Pharmacologic Control of Equine Reproduction Flashcards
describe natural versus artificial breeding season
natural: april to october-december
artificial: february to june, fixed by breed registry
-why hasten ovulation? january 1st as official birth date for competition horses; earlier foals are more mature at sales or shows
describe artificial lighting protocols to shorten time to ovulation
begin december 1st until spring or until ovulate, use 100lux at the end of the day (to lengthen the days), aiming for 14.5-16hrs of light per day (no shade! exposed to light even when eating!)
can use the masks, bright lights in stalls, etc.
describe regulating prolactin with domperidone
- dopamine D2 antagonist that increases prolactin levels which increases LH and FSH receptors
(dopamine suppresses release of prolactin, suppress dopamine and prolactin increases) - give daily until ovulation:
-15-85 days = variable response by mares
-response of mares varies by ovarian activity and temperature
-if in winter anestrus, tiny follicles not releasing much FSH to begin with = take longer to respond
-warmer temperature will respond faster; cover with blankets - very very expensive!!
-to make more cost efficient, keep under lights and indoors for 3 weeks, then begin domperidone
describe progestagens
requirements:
-late transition
- >20mm follicles
used to lengthen the diestrus period; give for approx two weeks
products: progesterone and altrenogest
summarize advancing the breeding season
- response depends on time of year and ovarian activity!!
- lighting programs are the most physiologic, consistent, and cost-effective
- must start in december with lighting, then use dopamine antagonists later in the season
describe induction of ovulation reasons and method
- synchronize ovulation with breeding
- very important with cooled or frozen semen
- minimize matings per cycle to conserve stallion power and minimize endometritis
method:
-exogenous LH: human chorionic gonadotropin (hCG)
–is a human product so expect some immune response, also after 3-4 injections may have enough antibodies built up to prevent binding to LH receptors!
-endogenous LH: GnRH agonists (deslorelin)
-give once a mare has a follicle of at least 35mm and in heat!
-once give, 80-90% of mares will ovulate within 24-48 hours (average of 36 hours)
describe induction of luteolysis indications (4)
also called “short cycling” or shortening of diestrus
indications:
1. save time after missed ovulations
2. accommodate mares to the stallion’s book
3. treat prolonged diestrus
4. induce pregnancy loss
describe method of shortening of diestrus/inducing luteolysis
use dinoprost or cloprostenol (PGF2alpha) WHEN:
-CL is present for at least 5 days
-will lyse CL and then induce estrus within 2-5 days and spontaneous ovulation within 7-10 days
often combine PGF2a with ovulation induction (GnRH or LH) if want to breed even earlier than 7-10 days
describe estrus-related complaints
- pain or sensitivity
- performance of behavioral problems
-pissy mare syndrome or mare madness - stallion-like behavior
once get these complaints, need to rule out if is estrus behavior or something else
rule outs:
-submissive behavior
-urogenital disease: pneumovagina bladder stones, urethritis
-ovarian pathology
-or truly estrus related
describe normal production of estradiol and inhibin in the follicle by granulosa and theca cells
cholesterol from blood stream reach follicle
-theca cells in response to LH convert cholesterol to androstenedione which is a percursor for testosterone
-but in the females, the androstenedione is moved to the granulosa cells where it is aromatized to estradiol in response to FSH
-granulosa cells also produce inhibin
-estradiol and inhibin released into the bloodstream to reach the hypothalamus and pituitary to exert effects
describe granulosa theca cell tumor
if composed of more granulosa cells: lots of estradiol produced, causes inhibin release and suppresses FSH = inactive follicles and ovaries
if composed of more theca cells: more testosterone produced, more stallion-like
results:
-mares may not cycle, may be in persistent heat, or may behave like stallions
diagnosis:
1. behavioral issues reported
- rectal palpation: benign, unilateral, affected side will be round, large, smooth, and NO OVULATION FOSSA, plus small, inactive contralateral ovary
- rectal ultrasound: variable
-typical: honey combed with tiny cysts around parenchyma
-can also present multi-cystic and look like mare has a bunch of follicles, but will not change in size or shape over time
-some mares: can have a large single cyst - hormone assays
–nhibin increases in 80% of tumor, testosterone increases in 48% and anti-mullerian hormone increases in abut 98% so if run all 3, gives 100% sensitivity (GCT panel includes all 3)
differential diagnoses:
-hematoma: hemorrhagic anovulatory follicle
-spring transition
-pregnancy (40-80d)
treatment:
-unilateral ovariectomy
-return to cyclicity in 2-16 months
-regain normal fertility
describe teratomas and dysgerminomas (5)
- germ cell origin
- unilateral
- hormonally inactive, so mares cycle normally
- contain hair, cartilage, teeth, bone
- teratoma is benign, dysgerminoma is malignant
describe true estrus-related problems
- muscles relax and are less supportive so minor lameness becomes more evident
- mare can become less cooperative or attentive
- sensitivity around ovaries
other clue towards just estrus-related:
-have owner keep a log of behavior; if bad all the time, not estrus, if matches estrous cycle, more likely estrus related
how do you treat estrus-related problems?
give progestagens!
suppress estrus for as long as they are administered (take about 3d from start of treatment to estrus suppression)
-not always allowed (competition rules)
describe two methods to suppress PGF2a
- oxytocin: involved in release of PGF2a
when overload endometrium with oxytocin, saturate receptors so can no longer release PGF2a
so if give oxytocin for a week, overload receptors and suppress release of PGF2a
let mare ovulate, tricker her with daily oxytocin for a week to keep CL going for about 2 months before regressing
-estrus suppression for approx 2 months
- place marbles in uterus to mimic embryo and suppress release of PGF2a
