers sows to return to a synchronized estrus within $4\text{ to }10\text{ days}$.

CIDR (Controlled Internal Drug Release)

A T-shaped intravaginal insert that releases exogenous progesterone to mimic a corpus luteum, suppressing LH pulses and preventing ovulation until its removal.

MGA 200 Premix

A melengestrol acetate feed premix ($200\,\text{mg/lb}$) fed to feedlot and breeding heifers to suppress estrus and assist in estrus synchronization protocols.

ProstaMate

An injectable commercial $\text{PGF}_{2\alpha}$ analogue formulation containing $5\,\text{mg/mL}$ dinoprost tromethamine used to induce luteolysis in cattle, swine, and mares.

Cystorelin

An injectable commercial solution of synthetic GnRH (gonadorelin diacetate tetrahydrate, $50\,\mu\text{g/mL}$) administered to trigger an LH surge and induce ovulation.

Vulva Winking

A primary behavioral indicator of estrus in mares characterized by rhythmic contractions and eversion of the labia to expose the clitoris, typically accompanied by urination in the presence of a stallion.