3. therio- equine breeding mgmt and estrus manipulation

what type of ovulators are mares?

seasonal, polyestrous, spontaneous ovulators

only cycle during certain times of the year, and when in heat have multiple cycles

what is the length of diestrus in the mare?

hormonal diestrus: 14 days

behavioral diestrus: 15 days

what is the main hormone in diestrus?

progesterone (diestrus=luteal phase)

what is the importance of knowing the difference between the behavioral and hormonal phases of diestrus?

mares typically ovulate 24-48 hours before the end of behavioral estrus, meaning they are still receptive to the male/breeding a day after ovulation

ie, even though they are already in diestrus/luteal phase, they can still be behaviorally in estrus

how long is estrus in mares?

3-7 days (may be shorter later in the season)

t or f? mares will have differences in the length of estrus but most mares will have similar lengths of diestrus. 

true

what is the main hormone in estrus?

estrogen

in total, how long is a mares cycle?

18-23 days (21-22 days average)

# of FSH waves determine how long the cycle is

what is the name of the bacteria that colonizes and causes a reportable disease in the clitoral sinuses of the mare?

taylorella equigenitalis colonizes in the sinuses of the clitoris

causes the reportable disease contagious equine metritis, or CEM

what are the 3 barriers to ascending infection?

1. vulvar lips

2. vestibulo-vaginal sphincter (transition from vestibule to vagina)

3. cervix (mares have a weak muscular cervix compared to ruminants which have cartilaginous rings)

how does the cervix appear during anestrus?

pale and relaxed

how does cervical tone feel during anestrus by transrectal palpation?

cervical tone is soft, flat, and short

how does the cervix appear during estrus?

pink, moist, relaxed (to let semen in), and on floor of vagina (appears as a wilted rose)

how does cervical tone feel during estrus by transrectal palpation?

cervical tone is slightly more toned than in anestrus

how does the cervix appear during diestrus?

pale, dry, tight (to keep baby in, and keep bad things out), projects into vagina (appears as a rose bud)

how does cervical tone feel during diestrus by transrectal palpation?

toned, short 'hot dog'

what is the cervical tone of the cervix during pregnancy?

toned, long 'hot dog'

where does fertilization of sperm occur?

in the oviduct

can unfertilized ova enter the uterus of mares?

no, only fertilized ova (embryo) enter the uterus 5-6 days post-ovulation

this is different in cows- cows can release fertilized and unfertilized oocytes into the uterus

are mares ovaries able to move as freely as bovine ovaries?

no

how else do equine ovaries differ from bovine ovaries?

the equine ovary is reversed, where the medulla is on the outside and the cortex is on the inside of the ovary

horses also have an ovulation fossa, where ovulation occurs

can you palpate CLs in mares? cows?

no, the CLs in mares are not palpable

CLs in cows are palpable

what is the ovulation depression?

after mares ovulate thru the ovulation fossa, the follicle depresses for a few hours and is referred to as the ovulation depression

this depression then refills with blood to become the corpus hemorrhagicum (which may be mistaken for a follicle)

how does the size of the mares ovaries vary?

size of ovaries varies depending upon season and stage of cycle:

-during seasonal transitions, ovaries can be large with numerous persistent follicles

-during anestrus, ovaries are small with an absence of follicles

what is the size of ovulatory follicles in mares? how does this differ from other species?

35-55mm in diameter

markedly larger than other species- ovulatory follicles in cows usually no bigger than 17mm

what are possible reasons for abnormally small and inactive ovaries in mares?

-R/O seasonal influences

-history of anabolic steroid administration

-chromosomal abnormalities

what are possible reasons for abnormally large ovaries in mares?

R/O seasonal influences (AHF), neoplasia (granulosa cell tumor most common)

-mares do not develop cystic ovarian disease

-epithelial inclusion (fossa) cysts can invade the ovarian stroma causing infertility in older mares

what occurs as the follicle diameter increases?

as diameter increases, it migrates towards the ovulation fossa

this is evident by irregularly shaped, scalloped, or flattened follicles

when does shape change of the follicle occur?

shape change occurs within 24 hours of ovulation

usually turns into a tear-drop shape

is there uterine edema in the mare during diestrus?

no edema during diestrus

on U/S, the uterus appears homogenous, and the lumen and endometrial folds are not visible

is there uterine edema in the mare during estrus?

yes, under the influence of estrogen, there is increased blood flow/edema to the uterus

on U/S, the uterus appear heterogenous, and endometrial folds are seen (look like a wagon wheel)

how is uterine edema sometimes useful to predict ovulation?

using edema and its change over time may be used to predict ovulation, as uterine softening occurs with estrus edema

edema peaks 1-3 days before ovulation, and is gone by 1-5 days after ovulation

what is a grade 1 rectal tear?

mild tear in mucosa, +/- submucosa

what is a grade 2 rectal tear?

muscularis layer only

fecal impactions may cause, are rare

what are grade 3 rectal tears?

