Section 3: Equine Flashcards
what forms the first seal that protects the female reproductive tract?
vulvar seal
what is normal conformation of the vulva and perineum important for?
preventing contamination of the anterior genital tract with air and bacteria
where does the clitoris lie?
within clitoral fossa at the ventral aspect of the vulvar commissure
what are the three main physical barriers to protect the uterus?
vulva
vestibule
cervix
what forms a vestibulovaginal seal?
transverse fold and vestibular constrictor muscles
what seal should prevent air and contaminants from entering the vagina even if the vulvar lips are parted?
vestibulovaginal seal
is the vagina sterile?
no
small numbers of commensal bacteria are found
what type of folds does the mare cervix have?
longitudinal mucosal folds
does the mare’s cervix have obstructing fibrous rings like ruminants and pigs?
no
how does the mare’s cervix change during the estrous cycle?
estrus: soft and easily dilated
diestrus and pregnancy: firm and tightly closed, projecting into cranial vagina
what suspends the uterus within the abdomen?
two large broad ligaments
is the endometrium glandular?
highly glandular
what type of folds does the endometrium have?
prominent longitudinal folds
mare ovaries are _____________ than ovaries of the other farm species
larger
how is the mare ovary unique?
arrangement of the cortex and medulla are reversed compared to other animals
where does the cortex of the mare ovary reach the surface?
ovulation fossa only
does the corpus luteum protrude from the surface of the ovary in a mare?
no
the mare’s udder consists of two mammary glands, with ________________ streak canals per teat
two, sometimes three
what part of the oviduct attaches to the ovary?
infundibulum with fimbriae
when does puberty occur in the filly?
12-24 months of age
when do most breeders wait until to breed a filly?
3 years or older
what type of breeders are mares?
seasonally polyestrus long day breeders
when is the mare’s breeding season centered around?
June 21st
what does increased day length in early spring lead to from the hypothalamus?
increase in GnRH
how long is the estrous cycle in the mare?
around 21 days
what are most of the mare ovaries like in winter?
small and firm with not palpable follicles or functional luteal tissue
what percentage of mares do not undergo anestrus and continue to cycle in winter?
20-25%
what happens with behavior and ovulation in the fall transition period?
behavior and ovulation become more erratic
what does increased GnRH from the hypothalamus lead to in the spring transition?
gradual rise in LH but not enough to ovulate
persistent follicles, prolonged estrogen production and irregular/lengthy ovulation periods
how are mares housed to advance their first ovulation to breed them earlier for the racing and performance industries?
under 16 hours of light a day
starting December 1st
what do small and infrequent pulses of GnRH lead to in anestrus?
baseline LH and baseline high FSH that fluctuates randomly without negative feedback from ovarian inhibin and estrogen
what is the size of the follicle at ovulation and how much does it grow per day?
40mm
3mm per day
how long is diestrus usually in the horse estrous cycle?
14-15 days
what does the variability of the length of estrus depend on?
size of follicles present on mare’s ovaries at the end of diestrus and length of time it takes to grow dominant follicle and grow it
what is the preovulatory luteinizing hormone surge like in the mare?
long and drawn out
can last over a week
how rapid is ovulation?
complete evacuation of follicular fluid takes 2-7 minutes
when does ovulation occur compared to estrus?
within 48 hours of the end of estrus
how often to double ovulations occur?
16% of time
what horse breeds are more likely to have double ovulations?
thoroughbreds
warmbloods
what does the luteal phase begin with?
formation of progesterone-secreting corpus luteum
is estrus behavior indicative of high estrogen levels?
no, absence of high progesterone
what can diestrus ovulations lead to?
prolonged diestrus if resultant corpus luteum is too immature to respond to endogenous release prostaglandin
what are the physical changes during estrus?
mucous membranes of vulva and vagina moist and hyperemic
cervix edematous, relaxed, dilated
uterus flaccid and edematous
what are the physical signs of diestrus?
pale, dry vaginal mucous membranes
tightly closed, narrow, tubular cervix
increased tubularity of the uterus
what are the ovaries like in anestrus?
small and firm with no palpable follicles or functional luteal tissue
what does testicular size correlate with?
quantity of sperm produced
what should the total scrotal width be?
at least 8cm
how are the stallion testicles oriented?
long axis horizontal
tail of epididymis directed caudally and head directed cranially
why is the head of the epididymis hard to palpate?
flattened nature
cremaster muscle lies on top of it
what is the normal time frame for testicular descent into the scrotum?
by birth up to 6 months
when does puberty occur for the stallion?
12-18 months of age
when does sexual maturation occur for the stallion?
6 years of age
does the reproductive activity of the stallion decrease in winter?
somewhat, not as great as what happens in mare
reduction in testicular size and daily sperm output
what is the volume of the stallion’s ejaculate?
