Manipulating the Estrous Cycle Flashcards
What must you know in order to manipulate the estrous cycle?
knowledge of the function and timing of the major regulatory hormones and ovarian structures
Ovulatory agents
induce ovulation
What must you have in order to use ovulatory agents?
a pre-ovulatory follicle (30-35 mm +)
What are some commercially available ovulatory agents?
-Human chorionic gonadotropin (hCG) - acts as LH
-Deslorelin (sucramate) - GnRH analog stimualtes release of LH (acts on the anterior pituitary)
Are ovulatory agents effective?
yes, essentially they are effective in knowing once given, the mare will ovulate in 48 hours
Advantages of giving ovulatory agents before breeding:
shorter interval for fertilization once bred
Disadvantages of giving ovulatory agents before breeding:
could ovulate too early
Advantages of using ovulatory agents:
-decrease incidence of 2 covers/cycle
-ovulation timed to sperm availability (“appointment breeding”)
-synchronize mares (ovulate at the same time-important for embryo transfer donors and recipients)
Disadvantages of using ovulatory agents:
-some risk of it not working
-cost (hCG costs less than Des-)
-increase twinning (double ovulation)
-hCG may lose effectiveness with time (mares can make antibodies and have an anaphylactic reaction)
Luteolytic agents
a normal cycle occurs, they lyse the CL by PGF2alpha from a non-pregnant uterus
-mimic action of natural PGF2alpha
What is a common type of luteolytic agent?
synthetic prostaglandins
Commercial products of luteolytic agents:
-lutalyse - some side effects (sweating, uterine contractions, acting collicy, etc.)
-estrumate - milder side effects
Primary purpose of luteolytic agents:
lysis of CL to shorten diestrus
When should luteolytic agents be administered?
about 5-6 days post ovulation
What must be present for luteolytic agents to work
the CL
When will estrus begin post administration of luteolytic agents?
about 3-4 days post administration
When will ovulation occur post administration of luteolytic agents?
about 6-10 days post administration
Luteolytic agents can shorten time between ovulations by:
about 6 days
Short cycling
shortening the time between cycles (using luteolytic agents)
When to short cycle a mare:
-missed ovulation/breeding (semen didn’t arrive, mare ovulated earlier than expected, mare has a + uterine culture that has to be treated)
-synchronize mares
-after foal heat
Why synchronize mares?
- convenience and economics
-several mares in heat at the same time (vet sees all the mares on the same day)
-transport all mares to stallion on same day
-mares foal at similar times - embryo transfer
-donor and recipient must be in the same reproductive status allows heat to begin on similar day and ovulate about the same time
Why not breed on foal heat?
-may have reduced pregnancy rates
-may have increased early pregnancy loss
Steps to administering luteolytic agents in the post-partum mare
- monitor for post-partum heat but don’t breed
- administer PGF2alpha about 5 days after foal-heat ovulation
- expect next ovulation 6-10 days later
Would you use luteolytic agents in mares that were bred and did not conceive?
not usually because you first know if a mare is not pregnant about 14 days after ovulation and by then the mare will already be moving into estrus
When could you use it on mares that were bred and did not conceive?
for embryo transfer
-because you collect the embryo on day 7 so you would know by day 7
-if you short cycle you shorten her cycle by a week
Luteolytic agents can also be used for:
removing a persistent CL in a non-pregnant mare so the mare can resume normal cycles
Progesterones can be used to manipulate estrous cycles by:
-suppressing estrus
-closing the cervix
-supporting the uterus during pregnancy
Commercially available progesterone products:
-injectable progesterone (can be long-lasting)
-altrenogest (Regumate) - given orally (some injectable products)
Uses of progesterone in the non-pregnant mare:
-delaying foal heat
-synchronizing mares
-managing the transition phase
-keep mare out of estrus
Progesterone can be used to delay foal heat by:
administering altrenogest for 8-15 days post partum followed by PGF2alpha
-ovulation about 15-22 days post partum
What are some cautions/concerns with delaying foal heat?
-it is not for mares with poor repro health
-it closes the cervix and can trap post-foaling fluids and stuff up there
-altrenogest exposure to humans is not desirable
Luteolytic agents are _____ and _____ _____ than progesterones
easier and less risk
Using progesterones to synchronize mares:
-often used with estrogen (give combination for 10 days than give PGF2alpha)
-mares should enter estrus at similar times
-then use ovulatory agent to synchronize
What is the advantage of using progesterones to synchronize mares?
-more effective than PGF2alpha alone
-mares do not need to have a mature CL
Managing the transition phase with progesterones:
-may shorten the transition phase or may just synchronize mares
-mares must be close to the end of transition
-administer 10-15 days followed by PGF2alpha (can plan ahead to have mares ready for breeding in Feb if used with lighting)
Using progesterones for keeping mares out of heat:
-performance mares have more consistent temperament
-not in heat at events when stallion are present
-minimize any discomfort associated with large follicles
Using progesterones in the pregnant mare:
-mares with low endogenous progesterone can use for pregestational effects on uterus and cervix
-after twin reduction to support the remaining embryo
-recipient mares post-transfer to make the uterus as friendly as possible
-in mares with at-risk pregnancies
Management tools for reproductive efficiency in mares:
-advancing the breeding season
-evaluating reproductive health
-monitoring the estrous cycle
-manipulating the estrous cycle
What is the goal of managing reproductive efficiency?
to maximize live foal rates, pregnancy rates, minimize breedings/pregnancy, and produce early foals
