Equine Reproduction Part 2 Flashcards
where do the 2 sets of hormones that primarily control the events that occur during the estrous cycle come from?
- from the anterior pituitary gland
- from the ovary
what 2 estrous cycle/repro hormones does the anterior pituitary gland produce?
- follicle stimulating hormone (FSH)
- luteinizing hormone (LH)
what does FSH stimulate in the ovary (2)
- follicular recruitment
- follicular growth
when does LH reach its highest levels in the estrous cycle?
toward the end of estrus
what is LH responsible for in the mare? (4)
- follicular maturation
- estrogen production
- ovulation (due to a surge in LH)
- luteinization (CL development)
what stimulates release of FSH and LH?
GnRH released from the hypothalamus
what are the 2 hormones in mares that are released from the ovaries? what kind of hormones are these?
estrogen and progesterone, steroid hormones
when and where is estrogen released from in the mare?
from the growing follicle in the ovary
what are the 3 general effects of estrogen in mares?
- initiation of standing heat/estrus behavior
- dilation of the cervix/production of clear mucus for the sperm to enter the tract
- changes in the environment of the oviducts in preparation for ovum and sperm transport
describe the changes in the environment of the oviducts in preparation for ovum and sperm transport as initiated by estrogen (2) and give general reason for these changes
- elevated secretory activity
- enhanced uterine motility
to make it easier for sperm to reach ovum
what produces progesterone?
the mature CL
what does progesterone do? (2)
- causes cervix to tighten to keep foreign material out
- readies the uterus for pregnancy
what are prostaglandins? (2)
- naturally occurring compounds
- synthesized in most body tissue
what is another name for C-20 fatty acid?
PFG2a (alpha)
when is PGF2a released and by what?
released by the endometrium toward the end of diestrus (between day 13-16 after ovulation)
what is the endometrium?
uterine lining
what does PGF2a cause? (2)
- regression of the CL to remove influence of progesterone
- stimulates smooth muscle contractions
what can be caused by the smooth muscle contractions stimulated by PGF2a if a mare is pregnant when it is given to her?
abortion
what are the 2 phases of the estrous cycle?
- follicular phase
- luteal phase
when does the follicular phase begin?
when the anterior pituitary gland produces FSH to stimulate development of follicles
what is the beginning of estrus associated with, hormonally and why?
elevaated blood concentrations of estrogen secreted from developing follicles
what is the exception to the elevated blood concentration of estrogen that often signals the beginning of estrus?
when a mare is in her transitional period, estrogen levels in blood may not rise as the first few heats are irregular and erratic
what happens hormonally shortly after the increase in estrogen concentration at the beginning of estrus?
the concentration of LH also begins to rise; rise in estrogen levels results in positive effect on LH release from anterior pituitary
what causes ovulation hormonally?
LH surge
when does the luteal phase begin?
following ovulation
what happens hormonally after ovulation/during luteal phase?
cells in CL begin to produce progesterone
how long can a rise in progesterone levels be detected?
approximately 24 hours after ovulation
what happens to cause a mare to go out of heat, hormonally? what happens next?
progesterone reaches sufficient level; but progesterone continues to rise from there as CL becomes more mature
how long does it take a CL to become fully functional?
about 5 days
what can be administered to cause CL regression and why would this be done?
can administer lutealyse (a synthetic PGF2a) to cause CL regression; this shortens the cycle so the next heat cycle occurs sooner, which is good because due to the seasonal polyestrous nature of horses, you only have so many chances to breed them and can increase that number of chances to breed using lutealyse
what must you be SURE of before administering lutealyse to a mare you are trying to breed? why?
make sure she is not already bred!! will abort!!
what happens if a mare does not become pregnant during the luteal phase/what comes next? (5)
- PGF2a is released from the uterus
- this causes CL regression
- progesterone levels reduce
- this allows mare to return to estrus as, as the same time that PGF2a is being released (d13-16 after ovulation), the anterior pituitary will also release FSH, stimulating follicular growth and the return to the follicular phase
- subsequently, estrogen concentrations will rise and the cyle repeats
what happens if a mare does become pregnant?
- effects of PGF2a are blocked
- CL is maintained 180-220 days of pregnany
- supplementary follicles grow and develop accessory CL’s that are maintained for the same period of time as the main CL
what is the main source of progesterone during pregnancy? what are supplementary sources?
main: placenta
supplementary: CL and accessory CLs
what is a unique feature of the equine placenta?
endometrial cups
what are endometrial cups?
irregular outgrowths on the luminal surface of the gravid (pregnant) horn
describe the life cycle of endometrial cups
develop by approx day 35
max size around day 70
completely sloughed around day 130
what do endometrial cups do?
secrete eCG (equine chorionic gonadotropin)
what are the functions of enquie chorionic gonatotropin hormone (eCG) as released by endometrial cups? (2)
- assist in formation of supplementary CLs to provide more progesterone
- stimulus for maintenance of primary CL between day 35-120
AKA: another failsafe to help mare maintain her pregnancy
when does the placenta become the primary source of progesterone?
around day 180 of pregnancy
describe maternal recognition of pregnancy (3)
- presence of conceptus causes prevention of luteolysis
- endometrial production of PGF2a significantly reduced
- early embryo expresses enzymes for synthesis of prostaglandins E and F
in the early days of pregnancy (days 12,13,and 14, or 14-16 days after ovulation) what is the conceptus doing? why?
migrating from one horn to the other within the uterus; likely to distribute pregnancy recognition factor to endometrial cells
when does the conceptus fixate/attach to the endometrium? when is it well established where it is?
attaches on day 16 of pregnancy; is well established by 40-45 days
when is a good/common time for a mare to lose a baby
before it is established/fixed to the endometrium, or before 40-45 days
what is a failsaife in the endometrial cells of the mare just in case PGF2a production doesn’t stop/decrease thanks to the conceptus distributing prgnancy recognition factor?
the factor reduces the receptors for PGF2a in endometrial cells, so even if it is still produced, its effects are decreased
what must happen before lutealyse is given in order for it to work?
CL must be fully functional
describe what you would do in a breeding program where you just missed a mare’s estrus
wait until CL fully functional, then administer lutealyse to cause CL regression and initiate next cycle; if have semen but follicles not big enough on palpation, give sucramate to stimulate ovulation, and then breed; but if miss even this ovulation, go ahead and breed ASAP because might still catch an ovum with the semen since we have it
what is sucramate (2)
- also called deslorelin
- stimulates ovulation within 24-48 hours of administration
what can you do if a mare is having twins to make her not have twins? (give both for twins in each horn and twins both in one horn)
one twin each horn: pinch on horn to terminate one of them
both twins in one horn: can still pinch to terminate but must be very careful to ensure you only damage one twin
