FINAL EXAM: Hormonal Manipulation of Estrus Cycle

Question 1

Use of PGF2a (regress CL)

Answer 1

1. synchronize
2. short cycle/miss ovulation
3. post-partum mares
4. PGF2a- persistent CL

Question 2

Post partum mares cycle:

Answer 2

• 1st post partum estrus ~7-11 days
• 1st ovulation ~9-14 days post part
• 2nd post-partum estrus ~26-32 days post-partum
• 2nd ovulation 30=35 day pp

Question 3

Breeding on Foal heat

Answer 3

• earlier foal next year

but: lower pregnancy rates, lower live foal rate(increase embryonic loss)

Question 4

If ovulation occurs after day 15 and mare is normal in all regards…

Answer 4

It is okay to breed early on foal heat

Question 5

Mare foals on May 1st- ovulates on day 9

Answer 5

• probably don’t breed her on 1st heat cycle
• let her go through her heat and complete estrus
• then use PGF2a to short cycle
• you’ll get in between 1st and 2nd
• good foal rate and live rate
• good way to get an “earlier foal”

Question 6

PGF2a- Persistant CL

Answer 6

• cl does not regress normally
• as a result, she doesn’t return to its own estrus
• give PGF2a to regress CL
• Regresses ~80% of persistent CL

Question 7

Ovulatory agents

Answer 7

1. HCG- human chorionic gonadotropin
2. Deslurein acetate (newer)
   (1&2 induce ovulation when large developed follicle is present

Question 8

Why would you want to ovulate within 48 hours?

Answer 8

• ensure you still have live semen
• give to her before you inseminate
• then she’ll ovulate while you have live semen
• frozen semen is much shorter so admits the drug earlier on
• drugs are very effective

Question 9

Advantages of ovulatory agents

Answer 9

Timing of insemination and ovulation is improved
-reduces labor and cost if you don’t have to order semen a second time or inseminate 2nd time
Pregnancy rates are similar to normal (can be even better)

Question 10

Disadvantages of ovulatory agents

Answer 10

• HCG: some mares will become resistant
• increase multiple ovulations (good in ET)
• must know about follicular development

Question 11

Progesterone/Progestins:

Answer 11

1. delaying foal heat until day ~15 post part sometimes used with estradiol
   - give for 8-15 days, then give PGF2a = 1st ovulation ~day 20

Question 12

Advantages to progesterone

Answer 12

Gives uterus more time to recover

Question 13

Disadvantages to progesterone

Answer 13

Daily administration of p4

*another way to delay foal heat and shorten cycle like PGF2a

Question 14

Estrus synchronization

Answer 14

-administration (often with estradiol) to cycling mares for 10-14 days, then PGF2a

Question 15

Advantages of estrus sync.

Answer 15

Mares reach estrus at same time

Question 16

Disadvantages of estrus sync.

Answer 16

Daily administration

Question 17

Transitional Mares

Answer 17

-administer (often with E2) to late transition mares for 10-14 days; then PGf2a

Question 18

Suppress estrus in performance mares

Answer 18

• keep out of heat

- not always focused/difficult to manage when in heat so give P4