10. Estrous Cycle and Manipulation

What is the character of uterus and cervix during estrus? What do you see on ultrasound?

• Cervix and uterus relaxed

• Uterine Edema on u/s

What is the character of uterus and cervix during diestrus? What do you see on ultrasound?

• Uterus "toned"

• No edema on u/s

• Cervix tightly closed

How many follicles does the mare ovulate per cycle?

1-2 follicles (think of these as what may potentially become a foal)

How many mm does the follicle grow each day and what does it depend on?

3-5 mm/day depends on the mare and season

At what size does the follicle ovulate?

40-50 mm

What are the FOUR reasons that the owner may want to manipulate the cycle of the mare?

1. induced ovulation for the mare to be bred at a precise time

2. hasten return to estrus (short cycle)

3. synchronize estrous cycle in group of mares

4. hasten onset of breeding cycle (decrease transition period)

Which transitional period are we usually trying to shorten?

early spring

What is happening durning the transition period?

variable follicular growth due to increasing levels of FSH and LH

T/F There is ovulation occurring during the transitional period

False, none is happening

What is the best way to manipulate the transition period?

increase the photoperiod

What is the cheapest, most effective and easiest way to manipulate the photoperiod? Why do you do this?

artificial lighting because mare's are long day breeders so the light tricks them to suppress melatonin from the pineal gland which leads to the start of the HPG axis

What is the least amount of days that the mare needs to be exposed to for the artificial lighting to be effective?

60 days

What is the total number of light that you would want to expose your mare to per day to manipulate the photo period?

14-16 hours (turn on before dark (4pm) and off at 11pm)

What drugs could you give to a mare that does no respond as well to the light for additional help to hasten the onset of the season?

Sulpiride or Domperidone

What hormone does Sulpiride or Domperidone suppress? What does this lead to an increase of?

Dopamine antagonists which leads to an ↑ Prolactin

What does a ↑ in Prolactin do physiologically?

increases the number of FSH and LH receptors on the ovary which helps to hasten the onset of the season

What is a con to using Sulpiride or Domperidone?

it is expensive and labor intensive (you have to give these drugs q 24 hours for 3 weeks or until ovulation)

What hormones can you give to hasten the onset of the season? (2)

Progesterone OR Progesterone + Estradiol 17-ß

What is the goal when you give Progesterone OR Progesterone + Estradiol 17-ß?

to stimulate an artificial luteal phase in order to increase stores of LH

T/F If there is a CL that is seen on the ovary, the mare is classified as cyclic because they have ovulated

True

In order to induce ovulation, what size does the follicles need to be?

35-45 mm

T/F You will always see ovaries on the follicles even if there is no CL

True (due to the follicular waves that happen, and FSH is not controlled by P4)

Which way will the follicle point on ultrasound?

toward the ovulation fossa

What THREE things need to be present in the mare to breed her?

- uterine edema

- dominat follicle

- soft cervix

What drug is used to induce ovulation that acts like GnRH?

deslorelin

What drug is used to induce ovulation that acts like LH?

hCG

Farmer Dan has a prime Herford cow, Suzie, that kinda sucks at keeping up with her counterparts. All of them have ovulated, except Suzie, her follicle measures 32 mm. You give her a shot of deslorelin, when will you expect her to ovulate?

40-41 hours later (note to give desolrelin the follicle must be at least 30 mm in size)

T/F Ovuplant is a subdermal implant that is used commonly in the US and you must remove it after ovulation

False, it is no long available in the US

What drug is used the majority of the time and acts like LH?

hCG

If you give a shot of hCG (chorulon), when would you expect the mare to ovulate?

36-48 hours later

What is a major concern with giving hCG?

antibody formation ( this happens because it is a human drug that is given to a horse so the horse's body sees it as foreign)

T/F hCG is given IV so that there is a decreased antibody production

True

What is the class of drugs that are given if you want to short cycle your mare?

Prostaglandins

What is the MOA fo Prostaglandins?

Luteolytic: (kills the CL)

How old must the CL be to be classified as mature, therefore the PGF2a will not work? (she said this will prob be a test question)

6 days

What does administration of PGF2a hasten?

Hasten return to estrus

T/F The return to estrus is variable when PGF2a is given due to variable follicle size but it is usually 2-4 days

True

What are the TWO drugs that you can give for short cycling?

- Dinoprost tromethamine (Lutalyse)

-Cloprostenol (Estrumate®)

What effect does PGF2a have?

ecbolic

What are the side effects that are seen with administration of PGF2a?

- sweating

- smooth muscle contractions (colic and respiratory issues)

What group of people need to be cautious when handling prostiglandins?

- pregnant women

- asthma

What needs to be given for estrous synchronization twice 14 days apart?

Prostaglandins

What are TWO instances that the mare will NOT ovulate when you give her a shot of PG?

- if she has already ovulated and is in heat

- if the CL is not 6 days old

What is given for 10-14 days in a row that prolongs the luteal phase and holds the mare in diestrus?

progestins (regu-mate)

On the last day of treatment, what do you give to lyse the CL at the same time? What happens for 4-7 days after the shot is given?

- PGF2a

- starts estrus

What is expected to happen 5-12 days after PGF2a is given?

ovulation

Why are CIDRs not typically used in mares?

it causes vaginitis (which owners are very not happen about)

You're a young inspiring equine veterinarian. You are set out to your first farm during breeding season and you are trying to synchronize 14 mares so that they can be bred at the same time, relatively. Run me, the senior vet, through the typical treatment plan using progestins.

- give altrenogest (regumate) orally q24 hours for 10 days

- on day 10 give PGF2a

- all mares SHOULD ovulate within the next week (5-12 days post Tx)

Why is the range at which they are suppose to ovulate after being given PGF2a so large (5-12 days)?

this is due to the follicles all being at different stages of their growth because progesterone does not control FSH (this means that they are all going through the follicular growth waves while progesterone is rising until there is a dominate follicle that is ready to ovulate)

What hormone needs to be present to inhibit the release of FSH?

estrogen

When you are trying to synchronize estrus for embryo transfer, what is the best protocol to use because it inhibits FSH release so there is a more uniform inhibition which helps due to the follicles being similar in size so they approach ovulation at a uniform rate?

Progesterone + Estradiol 17- β

What hormone lyses the CL?

PGF2a

What hormone induces ovulation?

LH

T/F Estrumate has less side effects than leutolyse

True