Reproduction Flashcards
mare begin pubert at…
can become pregnant at…
18 months
2 years old
equine estrous cycle
- seasonal polyestrus (long day breeders) between april and july
- estrous cycle is 21 days
- duration of estrus is 7 days
- ovulation occurs near end of estrus
estrus
- when mare shows sexual receptivity to stallions
- stronger signs as ovulation nears
- controlled by estrogen
- behaviour=raising tail, urination, posturing, winking
diestrus
- when mare rejects stallions
- 14-16 days, behaviour starts within 12 hours of ovulation
- controlled by progesterone
- behaviour=pins ears, clamps tail, switches tail, moves away, kicks
hormonal changes
estrogen, LH, and FSH high during estrus, with progesterone low; progesterone high and fsh, lh and estrogen low; FSH peaks twice at beginning and end of diestrus, and PGF2 spikes at end of estrus
hypothalamus
‘surge center’ where GnRh is released into pituitary gland and receives signals from ovary
-also commands release of LH and FSH from pituitary
pituitary
transport LH, FSH, and GnRH down to ovary
ovary and follicles
cause +ve feedback with hypothalamus or -ve with pituitary gland’s secretion of GnRH and FSH via inhibin
endocrinology of estrous cycle
GnRH stims FSH and LH from anterior pituitary
- FSH stims follicle development
- dominant follicle produces estradiol and inhibin
estrous cycle and estradiol, inhibin, and prostaglandin
estradiol=LH secretio, estradiol-receptor sensitivity on dominant follicle
- inhibin=decreased GnRH and FSH; leads to LH surge and ovulation
- prostaglandin (PGF2) causes lysis of CL and allows for ovulation
rule of thumb for estrogen/progesterone
high progesterone=suppresed LH
high estrogen=suppressed FSH
seasonality
transition periods in spring=vernal and fall=autumnal
- time of LOW reproductive activity, no clear patterns, and delayed ovulation
- normal cycles in april/may, september/october
- controlled by photoperiod
seasonality influences
age, body condition, disease
-2 years old cycle in june-august
-mares over 20 have few cycles in june or july or no ovary activity
over 25 seldom cycle
seasons for mares
summer=natural breeding season, fall transition, winter=anovulatory season, spring transition
photoperiod
controls ovarian activity through PINEAL gland and melatonin production