Chapter 7: Estrous Cycle

Lecture 10

What does heat ensure?

Mating around the time of ovulation

When does sexual receptivity occur?

1st half of the cycle, before ovulation

What happens if there is no conception during an estrous cycle?

Another estrous cycle begins

What happens if there is conception during an estrous cycle?

A period of anestrous begins and estrous cycles cease

Estrus (noun) refers to

Heat

Estrous (adjective) refers to

The cycle itself, a description word

Season means…

A period when several estrous cycles can occur, “coming into season” = signs of estrus

What is an example of a polyestrous species?

cow, queen, pig, rodents

What is an examples of a polyestrous long day seasonal species?

Mare

What is an example of a polyestrous short day seasonal species?

Ewe, doe, elk, nanny

What is an example of a monoestrous species?

Dog, wolf, fox, bear

Why are dogs techncially not monoestrous?

Dogs go into heat 2 times every 3 years, about once every 9 months

Polyestrous species can get pregnant…

Any time of the yearW

Long day breeds mate when?

In the spring

Short day breeds mate when?

In the fall

Monoestrous breeds cycle…

One a year

The follicular phase typically takes up what percentage of the estrous cycle?

20%

The follicular phase begins…

When the corpus luteum regresses (stops P4 form being produced)

The follicular phase stops…

When ovulation occurs (stops E2 from being produced)

The main hormone during the follicular phase is…

Estrodial (E2)

During the follicular phase, what type of follicles dominate the ovary?

Antral follicles

The luteal phase begins…

When ovulation occurs

The luteal phase ends when…

The corpus luteum regresses

What percentage of the estrous cycle is spent in the luteal phase?

80%

What dominates the ovary during the luteal phase?

Corpora lutea

What is the main hormone during the luteal phase?

Progesterone (P4)

What are the 4 stages of the estrous cycle?

Proestrus, estrus, metestrus, and diestrus

One what day does implantation typically occur?

Day 7

What two stages of the estrous cycle are a part of the follicular phase?

Proestrus and estrus

What two stages of the estrous cycle are a part of the luteal phase?

Metestrus and diestrus

During proestrus, what is formed and what is secreted?

Follicles are formed, E2 is secreted

Proestrus starts with what event?

Luteolysis

What causes the transition into proestrus?

FSH/LH

How long does proestrus typically last in most species?

2-5 days

During proestrus, how does the hormone feedback system change?

From negative feedback to positive feedback

During Estrus, what is at its peak?

Sexual reciptivity, E2, and ovulation

What type of behaviors can be observed during estrus?

Proceptive and receptive behaviors

What are examples of receptive behaviors?

Lordosis and standing estrus

During what stage does mating occur?

Estrus

In sows/ewes, when does ovulation occur relative to estrus?

Mid/late estrus

In mares, when does ovulation occur relative to estrus?

1-2 days before the end of estrus

In cows/buffalo, when does ovulation occur relative to estrus?

10-12 hours after estrus

During metestrus, what is formed and what hormone is secreated?

Corpus luteum is formed and P4 is secreted

When does metestrus occur?

After ovulation

During metestrus, what two hormones are low?

E2 and P4 (2-5 days for P4)

Diestrus is characterized by the release of what hormone?

Sustained luteal secretion of P4

What is the longest state of the estrus cycle?

Diestrus

During diestrus, what hormone is high in concentration?

P4

How long does diestrus typically last?

10-14 days

Diestrus ends with what event?

Luteolysis

What stage of the estrus cycle do rodents lack?

Metestrus

What hormone keeps FSH from peaking in the rodent estrus cycle?

Inhibin

During anestrus, what happens to the ovaries?

Ovaries are inactive, no ovulatory follicules, and no corpus luteum

What hormone changes cause anestrus?

Low levels of GnRH, and therefore low FSH/LH

Anestrus is characterized by a period…

Of no regular estrous cycles

What can cause anestrus?

Pregnancy, lactation, poor nutrition, stress, pathology, and season

How does gestational anestrus happen?

High progesterone levels from the corpus luteum and placenta inhibit GnRH, which causes no FSH/LH to be released, which discontinues follicle growth and suppresses ovulation

What is the purpose of postpartum anestrus?

Time for uterine repair/recovery and protection from copulation induced infections

The length of postpatrum anestrus is dependent on…

The species

Lactational anestrus prevets…

A new pregnancy before young are weaned

What is the threshold of the amount of suckling sessions per day that allows for cyclicity to continue?

2

Why did seasonal anestrus develop?

To insure embryo/neonate survival

What two factors contribute to the resume of cyclicity in seasonal breeds?

Light and temperature

How long are typical long day breeder’s gestations?

1 year

In long day breeders, anestrus occurs during…

Winter

What is the purpose of waiting for the spring to give birth?

Increased nutrition available, better chance of survival

What is the gestation time of mares?

11 months

In short day breeders, anestrus occurs during…

Summer

After light reaches the eyebulb in a seasonal breed, what is the first thing to be activiated?

Suprachiasmatic nucleus

As daylight increases, RFRP-3 increases, and in short day breeds, this causes a ___ in kisspeptin.

Decrease

As daylight increases, RFRP-3 increases, and in long day breeds, this causes a ___ in kisspeptin

Increase

What is silent ovulation?

Ovulation without behavioral estrus

In ewes, when does silent ovulation occur?

1st cycle of the season

In cows, when does silent ovulation occur?

1st postpartum of ovulation

What causes silent ovulation?

Lack of progesterone from a previous ovulation

What does P4 do to the brain?

It primes it for increased sensitivity to E2

The cycle length of a cat is how many days?

17 days

If no copulation occurs in a polyestrus species…

A period of postestrus follows, there is no ovulation, no corpus luteum, no metestrus or diestrus

If mating occurs in a cat…

Ovulation is induced, the corpus luteum is formed, and P4 levels increase

The gestation period of a cat is…

60 days

In dogs, how long does proestrus and estrus last?

9 days each

What are charactaristics of proestrus in a dog?

Vaginal swelling, blood tinged discharge, E2 rises and peaks

What are charactaristics of estrus in dogs?

Period of reciptivity, FSH/LH peak, E2 decreases, and dominant follicles ovulate

How long is the period of anestrus in a dog and what causes it?

5 months, high levels of FSH

How long is diestrus in dogs?

2 months