Manipulating the Estrous Cycle

Question 1

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

Answer 1

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

Question 2

Ovulatory agents

Answer 2

induce ovulation

Question 3

What must you have in order to use ovulatory agents?

Answer 3

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

Question 4

What are some commercially available ovulatory agents?

Answer 4

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

Question 5

Are ovulatory agents effective?

Answer 5

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

Question 6

Advantages of giving ovulatory agents before breeding:

Answer 6

shorter interval for fertilization once bred

Question 7

Disadvantages of giving ovulatory agents before breeding:

Answer 7

could ovulate too early

Question 8

Advantages of using ovulatory agents:

Answer 8

-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)

Question 9

Disadvantages of using ovulatory agents:

Answer 9

-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)

Question 10

Luteolytic agents

Answer 10

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

Question 11

What is a common type of luteolytic agent?

Answer 11

synthetic prostaglandins

Question 12

Commercial products of luteolytic agents:

Answer 12

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

Question 13

Primary purpose of luteolytic agents:

Answer 13

lysis of CL to shorten diestrus

Question 14

When should luteolytic agents be administered?

Answer 14

about 5-6 days post ovulation

Question 15

What must be present for luteolytic agents to work

Answer 15

the CL

Question 16

When will estrus begin post administration of luteolytic agents?

Answer 16

about 3-4 days post administration

Question 17

When will ovulation occur post administration of luteolytic agents?

Answer 17

about 6-10 days post administration

Question 18

Luteolytic agents can shorten time between ovulations by:

Answer 18

about 6 days

Question 19

Short cycling

Answer 19

shortening the time between cycles (using luteolytic agents)

Question 20

When to short cycle a mare:

Answer 20

-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

Question 21

Why synchronize mares?

Answer 21

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

Question 22

Why not breed on foal heat?

Answer 22

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

Question 23

Steps to administering luteolytic agents in the post-partum mare

Answer 23

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

Question 24

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

Answer 24

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

Question 25

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

Answer 25

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

Question 26

Luteolytic agents can also be used for:

Answer 26

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

Question 27

Progesterones can be used to manipulate estrous cycles by:

Answer 27

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

Question 28

Commercially available progesterone products:

Answer 28

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

Question 29

Uses of progesterone in the non-pregnant mare:

Answer 29

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

Question 30

Progesterone can be used to delay foal heat by:

Answer 30

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

Question 31

What are some cautions/concerns with delaying foal heat?

Answer 31

-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

Question 32

Luteolytic agents are _____ and _____ _____ than progesterones

Answer 32

easier and less risk

Question 33

Using progesterones to synchronize mares:

Answer 33

-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

Question 34

What is the advantage of using progesterones to synchronize mares?

Answer 34

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

Question 35

Managing the transition phase with progesterones:

Answer 35

-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)

Question 36

Using progesterones for keeping mares out of heat:

Answer 36

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

Question 37

Using progesterones in the pregnant mare:

Answer 37

-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

Question 38

Management tools for reproductive efficiency in mares:

Answer 38

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

Question 39

What is the goal of managing reproductive efficiency?

Answer 39

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