89. Phases of the estrus cycle, species specificities in the sexual cycle

Question 1

Define Estrous cycle:

Answer 1

Estrous cycle is the period between two consecutive ovulations.

Question 2

There are four distinct stages of the estrous cycle:

Answer 2

• proestrus, estrus, metestrus and diestrus.

* Lack of estrus cycle is called: anestrus.

Question 3

Length of Estrus

Answer 3

Length of Estrus is generally 21 days:

• Sheep: 17 days
• Cat: 10 – 22 days
• Dog: ~2 months
• Human: 28 days

Question 4

Phases based on the ovarian functions:

Answer 4

• Follicular phase
• Ovulatory phase
• Luteal phase

Question 5

Explain shortly about the three phases:

Answer 5

Phase 1:Follicular phase (days) Period of follicle development
(dominated by E2 of the follicle; initiating sexual receptivity)
Phase 2: Ovulatory phase (minutes)
Phase 3: Luteal phase (days)(dominated by P4)
Period when corpus luteum is active.

Question 6

Give a general overview of proestrus, estrus, metestrus, diestrus and anestrus:

Answer 6

Proestrus
• End of the follicular maturation, fast growth of the dominant follicle. E2 level increasing, but the female, however, is not yet ready for copulation.

Estrus
• Sexual receptivity with all the necessary
morphological and behavioral changes (high E2)

Metestrus
• After the estrus, rising P4 concentration (CL)

Diestrus
• The longest part of the estrous cycle, high P4 level

Anestrus
• sexual inactivity (seasonal even, during lactation,
pathological conditions)

Question 7

Anestrus

Answer 7

Anestrus is an interval of sexual inactivity between two periods of estrus in female mammals that breed cyclically
This is typically a seasonal event and controlled by light exposure through the pineal gland that releases melatonin.
• Melatonin may repress stimulation of reproduction in long-day breeders.
Anestrus is also induced by pregnancy, lactation, or some pathological condition (such as significant illness, chronic energy deficit, etc.)

Question 8

What are the species differences?

Answer 8

1. Selection of dominant follicles in large animals
2. Length of cycle
   • primatesvsfarmanimals
3. Types of estruses
   • Continuous vs seasonal animals
   • Induced vs spontaneous ovulators

Question 9

What is one of the causes of the cycle lengths considerable difference?

Answer 9

in the primate the follicular and luteal phases follow each other sequentially. In domestic animals groups of follicles start to grow periodically and a “dominant follicle” is selected (as discussed in detail), which processes effectively shorten the entire length of the cycle. The mature “dominant follicle”
is more developed at the end of the luteal phase and it is also
closer to a possible ovulation, that in the primate.