Equine - Anatomy and Reproductive Physiology Flashcards
What type of uterus does the horse have?
bicornuate or Y-shaped
What is the role of the broad liagament in the horse?
It suspends structures within the abdominal cavity
What is contained within the broad ligament?
arteries, veins, nerves, and lymphatics
What does the mesovarium support?
the ovaries
What does the mesosalpinx support?
the oviducts
What does the mesometrium support?
the uterus/cervix
How many folds are within the cervix?
5-10 longitudinal folds
What is the cervix made up of?
muscle
How large is the cervix?
6-7cm in length
The cervix cannot and should not every be ________.
retracted
What separates the vagina and the vestibulum?
transverse folds
Where should 2/3 of the vulva be located?
below the pelvic brim
What direction is the vulva oriented in?
vertical or near vertical orientation
What is the clitoris made up of?
a fossa and 3 sinuses (medial and lateral)
What are the three barriers to the internal reproductive tract?
vulva, intact vestibulovaginal sphincter, and cervix
What do the three barriers of the internal reproductive tract protect it from?
fecal contamination, windsucking, and bacterial ascension of the cranial repro tract
What is the shape of the equine ovary?
it is kidney bean shaped
Where does ovulation occur?
at the ventral ovulation fossa
Where is the medulla located in the equine ovary? The cortex?
the medulla is on the outside, the cortex is on the inside
When does puberty occur in a mare?
12-24 months - average is 15 months
When does a mare reach maturity?
by 3 years of age
How would you classify a non-pregnant mare’s estrous cycle?
long day, seasonally poly estrus
What are the phases of seasonality in the mare?
vernal transition (spring), breeding season, autumn transition, and winter anestrus
Winter anestrus is due to ____ days.
short
What are the reproductive hormones like during winter anestrus?
low levels of LH, estrogen, and progesterone
If there are follicles, what size are they during winter anestrus?
less than 5-10 mm in diameter
What type of firmness is the reproductive tract during winter anestrus?
flaccidity
How long is vernal transition?
1-2 months - average 55-60 days
What estrus behavior occurs during vernal transition?
erratic estrus behavior
When does vernal transition naturally occur in the Northern Hemisphere?
from february to april
a.
increased daylight
b.
recognized by retinal photoreceptors
c.
pineal gland
d.
decreased melatonin secretion
e.
hypothalamus
f.
increased GnRH secretion
g.
hypophyseal-portal circulatory system
h.
anterior pituitary
i.
increased LH and FSH secretion
What occurs during early vernal transition?
minor and major anovulatory waves - increased FSH and LH
What size are the follicles in early vernal transition?
less than or equal to 30 mm
What occurs during mid to late vernal transition?
There are major ovulatory waves (increased LH and decreased FSH), selection of the dominant follicle, ovulation, and commencement of normal cyclicity
When does average ovulation occur for a mare not under a lighting program?
April 15th
What are some additional findings associated with vernal transition?
varying degrees of uterine edema, +/- intrauterine fluid, erratic and prolonged estrus behavior
How long is autumnal transition?
1-2 month duration - decreasing day length
When does autumnal transition occur?
it is highly variable - it occurs somewhere between september and December
What is autumnal transition the result of?
opposite neuronal and hormonal events
What are autumnal follicles?
hemorrhagic and fibrin filled anovulatory follicules due to failure of ovulation
How long is the estrous cycle of the mare?
18-24 days - average is 21 days
How long is diestrus (luteal phase)?
14-17 days
How long is estrus (follicular phase)?
4 -7 days
Typically, how many follicular waves are there in a mare?
two
True or false: Follicles are only present during estrus.
false - they are present during both estrus and diestrus
When does diestrus occur?
after ovulation
What structure is formed during diestrus?
the corpus hemorrhagicum
When does the corpus hemorrhagicum mature and what does it become?
5 days after formation; it becomes the corpus luteum
What form may the corpus hemorrhagicum be?
it may be solid or cystic - both are normal
What hormone influences diestrus?
progesterone (P4)
What hormone influences the end of diestrus?
Prostaglandin
What behavioral signs does a mare exhibit under the influence of progesterone?
tail clamping/swishing, kicking, striking, or biting, and squealing
What physical infleunce does progesterone have on the reproductive tract?
There is no uterine edema. Tight, narrow, pale, and dry cervix up off the vaginal floor (high, dry, and tight)
What influence does progesterone have on the reproductive hormones?
it inhibits anterior pituitary LH release and hypothalamic GnRH production - i.e it inhibits secondary ovulations (usually) and postpones follicular maturation and growth
True or False: Progesterone causes immune suppression to the reproductive tract.
true
What influence does progesterone have on the glands?
glandular development and secretion
How many waves of follicular activity occur during diestrus?
1-2 waves - FSH activity
What occurs during diestrus?
recruitment and initial follicular growth
When does luteolysis typically occur?
around day 14 of diestrus
What occurs during rapid luteolysis?
There is a decline in P4 that is first detectable 4 hours after release. There is a significant decrease in P4 within 40 hours. The lutel structure regresses.
a.
induction of endometrial E2 receptors
b.
follicular E2 binding induces endometrial OT receptors
c.
OT binding induces endometrial prostaglandin production
d.
travels through the systemic circulation to CL
e.
vasoconstriction of utero-ovarian vessels
f.
luteal ischemia
What is estrus?
the period of continued follicular growth, dominant follicle selection, and further growth and maturation of the dominant follicle(s)
What is follicular growth under the influence of?
rising LH and FSH
What hormone can follicular thecal and granulosa cells produce and how does that hormone affect LH secretion?
estrogen which provides positive feedback on LH secretion
What size is a dominant follicle in a mare?
25 mm
What hormone does a dominant follicle produce and how does it affect FSH levels?
inhibin tells AP to stop releasing/producing FSH and therefore decreases FSH levels
Follicles secrete estrogen. How does that influence FSH and LH levels?
estrogen decreases FSH and increases LH
What happens to the non dominant follicles during estrus?
they go through atresia
What behavioral signs does a mare exhibit under the influence of estrogen?
Stallion receptivity, raising tail, winking, passive urination, and squatting
What reproductive changes does a mare undergo under the influence of estrogen?
uterine edema and cervical relaxation
What receptors do dominant follicles have and how many mm do they grow a day?
They express granulosa LH receptors and grow 3-5 mm/day
What is the preovulatory size of follicles in light breeds?
30-45mm
What is the preovulatory size of follicles in Drafts and Friesians?
greater than 40-50mm
What is the preovulatory size of follicles in Ponies/Minis?
less than 30mm
Pending ovulation, what occurs to the follicle, granulosa cell layer, and uterus?
The follicle begins to point and lose shape becoming irregular and then softens. The granulosa cell layer thickens. Uterine edema often decreases
In relation to estrus, when does ovulation typically occur?
routinely 24-48 hours prior to the end of estrus