20-150 cc
what is the concentration of the stallion’s ejaculate?
50-250 million sperm per ml
what is the percentage of morphologically normal sperm in the average stallion’s ejaculate?
50%
where does the stallion ejaculate into?
directly into uterus through relaxed cervix
what is ejaculation accompanied by?
flagging of tail due to contraction of bulbospongiosus muscle
what is the main drawback to pasture breeding?
possibility of injury to mares and stallion
with in-hand breeding, how often are mares bred?
once day until they no longer show signs of heat
what are the main disadvantages of in-hand breeding?
failure of heat detection
breeding more frequently and earlier in the estrus than the stallion probably would on his own
what are the options of semen for artificial insemination?
fresh semen
shipped cooled semen
frozen semen
when using frozen semen, when must insemination be performed?
12 hours prior to or within 6 hours after ovulation to maximize pregnancy rates
what is non-return to estrus behavior at 17 to 21 days postovulation strongly suggestive of?
pregnancy
when can pregnancy in the mare be palpated?
28-30 days postovulation
embryonic vesicle large enough to be palpated per rectum
day 18 increased tone strongly suggestive
when can pregnancy in the mare be diagnosed via ultrasound?
day 14: embryonic vesicle
heart beat visible around day 25
how are sperm transported mainly to the oviducts?
uterine contractions
fertilization must occur no later than ______________ after ovulation to result in a viable embryo
12 hours
when does the embryo enter the uterus?
day 6 post-ovulation
what does the embryo secrete once it reaches the compact morula stage?
prostaglandin E2
what does prostaglandin E2 from the embryo do?
relaxes smooth muscle fibers in the wall of the oviduct
allows embryo’s passage into uterus
when does the embryo migrate constantly through the entire uterus?
until day 15
what causes the embryo to be immobilized at day 15?
sudden increase in myometrial tone and increased size of embryo
what is migration of the embryo throughout the entire uterus necessary for?
maternal recognition of pregnancy
when is the yolk sac stage?
days 11-21
when is the allantoic sac stage?
days 21-40
what does the equid fetus do around day 35 that is unique?
form endometrial cups: specialized cells invade deeply into adjacent maternal endometrium
cells proliferate
what cells form the endometrial cups?
trophoblastic cells from fetus
when are the endometrial cups active?
form day 35
around day 40 to day 120 of gestation
when are the placental attachments complete?
day 150
is placental transfer of large protein molecules possible in the equid placenta?
no
what is required to provide adequate nutrient and gas exchange for a single fetus?
entire endometrial surface
luteal progesterone is necessary to maintain pregnancy until about day ____
80
when do luteal progesterone levels peak?
about day 100
what is produced from the fetoplacental unit to maintain pregnancy?
5 alpha pregnanes mainly: dihydroprogesterone
not progesterone
when does the fetoplacental unit start to produce estrogens?
day 50
what is the gestation length of mares?
about 11 months: 342 days +/- 2 weeks
320-400 days
what are estrogens levels during gestation?
high in late gestation
begin to fall just before parturition
what are some signs of impending parturition?
relaxation of pelvic ligaments and tailhead
elongation of vulva
fullness of udder and leaking colostrum
how long does the first stage of labor last?
1-4 hours
what happens in the first stage of labor?
cranial portion of fetus rotates into dorsosacral position with head and limbs extended
early uterine contractions
cervical dilation and relaxation
how long does the second stage of labor last?
20 minutes
10 minutes to an hour
what happens in the second stage of labor?
active abdominal contractions
caudal portion of fetus now rotates into dorsosacral position
delivery of foal
how long does the third stage of labor last?
up to 3 hours post foaling
if the placenta is not expelled within _____________ it is considered retained and treatment is begun
3-6 hours
when should the foal stand?
within one hour of being born
when should the foal nurse?
within 2 hours of being born
what should the mare uterus be like by day 15 postpartum?
no fluid in uterine lumen
what is “foal heat”?
the first estrus after foaling
what caslick index values are associated with a normal anatomic arrangement/better fertility?
less than 100
approaching 150 is worse
what can incompetence of the vestibulo-vaginal seal/sphincter lead to?
pneumovagina
endometritis
reduced fertility
what does the cervix do during copulation?
lubricates vagina
what does the cervix do to prevent infection?
flushes out foreign material and bacterial contamination
protective seal during pregnancy and diestrus
what is the clitoral fossa important for in the mare?
contagious equine metritis testing
the mare uterus has prominent ________________ folds
endometrial
where do the corpora lutea protrude into in the mare?
ovarian tissue
not to ovarian surface: cannot palpate per rectum
what is the seasonality of mare breeding primarily controlled by?
photoperiod
when do mares transition?
autumn
spring
when is a mare in anestrus?
winter
what hormones control the seasonality of the mare’s estrous cycle?
melatonin: pineal gland
decreases GnRH
what might mares have during the autumnal transition?
reduced fertility
persistent, anovulatory follicles
possibly prolonged periods of estrus
when is the mare breeding season?
