Resumption of ovarian activity Flashcards
Are the following inhibitory or stimulatory on the HPG axis: Melatonin Oestradiol from the antral follicle Offspring Prolactin Progesterone from the CL Negative energy balance
Melatonin - can be both acts at the hypothalamus
Oestradiol from the antral follicle - can be both, acts at hypothalamus and inhibits at the pituitary
Offspring - inhibits at the hypothalamus
Prolactin- inhibits at the hypothalamus
Progesterone from the CL - inhibits at the hypothalamus
Negative energy balance - inhibits throughout
Which types of sheep can breed in Oct-Feb and July-March?
Dorset and merino
They have a lower depth of anoestrus or melatonin receptor defects
Describe the transition period of the mare after anoestrus
Takes 50-60 days of Irregular oestrus
Transition follicles and Low oestradiol
There is increased GnRH which increases FSH but not LH, this is enough to initiate antral folliculogenesis but slowly the LH rises and ovulation as normal will occur.
How can we manipulate seasonality?
Physical change to photoperiod
E.g. “shuttle” stallions from North to South hemispheres
Artificial change to photoperiod
E.g. Put mare under lights at Christmas
How does the breeding season of mares at the equator differ?
Breeding season shorter as distance from equator increases
Mares in equatorial regions have prolonged breeding seasons which approach polyoestrous
What is Anoestrus during gestation caused by?
Prolonged, high progesterone
How long does uterine involution and resumption of ovarian activity take in the beef cow?
Uterine involution - 30 d
Resumption of ovarian activity - 50-60 d
How long does uterine involution and resumption of ovarian activity take in the dairy cow?
Uterine involution - 35-40 d
Resumption of ovarian activity - 18-25 d
How long does uterine involution and resumption of ovarian activity take in the bitch?
Uterine involution - 90 d
Resumption of ovarian activity - 135 d
How long does uterine involution and resumption of ovarian activity take in the ewe?
Uterine involution - 30 d
Resumption of ovarian activity - 180 d
How long does uterine involution and resumption of ovarian activity take in the mare?
Uterine involution - 14 d
Resumption of ovarian activity - 5-12 d
How long does uterine involution and resumption of ovarian activity take in the queen?
Uterine involution - 30 d
Resumption of ovarian activity - variable
How long does uterine involution and resumption of ovarian activity take in the sow?
Uterine involution - 28- 30 d
Resumption of ovarian activity - 21-28 d
What is the purpose of post-partum anoestrus?
To allow uterine involution, Lactation/suckling and for CL from pregnancy will regress.
Describe the return to cyclicity post-partum
Initially pituitary has refactoriness to GnRH but allows FSH secretion (low E2 / P4) which causes follicular wave emergence
There is Increasing sensitivity to GnRH, Increased oestradiol, Increased LH pulse frequency which leads to Ovulation (normally silent oestrus or Short oestrous cycle)
