Applied Mare Reproductive Physiology Flashcards
describe the equine estrous cycle
- ovulation is day 0; the cycle is 21 days long and has two phases: estrus and diestrus
-seasonal polyestrous - FSH is high at the beginning of estrus and induces follicular growth
- growing follicles produce estradiol and inhibin which inhibit FSH release
- large follicles grow on the ovaries and produce estradiol which induces sexual receptivity
- estradiol induces the peak of LH
- ovulation occurs 1-2 days before the end of estrus
- LH reaches maximum concentration after ovulation (unique to mares, other species have peak LH during ovulation)
- a corpus luteum forms after ovulation and produces progesterone which inhibits sexual receptivity
- the endometrium releases PGF2alpa on day 14 of the cycle, which lyses the CL and terminates diestrus
describe methods of estrus detection
- teasing: (most common in the clinical setting) evaluates the reaction of the mare to the stallion; safety is sexy! use tease rail or stall teasing, don’t just let them go at it
-if in diestrus: mare will move away, hold ears back, swish tail, kick, bite, paw, and vocalize
-if in estrus: mare will approach the stallion, remain calm, have a relaxed facial expression, raise her tail, posture, urinate, wink, and lean towards the stallion
- ultrasound:
-estrus: follicle present, preovulatory will be 35-60mm, uterine edema (from estrogens), relaxed cervix
-diestrus: corpus luteum present, no uterine edema, closed cervix
- vaginal exam
describe the intensity of estrous behavior throughout the cycle
begin more timid as come into heat, increases as get closer to ovulation
describe requirements for mating and estrus expression (3)
- mare-stallion bond
- peak of estrus
- no distractions
describe what is wrong with many modern mating practices (4)
- teased by the wrong stallion
- no time or space for interaction
- no intimacy
- restraint associated with fear
describe the primary versus secondary follicular wave
primary follicular wave: emerges on day 9 (mid-diestrus) and results in ovulation
-all mares have primary waves!!
secondary follicular wave: some mares have, emerges around ovulation, produces estrogen but progesterone still high enough to suppress LH release so follicle will eventually regress and stop producing estradiol so primary wave can grow
-can have a dominant follicle during diestrus together with a CL
-DOMINANT FOLLICLE DOES NOT MEAN ESTRUS!!
describe when a mare’s cycle begins and throughout her life
cycle from puberty to senescence
cycle begins at puberty: once reach 60-70% of adult body weight
ovarian activity ceases at 25 years
-produce smaller and smaller follicles as age until stop cycling
what 3 physiological conditions interrupt estrous cycles?
- season
- pregnancy
- lactation
what is the goal of mare seasonality?
to give birth when weather conditions are optimal and food is abundant
describe birthing season versus breeding season
spring is goal birthing season, gestation is 340 days, so breeding season is the prior spring (long-day breeders)
describe regulation of the foaling season (3)
- seasonal ovarian activity
- gestation length: longer in early bred mares
- post-partum anestrus: longer in early bred mares
-don’t tend to have otherwise
how do horses synchronize repro events with season?
- photoperiod!!!
-number of hours of daylight
-main cue that regulates seasonality - temperature
- nutrition
describe winter anestrus in mares
- the pineal gland secretes melatonin during darkness
- melatonin inhibits GnRH secretion from hypothalamus
- without GnRH there is no FHS or LH
- without FSH or LH there is no follicular growth or ovulation, so no estrogen production or estrous behavior
- this happens between november to january
describe spring transition in the mare
- light is detected by photoreceptors in the retina
- via sympathetic nerves, light inhibits melatonin synthesis
- with more hours of light there is less melatonin in the spring
- decreased melatonin allows for reactivation of GnRH secretion
- with increasing GnRH, FSH is released first
- FSH induces initiation of follicular waves
- mares show estrous behavior and follicular growth, but no ovulation
- after 3-4 waves, follicles produce enough estrogens to induce a peak of LH and LH induces the first ovulation of the year (entering the breeding season)
- transition occurs between february to march and takes approx 60d to enter breeding season/ovulation
-first ovulation usually in first week of april and mare displays estrous cycles april to october
describe the effect of temperature on cyclicity
- high temp induces release of prolactin from pituitary
- prolactin induces expression of LH and FSH receptors on ovaries
- ovaries become more responsive to the increasing concentrations of FSH and LH