April to Sept-Oct
how does length of estrus vary with season?
follicular growth faster at peak of breeding season
duration of estrus shorter as season progresses
size of ovulatory follicle tends to be smaller at peak season
when does LH peak with mares?
1-3 days post ovulation
how predictable is ovulation relative to onset of behavioral estrus?
not as predictable as other species
do mares have a countercurrent exchange mechanism for luteolysis?
no
can mares ovulate in the face of high progesterone?
yes sometimes
what are the behavioral signs of diestrus?
ears pinned
tail switching
squeal
kick, bite, strike
what does the uterus look like during estrus?
flaccid, edematous folds
“spoking” pattern on ultrasound
what is the erectile tissue enclosed by?
tunica albuginea
what is the erectile tissue in the equine penis?
corpus carvernosum
corpus spongiosum
when do stallions have a reduction in testicle size and daily sperm output?
late autumn and winter
what mounts are used to collect semen?
estrus mare
ovariectomized, estrogen treated mare
phantom
what is the motility of stallion sperm?
60/40%
total/progressive
what is the total breeding time of equines?
2-5 minutes
what are the options for natural breeding?
pasture breeding
in-hand breeding
how often are mares bred in in-hand breeding?
every other day until they go out of heat
what is the minimum insemination dose for cooled semen?
500 million live, progressively motile sperm
what is the insemination window for shipped cooled semen?
36-48 hours before to 12 hours after ovulation
what is unique to equids with their oviducts and embryos?
differential transport of embryo vs oocytes
oocytes stay in oviduct
what do the endometrial cups produce?
equine chorionic gonadotropin
what does equine chorionic gonadotropin do?
has luteinizing hormone like activity
causes ovulation and luteinization of follicles: form secondary and accessory corpus lutea
what do endometrial cups do?
prevent return to estrus even if pregnancy is lost
what type of placenta do equids have?
diffuse, microcotyledonary, epitheliochorial
what is the progesterone source during the second luteal response?
endometrial cups’ eCG causes resurgence of primary corpus luteum
when is luteal progesterone necessary to maintain pregnancy until?
day 80
how can milk be used to predict parturition?
increase in calcium just prior
drop of pH to <6.4 within 24 hours of parturition
when does the first stage of labor end?
chorioallantois ruptures, releasing allantoic fluid
what is a red bag delivery?
premature separation of outer placental membrane from uterine wall may lead to protrusion of the intact fluid-filled chorioallantois through the vulva
why is a red bag delivery an emergency?
detachment leads to a rapid decrease in oxygen transport to fetus
what can failure to treat retained fetal membranes lead to?
metritis
endotoxemia
death
how long is estrus?
6-7 days usually
do double ovulations increase the chance of conception?
yes
where is PGF2alpha released?
into systemic circulation
what is the uterus like in diestrus?
firm tone
uniform echogenicity on ultrasound
what do the ovaries look like in estrus?
one or more large follicles palpable and visible on ultrasound
what do the ovaries look like during diestrus?
various sized follicles present
corpus luteum visible with ultrasound
what is at the cranial dorsal aspect of each testis in the stallion?
spermatic cord
what is another name for the glans penis?
corpus spongiosum glandis
what can the urethral sinus have?
“bean”
where is sperm storage?
tail of the epididymis
what accessory sex glands do stallions have?
ampullae
seminal vesicles
prostate lobes
bulbourethral glands
what is the longevity of fresh stallion semen?
48 hours
what is the morphology of stallion semen?
50% normal
how long does intromission and ejaculation take?
less than 1 minute
what is a downside of repeat breeding?
can lead to breeding-induced endometritis
where is semen deposited in artificial insemination?
body of uterus
tip of uterine horn on the side of ovulation
when is the embryo covered by a capsule?
until days 21-22
when and where does the fetus attach?
day 15-16
base of a horn
when is the fetus highly mobile?
60-120 days
what are the progesterone sources throughout pregnancy?
1st luteal response: embryo migration prevents demise of corpus luteum
2nd luteal response: endometrial cups’ equine chorionic gonadotropin cause resurgence of primary corpus luteum
3rd luteal response: equine chorionic gonadotropin causes ovulation and luteinization of follicles to form secondary and accessory corpus luteums
fetoplacental unit
before what day of gestation is non-viable?
day 300
between what days of gestation is considered premature?
day 300-320
at what point of labor is it considered dystocia?
beyond one hour
greater than 30 minutes increases risk of injury/death to foal
by what day after parturition should the uterus be contracted down to non-pregnant size?
day 30
when does foal heat usually occur?
days 5-12 postpartum
