Reproductive Cyclicity

What is estrus?

The period of sexual receptivity (heat) when the female accepts mating.

What is estrous?

An adjective describing the reproductive cycle (e.g., estrous cycle).

What defines an estrous cycle?

The predictable sequence of reproductive events from one estrus to the next.

What is anestrus?

A temporary period without regular estrous cycles.

What are the three classifications of reproductive cyclicity?

Polyestrous, seasonally polyestrous, and monoestrous.

What is polyestrous?

Repeated reproductive cycles throughout the year.

Which animals are polyestrous?

Cattle, swine, rodents, and domestic cats.

What is seasonally polyestrous?

Multiple reproductive cycles restricted to a particular breeding season.

Which animals are seasonally polyestrous?

Sheep, goats, horses, deer, elk, and wild cats.

What are long-day breeders?

Animals that begin cycling as day length increases.

Which animals are long-day breeders?

Horses and wild cats.

What are short-day breeders?

Animals that begin cycling as day length decreases.

Which animals are short-day breeders?

Sheep, goats, deer, and elk.

What is monoestrous?

Having approximately one reproductive cycle per year.

Which animals are monoestrous?

Dogs, wolves, foxes, and bears.

How frequently do domestic dogs typically cycle?

Approximately three cycles every two years.

What are the two phases of the estrous cycle?

Follicular and luteal.

What dominates the follicular phase?

Growing ovarian follicles and estrogen (E₂).

What dominates the luteal phase?

Corpus luteum (CL) and progesterone (P₄).

What percentage of the estrous cycle is follicular?

Approximately 20%.

What percentage of the estrous cycle is luteal?

Approximately 80%.

What are the four stages of the estrous cycle in order?

Proestrus → Estrus → Metestrus → Diestrus.

Which stages belong to the follicular phase?

Proestrus and estrus.

Which stages belong to the luteal phase?

Metestrus and diestrus.

What happens during proestrus?

Follicles grow, P₄ declines, and E₂ increases.

What happens during estrus?

Sexual receptivity, peak E₂, LH surge, and ovulation.

What happens during metestrus?

Ovulated follicle luteinizes and the CL begins forming.

What happens during diestrus?

Functional CL secretes sustained P₄.

What is the longest stage of the estrous cycle?

Diestrus.

What causes luteolysis in the lecture’s general estrous-cycle model?

Uterine prostaglandin F₂α (PGF₂α).

What is the reproductive cyclicity classification of dogs?

Monoestrous.

What are the stages of the dog’s cycle?

Anestrus → Proestrus → Estrus → Diestrus.

What stage is absent from the dog’s cycle in your lecture?

Metestrus.

How long is dog anestrus approximately?

20 weeks.

How long is dog proestrus approximately?

Nine days.

What physical signs characterize dog proestrus?

Blood-tinged vaginal discharge and vulvar swelling.

What happens hormonally during dog proestrus?

Follicles grow and E₂ increases, peaking before estrus.

When does ovulation occur in the dog?

Approximately days 2–3 of estrus.

What type of oocyte does the dog ovulate?

Primary oocyte.

Why is fertilization delayed in dogs?

The primary oocyte must complete maturation after ovulation.

How long after ovulation can fertilization occur in dogs?

Approximately 48–72 hours.

What is superfecundation?

Fertilization of different ova by sperm from different males, producing a mixed-sire litter.

Why can nonpregnant dogs experience pseudopregnancy?

Pregnant and nonpregnant dogs undergo similar P₄-dominant diestrus.

Does pregnancy alter the length of diestrus in dogs?

No, according to your lecture.

What type of reproductive cyclicity do domestic cats exhibit?

Polyestrous.

Are cats spontaneous or induced ovulators?

Induced ovulators.

What triggers ovulation in cats?

Copulation stimulates the GnRH → LH surge pathway.

How many copulations may be needed to induce an LH surge in cats?

Approximately 4–7, according to your lecture.

What happens after induced ovulation in cats?

CL formation and luteal activity.

What happens if a queen does not ovulate?

She remains in or returns to follicular cycling rather than forming a functional CL.

Can cats enter diestrus?

Yes, following ovulation and CL formation.

What is silent ovulation?

Ovulation without behavioral estrus.

Why is the first ovulation after anestrus often silent?

The brain has not received prior progesterone priming.

What is the function of progesterone priming?

It optimizes brain sensitivity to estrogen-induced reproductive behavior.

Why is the second ovulation after anestrus usually not silent?

P₄ from the first luteal period primes the brain for E₂-driven estrus.

Can ovulation occur without visible sexual receptivity?

Yes; this is silent ovulation.

What two factors regulate seasonal breeding?

Photoperiod and melatonin.

What happens to melatonin when darkness increases?

Melatonin secretion increases/lasts longer.

When do long-day breeders cycle?

During increasing day length, generally spring/summer.

When do short-day breeders cycle?

During decreasing day length, generally fall/winter.

What is the general seasonal reproductive pathway?

Photoperiod → melatonin signaling → GnRH → LH/FSH → ovarian activity.

What are major causes of anestrus?

Pregnancy, lactation, season, inadequate nutrition, stress, and disease.

What happens hormonally during anestrus?

GnRH ↓ → LH/FSH ↓ → minimal follicular growth and ovarian inactivity.

How does suckling affect reproductive activity?

Suppresses LH secretion, contributing to lactational anestrus.

What causes nutritional anestrus?

Inadequate energy/protein → decreased GnRH and gonadotropin secretion.