Resumption of Ovarian Activity

Question 1

What is ovarian rebound?

Answer 1

Return to cyclicity post-partum, ovarian activity slows down during pregnancy and needs to be reactivated

Question 2

What are the controlling factors of seasonality?

Answer 2

Photoperiod, melatonin, temperature, nutrition, altered reproductive status

Question 3

What are the effects of FSH and LH?

Answer 3

FSH – follicular recruitment/growth, oestrogen production

LH – follicular dominance, ovulation, production of oestrogen & progesterone

Question 4

Why are some ewes able to breed for an extended period of time?

Answer 4

Lower depth of anoestrus, melatonin receptor defects, variation in size of pineal gland

Question 5

How is anoestrus maintained during gestation and post-partum?

Answer 5

Gestation – prolonged, high progesterone
Post-partum – uterine involution, lactation/suckling (produces prolactin), ovarian inactivity (period of low progesterone and low oestradiol)

Question 6

What are the mechanisms of ovarian rebound?

Answer 6

Reinitiation of the HPO axis (follicular wave emergence), resumption of full ovarian activity, uterine and metabolic influences

Question 7

Describe ovarian rebound in the main species

Answer 7

Mare – rapid onset, rapid uterine involution, foal heat by day 5-9 PP
Sow – profound suckling, then weaning effects, prolactin suppresses LH, short lactations result in longer weaning to ovulation intervals
Dog – period of reproductive quiescence which is not lactational, strongly influenced by nutrition/condition
Cat – oestrus is often inhibited by lactation, early weaning hastens onset of oestrus

Question 8

What are the major influences on anoestrus?

Answer 8

Suckling, peri-parturient abnormalities, milk yield/nutrition, parity, season, climate

Question 9

In the ideal cow, how long does anoestrus last and by what cycle is she pregnant?

Answer 9

Anoestrus lasts 20 days followed by short cycle, pregnant by 3rd cycle

Question 10

What problems can affect this?

Answer 10

Persistent CL, delayed ovulation, cessation of ovarian activity after initial resumption

Question 11

What strategies can be used to advance or delay puberty in domestic animals?

Answer 11

Nutrition, hybrid vigour by cross breeding, photoperiod & endocrine studies (GnRH & eCG)