Manipulating the Estrous Cycle Flashcards

1
Q

What must you know in order to manipulate the estrous cycle?

A

knowledge of the function and timing of the major regulatory hormones and ovarian structures

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2
Q

Ovulatory agents

A

induce ovulation

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3
Q

What must you have in order to use ovulatory agents?

A

a pre-ovulatory follicle (30-35 mm +)

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4
Q

What are some commercially available ovulatory agents?

A

-Human chorionic gonadotropin (hCG) - acts as LH
-Deslorelin (sucramate) - GnRH analog stimualtes release of LH (acts on the anterior pituitary)

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5
Q

Are ovulatory agents effective?

A

yes, essentially they are effective in knowing once given, the mare will ovulate in 48 hours

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6
Q

Advantages of giving ovulatory agents before breeding:

A

shorter interval for fertilization once bred

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7
Q

Disadvantages of giving ovulatory agents before breeding:

A

could ovulate too early

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8
Q

Advantages of using ovulatory agents:

A

-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)

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9
Q

Disadvantages of using ovulatory agents:

A

-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)

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10
Q

Luteolytic agents

A

a normal cycle occurs, they lyse the CL by PGF2alpha from a non-pregnant uterus
-mimic action of natural PGF2alpha

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11
Q

What is a common type of luteolytic agent?

A

synthetic prostaglandins

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12
Q

Commercial products of luteolytic agents:

A

-lutalyse - some side effects (sweating, uterine contractions, acting collicy, etc.)
-estrumate - milder side effects

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13
Q

Primary purpose of luteolytic agents:

A

lysis of CL to shorten diestrus

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14
Q

When should luteolytic agents be administered?

A

about 5-6 days post ovulation

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15
Q

What must be present for luteolytic agents to work

A

the CL

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16
Q

When will estrus begin post administration of luteolytic agents?

A

about 3-4 days post administration

17
Q

When will ovulation occur post administration of luteolytic agents?

A

about 6-10 days post administration

18
Q

Luteolytic agents can shorten time between ovulations by:

A

about 6 days

19
Q

Short cycling

A

shortening the time between cycles (using luteolytic agents)

20
Q

When to short cycle a mare:

A

-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

21
Q

Why synchronize mares?

A
  1. 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
  2. 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
22
Q

Why not breed on foal heat?

A

-may have reduced pregnancy rates
-may have increased early pregnancy loss

23
Q

Steps to administering luteolytic agents in the post-partum mare

A
  1. monitor for post-partum heat but don’t breed
  2. administer PGF2alpha about 5 days after foal-heat ovulation
  3. expect next ovulation 6-10 days later
24
Q

Would you use luteolytic agents in mares that were bred and did not conceive?

A

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

25
Q

When could you use it on mares that were bred and did not conceive?

A

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

26
Q

Luteolytic agents can also be used for:

A

removing a persistent CL in a non-pregnant mare so the mare can resume normal cycles

27
Q

Progesterones can be used to manipulate estrous cycles by:

A

-suppressing estrus
-closing the cervix
-supporting the uterus during pregnancy

28
Q

Commercially available progesterone products:

A

-injectable progesterone (can be long-lasting)
-altrenogest (Regumate) - given orally (some injectable products)

29
Q

Uses of progesterone in the non-pregnant mare:

A

-delaying foal heat
-synchronizing mares
-managing the transition phase
-keep mare out of estrus

30
Q

Progesterone can be used to delay foal heat by:

A

administering altrenogest for 8-15 days post partum followed by PGF2alpha
-ovulation about 15-22 days post partum

31
Q

What are some cautions/concerns with delaying foal heat?

A

-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

32
Q

Luteolytic agents are _____ and _____ _____ than progesterones

A

easier and less risk

33
Q

Using progesterones to synchronize mares:

A

-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

34
Q

What is the advantage of using progesterones to synchronize mares?

A

-more effective than PGF2alpha alone
-mares do not need to have a mature CL

35
Q

Managing the transition phase with progesterones:

A

-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)

36
Q

Using progesterones for keeping mares out of heat:

A

-performance mares have more consistent temperament
-not in heat at events when stallion are present
-minimize any discomfort associated with large follicles

37
Q

Using progesterones in the pregnant mare:

A

-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

38
Q

Management tools for reproductive efficiency in mares:

A

-advancing the breeding season
-evaluating reproductive health
-monitoring the estrous cycle
-manipulating the estrous cycle

39
Q

What is the goal of managing reproductive efficiency?

A

to maximize live foal rates, pregnancy rates, minimize breedings/pregnancy, and produce early foals