Lecture 20: Equine Anatomy and Estrous Cycle

How does the mares reproductive tract compare to other species?

- short and straight uterine horns

- ovary = not coiled (generally at 10 and 2 o'clock by the shaft of the ileum)

What are 5 uterine defenses?

- physical barriers to infection

- immunologic clearance

- mechanical clearance

- estrus = increased immunogenic and decrease mechanical

- diestrus = decreased immunogenic and increased mechanical

What is the mucociliary clearance mechanism?

- mucus secreting cells alternating with ciliated epithelium

- airds in clearance of foreign material and bacteria from uterus

What are the 3 physical barrier to infection in a mare's uterus?

- vulva

- vestibulo-vaginal fold

- cervix

What is the normal conformation of the vulva/perineum of a mare?

- vertical orientation

- 2/3 of vulvar opening below brim of pelvis

- normal apposition of vulvar lips

How can bad vulva/perineum conformation lead to issues with the uterine barrier?

- tilting of the vulva or less than 1/2 of the vulvar opening below the pelvic brim

- leads to contamination of reproduction with feces

How is the vestibulo-vaginal fold a uterine barrier? How can it be inpacted?

- sits up and down to create a seal for air and infectants to be cut off from entering

- no seal if in different orientation = windsucking

What is windsucking?

- lack of seal of the vestibulo-vaginal fold

- diagnose with windsuckers test

- tx: caslicks vulvoplasty

What mares need a caslicks vulvoplasty?

- obvious tilted vulva

- pneumo uterus or pneumovagina

- irregular vulvar lips

- marse w/ persistent infertility

- mares with other barrier compromise

- perineal trauma post foaling

What is palpating for a follicle and corpus luteum like in mares?

- can feel follicle well

- can't feel CL very well

What are the parts of the oviduct from the ovary down?

- ampulla = fimbria and infundibulum

- isthmus

- uterine tubal junction

How long does the embryo remains in oviduct?

- it takes 6-7 days to reach the uterus

(won't reach uterus if not fertilized)

What is CEM or contagious equine metritis?

- caused by taylorella equigenitalis

- impacts the clitoral sinuses

How do you test for CEM or contagious equine metritis?

- tested at quarantine stations

What are signs that a mare is in estrus (in heat) when presented with a male?

- urinate

- ears not back (not pinned)

- wink vulvar lips

- posture

- hard to move

- tail raised

What are signs that a mare is in diestrus (out of heat) when presented with a male?

- kick

- ears back (pinned)

- squeal

What are the physical changes of a mare during estrus?

- pink and moist mucosa

- absent cervical tone (sitting on bottom of vagina)

- edema in uterus

- decreased uterine tone

What are the physical changes of a mare during diestrus?

- dull pale pink and dry mucosa

- toned cervix = puckered

- uterus tone increased

What are the physical changes of a mare during anestrus?

- dull pale pink and dry mucosa

- absent cervical tone

- decreased uterine tone

What are the hormones like for a mare in estrus?

- high estrogen, LH, and FSH

What are the hormones like for a mare in diestrus?

- high progesterone

- peak FSH

- PGf2a peak at the end

What are the hormones like for a mare in anestrus?

- high melatonin = low GnRH, FSH and LH

What type of breeders are mares? What does this mean?

- long daylight breeders

- only 10-15% will cycle during the winter

- in the spring they have erratic cycles

- need to confirm ovulation prior to breeding

- might not get preg in the fall since can be a transitional phase

Mares are seasonal and long day breeders, how does this work?

- shorter days = melatonin is high

- spring = days get longer = less melatonin = start cycling

- most fertile during the summer

What does the vagina and cervix look like during estrus?

- vagina = pink, moist and glistening

- cervix = relaxed, melted, laying on vaginal floor

What does the vagina and cervix look like during diestrus?

- vagina = pale pink and dry

- cervix = tight, high and puckered

How long are mares in estrus and in diestrus?

- seasonally polyestrous and is ~ 21 days long

- ~ 5-7 days in estrus/heat

- 14-15 days in diestrus/out of heat

- ovulate 1-2 days before end of estrus

What time of the year is the mare most fertile?

- the SUMMER

What is the equine estrous cycle like with hormones?

- follicle grows = increase in estrogen = estrus

- follicle ovulates + oocyte into oviduct

- follicular cavity forms CL = increase progesterone = diestrus

- PG-F2a will lyse CL and bring mare back into heat if not preg

Which hormone maintains pregnancy?

- progesterone

how does the mare's LH curve differs from other species?

- LH surge occurs after ovulation, unlike cattle and small animals

- peak is broad and prolonged = last longer

How can you advance the mare breeding season?

- keep mares under lights to induce artificial photoperiod

- start at the start of december to breed in february

How long do you need to mares under lights to induce an artificial photoperiod?

- 16 hours of light for 60 days

What is a equilume?

- can provide light to a mare to mares under lights to induce artificial photoperiod

What is foal heat?

- the first estrous cycle a mare has after giving foaling

- mare has decreased fertility

- occurs 7-14 days post-partum

How can breeding in the first 30 days post-partum can advance the mare's foaling date the next year?

- it can decrease the interval between foaling

What are 5 desired effects from the manipulation of the estrous cycle?

- hasten the breeding season

- induce ovulation

- suppress estrus or sexual related behaviors

- synchronize estrous cycles

- decrease pathologic effects

Why would we use progesterone in mares?

- shorten spring transition

- maintenance of pregnancy (up to 100-120 days)

- prevent signs associated with estrus

- delay ovulation (breeding)

- synchronize estrous cycles of horses

How is progesterone and estradiol used together?

- given together for 10 days

- PGF2a given on day 10

- rests their cycle by removing progesterone and ovulates about 21 days from start of treatment

What drug so you want to give a mare that you want to ovulate around 38 hours later? What activity does it have?

- deslorelin (GnRH)

- GnRH like activity

What drug so you want to give a mare that you want to ovulate around 24-48 hours later? What activity does it have?

- human chorionic gonadotropin (hCG)

- LH like activity

(may be less reliable in older mares or multiple doses due to possible induction of antibodies)

What drug do you use to induce parturition in mares?

- oxytocine

What are uses of oxytocin in mares?

- milk let down

- induction of parturition

- evacuation of uterus

- long term suppression of estrus at high doses

What are the indications for prostaglandin F2a (lutalyse and estrumate)?

- contraction of smooth muscle

- lysis of CL at low doses

What are the side effects of prostaglandin F2a (lutalyse and estrumate)?

- sweating

- colic

- inappetance

How does the size of the follicle at the time of PGF2a administration affect the time to ovulation?

a. 20 mm follicle

b. 10 mm follicle

a. 3-5 days to become 35mm and ovulate

b. 6-10 days to become 35mm and ovulate

What are ecbolic agents, like oxytocin and PGF2a?

- cause uterine muscle contractions

- helps clean the uterus

What are tocolytic agents like terbutaline?

- causes uterine muscle to relax

- calms uterus (when trying to stop labor)

When do you use PGF2a to manipulate uterine tone?

- prior to ovulation

When do you use oxytocin to manipulate uterine tone?

- prior and post ovulation