3a: all layers but serosa (doesnt disect)

3b: some disect

what is a grade 4 rectal tear? what is the prognosis?

full thickness tear- life ending

why is light needed to stimulate early season breeding in mares?

mares are long-day breeders

how much light is needed to stimulate early season breeding in mares?

light must be bright enough to read newsprint at arms length away anywhere in the stall

duration of 16 hours of light needed- increase day length after sunset for a total of 16 hours

when should you begin to supplement light to stimulate early season breeding?

begin early to mid december

mares typically ovulate 6-10 weeks after starting

what does prolactin stimulate release of in the horse? how does this differ from dogs?

in horses, prolactin stimulates GnRH release, and is lower in the winter than summer

the dog is opposite (PRL inhibits release of GnRH)

what inhibits prolactin release?

dopamine

how much do follicles grow each day in mares?

follicles grow 3-5mm a day

reach max. size 1-3 days prior to ovulation and plateau (receptivity continues for 24-48 hours post ovulation)

when does the LH peak occur in mares?

1-2 days after ovulation

when do FSH peaks occur in mares?

FSH peaks 1-2x during diestrus in 1-2 follicular waves

why don't mares ovulate during diestrus when there is a second follicular wave?

progesterone from the CL inhibits LH, and estrogen down-regulates FSH

how does the use of progesterone control mares cycles?

progestogens lengthen the luteal phase which in turn suppress estrus/ovulation, and can help in pregnancy maintenance

ie, progesterone is given to make the mare think she is pregnant so ovulation doesnt occur

how does the use of hCG control mares cycles?

hCG has LH-like activity: maintains CL so the uterus doesnt release prostaglandins

only effective on 35mm or bigger growing follicles

how are dopamine antagonists used to control mares cycles?

used to stimulate early onset of estrus during non-breeding seasons

what are the human exposure risks of progesterone administration?

if absorbed into the skin, can decrease the sperm quality in males, and messes with the cycles of females

how are prostaglandins (PGF2a) used to control mares cycles?

PGF2a is used to induce estrus by terminating the luteal phase

uses:

-used in cases of prolonged diestrus

-pregnancy termination

-ecbolic (induces uterine contractions)

when is the CL responsive to PGF2a?

the CL is responsive 5-13 days (usually 5-7 days) post ovulation

have to wait for CL to be completely mature before giving prostaglandins

what is the interval from treatment with PGF2a to ovulation?

ovulation will occur in 2-15 days

when should you give mares in diestrus prostaglandins if trying to breed?

depending on follicle size (if bigger, ovulates faster)

if given 4 days after ovulation, will return to estrus in 2-4 days, and will ovulate 8-12 days after treatment

these parameters can be used to determine when to breed/ordering semen for AI

what are the possible adverse affects of prostaglandin exposures in people?

if pregnant, may cause abortion

in those with bronchial or other respiratory problems, may cause bronchiospasms

when should a post-breeding exam be performed? what is the importance?

within 12 hours after breeding

confirms ovulation has occurred and determines if post-mating induced endometritis is present

how is insemination performed with cooled semen?

semen is deposited within the uterine body

how should insemination with poor quality semen be performed?

inseminate with entire dose as close to ovulation

how should 'susceptible' mares be inseminated?

inseminate with the minimum dose once within 24 hours prior to ovulation

does fresh, chilled, or frozen semen have the best quality?

fresh > chilled > frozen

which mares are selected for insemination with frozen semen?

select mares with history of good fertility

how are mares being bred with frozen semen managed?

-examine mares every 24-48hrs until close to ovulation, then every 4-6 hours

-inseminate within 6-12hrs prior to ovulation or within 2-4hrs after ovulation

-deep horn insemination (deposit semen near uterotubal junction ipsilateral to ovulation)

what is the breeding criteria for postpartum, 'foal heat' mares?

1. normal foaling (no dystocia, retained placenta, neonatal death)

2. normal uterine involution (palpably reduced in size)

3. no cervical tears or excessive bruising

4. only if ovulation occurs over 10 days post foaling

why is it important to breed postpartum mares only if ovulation occurs 10 or more days post foaling?

because 15 days is needed for complete endometrial repair