Estrous Cycles and Terminology Lecture 18

A comprehensive set of vocabulary flashcards covering the hormonal control, stages, and species-specific differences of estrous cycles as well as pregnancy recognition factors and reproductive behaviors.

Proestrus

The stage of the estrous cycle characterized by decreasing $P4$, increasing $GnRH$, $FSH$, and $LH$, and a significant rise in estradiol ($E2$) produced by developing follicles.

Estrus

The period of behavioral receptivity ('standing heat') during which estradiol ($E2$) reaches a threshold level to trigger the pre-ovulatory $LH$ surge leading to ovulation.

Metestrus

The stage following ovulation where the major source of $E2$ is lost and the follicle undergoes luteinization to form the corpus luteum ($CL$), leading to an increase in $P4$.

Diestrus

The longest stage of the estrous cycle, characterized by a fully functional corpus luteum ($CL$) and high concentrations of progesterone ($P4$).

Luteolysis

The regression of the corpus luteum ($CL$) induced by PGF2a from the uterus in the absence of an embryo, resulting in a drop in progesterone ($P4$).

Polyestrus

Species that cycle continuously throughout the year, such as the cow, sow, and rodents.

Seasonally Polyestrus (Long Day)

Species that begin to cycle as day length increases in the spring, specifically the mare and the feline queen.

Seasonally Polyestrus (Short Day)

Species that begin to cycle as day length decreases in the autumn, such as the ewe, doe, and nanny goat.

Monestrus

Species that typically have only one estrous cycle per year, such as the bitch, other canids, and the bear.

Induced Ovulator

Animals that require the stimulus of mating to trigger ovulation, including the llama, queen, and South American Camelids ($SAC$).

Local Pathway (Luteolysis)

A mechanism in ruminants where PGF2a is transported directly from the uteroovarian vein to the ovarian artery due to their close juxtaposition, reaching the $CL$ without entering systemic circulation.

Systemic Pathway (Luteolysis)

The mechanism in the mare where PGF2a released from the endometrium travels through systemic and pulmonary circulations to reach the $CL$.

Interferon tau (IFN-tau )

The specific pregnancy recognition factor released by the embryo in sheep and cattle to prevent luteolysis.

Luteotrophic

A substance that maintains or protects the corpus luteum, such as estrogens in swine and prolactin in dogs.

Anestrus

A period of reproductive quiescence between cycles, which in the bitch lasts approximately $90$ to $150$ days.

Attractivity

The first stage of female reproductive behavior involving signals like postures, vocalizations, and pheromones to attract the male.

Proceptivity

The second stage of female reproductive behavior consisting of specific behaviors exhibited to stimulate male mating behavior.

Receptivity

The final stage of female reproductive behavior, often called 'standing heat,' characterized by immobility and lordosis.

Lordosis

A specific mating posture exhibited by a queen or bitch as a sign of behavioral receptivity.

Equine Chorionic Gonadotropin ($eCG$)

A hormone produced by endometrial cups in the pregnant mare that helps maintain the primary $CL$ and induces the formation of secondary $CL$s to support pregnancy.

Cow Estrous Cycle

A cycle with an average duration of $21\,d$ and an estrus duration of $18\,h$, with ovulation occurring $24$ to $30\,h$ after the onset of estrus.

Bitch Estrous Cycle

A monestrus cycle with a $9\,d$ proestrus and a $9\,d$ estrus; ovulation of a primary oocyte occurs $2$ to $3\,d$ after the $LH$ surge.

5a-pregnanes

The primary progestogens of uterofetoplacental origin that maintain pregnancy in the mare from approximately day $100$ to $120$ of gestation.

Pregnancy Recognition in Swine

A process triggered by the embryonic release of Estradiol ($E2$) between days $11$ and $12$ after ovulation.

Pulmonary Metabolism of PGF2a

The breakdown of prostaglandin in the lungs; it is more extensive in ruminants than in horses, necessitating higher exogenous doses for cattle.