reproductive function in horses Flashcards
Mare reproductive characteristics
puberty 12-24 months
seasonally polyestrus
stallion repro characteristics
puberty 4-5 years
functional year round- sperm numbers, ejaculate volume
season cycle
with winter solstice no cycling because less daylight
affect of daylight
perceived through optic N/ chasm
with sunlight pineal gland= decreased melatonin which acts on hypothalamus to increase GnRH acting on Ant. pituitary to increase FSH and LH which act on ovary to increase E2 and P4
throughout spring GnRH and LH accumulate
LH= maturation of follicle, induces estrogen production
collection of transitional equine follicles
have 3-4 waves of follicle production prior to mature release at estrus
ovarian characteristics in vernal transition
transitional ovary= not long enough to ovulate but have follicles present
behavior= prolonged heat- because follicles present but not ovulated then needs to stand to be bred when in heat
uterine characteristics in vernal transition
cervix, body and two hors
first ovulation in mare
corpus hemorhagicum- palpable and present for 24 hours
amount of LH needed for ovulation
universal birthdate
January 1st- in effort to unify and have horse not be young because of the universal bday want to breed when not ideal breeding season
breeding via AI
physiologic breeding season- april to september
operational breeding season- february to july
managing transition in breeding season
artificial lighting programs
stimulates daylight
accelerates time to first ovulation
does NOT shorten transition (estrous not shorter just shifted)- begin dec. 1 first ovulation feb. 15
summer
ovulatory receptive because of day length
long day= less melatonin
estrous cycle in mare
18-21 days
follicular phase- estrus (4-7 days)
luteal phase- diestrus (14 days)
follicular phase
largely function of daylight
estrus
large preovulatory follicle grows stimulating ovulation, which is ovulated decreasing estrogen
biphasic release of FSH- low degree prior to ovulation and 2nd in middle of cycle
estrogen and LH rise concurrently with preovulatory follicle during estrus phase
peak LH= post ovulation- not normal but has to do with fact that have follicles but not ovulating
luteal phase
dominated by CL
should remain constant
Diestrus
begins with ovulation (24-48 hrs) before end of estrus
corpus hemorrhagicum
CL- progesterone (pregnancy maintenance, if not pregnant PGF2a causes CL lysis so can re-enter heat)
estrus- follicular phase, follicles
dominant follicles- recruited early (8-10 mm) pre-ovulatory size large (40-50mm) produces estrogen (CS)
winking
+ sign of estrus
behavior in estrus
receptive
discharge and urination, winking
transracial ultrasound during estrus
edema within the uterine wall
urine- contains pheromones
cervical evaluation during estrus
no estrogen= pale pink, tight
as estrogen increases, will relax
ovulation in mare
equine, cortex inside and medulla surrounds
always ovulates through ovulation fossa, cannot palpate CL because of fossa
preovulatory follicle
means ready to breed the mare
maternal recognition of pregnancy
if not signaled endometrium releases so will cycle again because prostaglandin increases and progesterone decreases
diestrus behavior
not receptive, mare= violent
pale cervix, not relaxed
end product of estrus
14 days post breeding check to see if pregnant
if pregnant embryo signals to lumen for maternal recognition
fall transition
shorter days= increased melatonin
decreased GnRH
decreased LH and FSH
decreased estrogen and P4
unpredictable behavior
winter an estrous
equine industry- ambient temp imps. warmer can cycle longer
during transitional periods LH administration doesn’t always work
closer to equator see more round the year cycling
same hormonal effects as fall
ovary with no large preovulatory follicles present
conclusions
mare= seasonal breeders- long days initiate cyclicity
hormones drive the cycle- hypothalamic pituitary gonadal axis
seasonality affects both mares and stallions
reproductive function maximal during long days
mare- consistent cyclicity
stallion- increase sperm numbers and ejaculate volume
