20 Equine Theriogenology Anatomy and Understanding the Estrous Cycle

1. vulva

2. vestibulo-vaginal fold (prevents airflow into uterus when vulvar lips are pulled apart)

3. cervix

What are the 3 physical barriers to infection for the uterus in mares?

Estrus

When does the uterus have increased immunologic but decreased mechanical clearance, estrus or diestrus?

Vestibule

What is 1?

Vulva

What is 2?

Where the vestibulo-vaginal fold would be

What is 3?

Cranial vagina

What is 4?

Cervix

What is 5?

Uterine body = large in mares

What is 6?

Uterine horn, shorter and no coiling in mares

What is 7?

At "10 and 2"

Where do the ovaries normally hang by the shaft of the ileum in horses?

Intersection of vestibule and vagina

What does the vestibulovaginal fold separate?

Breaks seal of fold. May allow things we don't want into uterus. We want it to sit up and down

What happens if there is a tilt to the vestibulovaginal fold (which we normally want dorso-ventral position)?

Hymen

What is another name for the vestibulovaginal fold?

Imperforate hymen = Just need to rupture it and she should be fine

What is this and what do you do?

Ova fossa

What is the ONLY place a mare can ovulate, which you should always be able to feel in the ovary? (may have an ovarian tumor if you can't feel this indent)

Follicle

Which one is palpable in the horse, CL or Follicle?

Granulosa cells (encompasses entire follicle)

When we talk about a follicle growing, the oocyte grows within a nest of what kinds of cells?

Granulosa

Sertoli cells are equivalent to theca or granulosa cells

Theca

Leydig cells are equivalent to theca or granulosa cells

INTERNAL = granulosa

theca interna

EXTERNAL = theca externa

Going from internal to external on a follicle, what are the layers of cells in horses?

Fimbriae

What structure, when the follicle ovulates, moves the oocyte and directs it down the oviduct?

PGE2

What hormone is necessary for the uterotubular junction to open in mares, where it will not allow an oocyte/ova to pass into the uterus if it is not fertilized?

A is preferable. Upright vulva, 2/3 of vulvar opening is below brim of pelvis and there is normal apposition of the vulvar lips.

What is the difference between the vulvar confirmation of these two mares? Which is preferable?

This is the windsucker test.

In the normal image, the vestibulovaginal fold is stopping it.

What is this test? What is blocking it in the normal image?

Caslick's vulvoplasty

What is the correction for a "windsucker"?

Estrus (heat)

Urinating, ears not pinned, winking vulvar lips, tail raised, and hard to move are all signs of what part of the estrous cycle in mares?

Taylorella equigentalis

What is the causative agent of CEM, contagious equine metritis?

Clitoral sinus

Where is CEM harbored in mares?

a. pink, moist mucosa

d. cervical tone absent

c. uterine tone decreased

Select the characteristics of estrus:

a. pink, moist mucosa

b. cervix toned and puckered

c. uterine tone decreased

d. cervical tone absent

e. dull pale pink dry mucosa

f. uterine tone increased

e. dull pale pink dry mucosa

b. cervix toned and puckered

f. uterine tone increased

Select the characteristics of diestrus:

a. pink, moist mucosa

b. cervix toned and puckered

c. uterine tone decreased

d. cervical tone absent

e. dull pale pink dry mucosa

f. uterine tone increased

Melatonin

What hormone is high in anestrus in horses?

Eversion of clitoris

What is "winking" in mares?

Estrus

Is this an estrus or diestrus mare cervix?

Urine pooling

What is happening in this mare?

In the summer, when daylight is the longest

Horses are seasonally polyestrus. When are they MOST FERTILE?

1-2 days BEFORE end of estrus

When do horses ovulate in comparison to estrus?

Diestrus

CL's release progesterone which triggers the mare to go into WHAT PHASE of the estrous cycle?

Estrogen and LH

What hormones peak to cause ovulation?

Sunlight to brain --> dec. melatonin --> stimulate GnRH --> anterior pituitary to release LH and FSH --> mare cycles, follicles grow

Describe the relationship of daylight to the follicles in mares?

April

When do we start to see good regular cycles starting in mares naturally?

give 16 hours of light for 60 days (or pulse 1-2 hours of light in the middle of the night)

How do we advance the breeding season in mares who we want to breed in february instead of april?

Estrogen

note: edematous uterus is desired when trying to get mares pregnant because it indicates the mare is in heat and has a follicle ready for ovulation

An edematous uterus tells us we have estrogen or progesterone present in mares

7-14 days post partum in mares. They are LESS fertile if they are bred before day 9 post foaling.

note: it is basically the first heat the mare goes thru after birth

What is "foal heat"?

If you breed them on foal heat, they have an 11 month gestation so if you breed them during this time they will foal even earlier the next calendar year

What does it mean when I say "if the mare is bred prior to day 25 post partum you may 'advance the mare calendar'"?

Progesterone (altrenogest), estradiol, deslorelin, hCG, oxytocin, prostaglandin F2alpha

What are the names of the hormones we use in horse cycles?

Progesterone

What hormone helps to shorten the spring transition in horses and even can be used to maintain pregnancy or delay ovulation in horses?

GnRH

Deslorelin acetate or Sucromate is WHAT hormone?

38 hours

How long does it take for deslorelin to cause ovulation in horses

LH

hCG has activity like WHAT HORMONE?

36 hours (slightly shorter than deslorelin)

How long does it take for hCG to cause ovulation in horses?

hCG may cause induction of antibodies in the mare = may not work so reliably

hCG may cause ovulation faster than deslorelin. What downside comes with this?

Twin pregnancy

Deslorelin and hCG both speed up ovulation rate in horses. This increases the risk for WHAT to happen?

Oxytocin

What hormone aids in milk letdown, evacuation of uterus, and induction of parturition?

FALSE = basically just causes cramping and uncontrolled contractions. do not do for normal purposes

TRUE OR FALSE: oxytocin works better in larger doses.

Sweating, colic, inappetance

What side effects might prostaglandin F2alpha cause in horses?

Lutalyse (Dinoprost tromethamine) and Estrumate (Cloprostenol sodium)

What are the two forms of prostaglandin F2alpha which can be used in horses?

Lutalyse

Which prostaglandin F2alpha used in horses is Dinoprost tromethamine?

Estrumate or Lutalyse?

Estrumate

Which prostaglandin F2alpha used in horses is Cloprostenol sodium?

Estrumate or Lutalyse?

Estrumate (Cloprostenol sodium)

Technically, there are two forms of prostaglandin F2alpha which may be used in horses. Which one causes LESS SEVERE SIDE EFFECTS?

Prostaglandin F2alpha

Which hormone causes prolonged contraction of smooth muscle and lysis of corpus luteum?

Prostaglandin

note: estrumate is better and less severe in horses

Lutalyse (Dinoprost) and Estrumate (Cloprostenol) are WHAT?

20 mm = takes 3-5 days to become a 35 mm follicle

10 mm = takes 6-10 days to become a 35 mm follicle

How is the size of the follicle related to prostaglandin F2alphas effects in horses?

use a 20 mm and a 10 mm follicle in your example

Ecbolic = cause contraction

Are Prostaglandin F2alpha and oxytocin ecbolic or tocolytic?

Tocolytics

Which causes uterine muscle relaxation, tocolytics or ecbolics?