Lecture 26

Question 1

What are the two main hormones that are secreted from the growing follicle in the oestrus cycle?

Answer 1

Oestrogen and androgen (females produce a small amount of androgens) but these can be transferred into oestrogen’s as well)

Question 2

Describe the basic stages of the oestrus cycle:

Answer 2

1. Proestrus (follicular growing phase)
2. Oestrus (display of male mating willingness will occur
3. Metoestrus- period just before ovulation occurs, not a fully functional corpus luteum will be present, it is just starting to develop and
4. dioestrous (luteal phase)

Question 3

What are the hormonal changes that occur in the proestrus phase?

Answer 3

This is a stage that involves follicular growth and maturation. Associated with increased amounts of oestrogen.

Question 4

What are the hormonal changes associated with oestrus?

Answer 4

Ovulation refers to the period where the female will allow the male to mate with her. An LH peak is stimulated and ovulation normally occurs around this time. The high levels of oestrogen causes a mechanism whereby it will switch from negative to positive feedback (this is why we get a surge in the LH hormone).

Question 5

What are the hormone changes that are associated with metoestrus and diestrus?

Answer 5

Met-oestrus is where ovulation has occurred and the corpus luteum is occuring. Dioestrus occurs where the corpus luteum is secreting progestorone

Question 6

What are the hormone changes that are occurring at the end of diestrus?

Answer 6

This is terminated by luteolysis (getting rid of the corpus luteum). The prostaglandin destroys the corpus luteum and hence stops the production of progesterone and removes the inhibition of FSH/LH. The next generation of follicles then grow to maturity and ovulate

Question 7

Differentiate between the terms oestrus and proestrous:

Answer 7

Oestrus simply means that the animal is in cycle, whereas anoestrous could be part of the cycle or potentially pathological

Question 8

How does melatonin regulate reproduction?

Answer 8

Melatonin release is stimulated by the activity of the supra-chiasmic nucleus (regulates circadian rhythms) that then projects to the retina. Increased melatonin secretion occurs with increased darkness, hence the internal signal relating to day length is set up by duration of night time secretion of melatonin.

Question 9

The cycling of ewes begins when the daylength _____

Answer 9

shortens

Question 10

The cycling of mares begins when the daylength ____

Answer 10

lengthens