Repro Physiology Flashcards
What is the first sign of pregnancy for palpation?
Bulge on the ventral aspect of the horn
What is responsible for triggering ovulation?
LH
What suppresses LH?
Progesterone
Puberty occurs around ______
2 years of age
Polyestrus
Long day breeders
- northern hemisphere: spring/summer
- southern hemisphere: fall/winter
- cycle from March-October (20% will cycle year round)
Mare will ______ during the breeding season
Repeatedly cycle
- recurring estrus on a predictable interval until pregnant or season ends
Estrous cycle
From ovulation to subsequent ovulation
Follicular phase
Estrus
- estrogen is dominant
- estrus ends 18-24 hrs after ovulation
Luteal phase
Diestrus
- starts with ovulation until luteolysis
Ovulation to ovulation is ______
21 days
Estrus
Behavioral signs associated with impending ovulation
- receptivity to male
- occurs when progesterone is low (after luteolysis)
Give _____ if you do not want a mare to show estrus signs
Progesterone
Jump mare
Mare that has had her ovaries removed, so progesterone levels are nonexistent
- will be passive whenever a stallion is presented
- can collect stallions whenever needed
Entire estrous cycle lasts
20-24 days
Estrus lasts
4-7 days
- single follicular wave is most common in equines
- cows have 2-4 waves
- dominant hormone is estrogen
Follicular wave
Cohort of immature primordial follicles that emerge until 1 becomes dominant and suppresses all others
Diestrus lasts
14-15 days
- consistent length in equines
- dominant hormone is progesterone
Mares ovulate _______ before going out of heat or estrus
24-48 hrs
Ovulation
Occurs prior to the end of estrus
- follicle size at ovulation is generally 40-45 mm
- size can be breed dependent
- double ovulation occur 16% (twinning)
______ follows ovulation
Luteal phase
Mares ovulate_____, toward the ______
Inward; ovulation fossa
Predicting ovulation
Used for breeding purposes
- follicles grow 3-4 mm per day
- follicle becomes soft
- loss of spherical shape with development of apex
- serrations in granulosa layer
Teasing with stallion - estrus
- tail raise
- squat, tip pelvis
- urinate
- evert clitoris
Exam of ovaries - estrus
- large follicle, may be soft
- follicle may be triangular w/ scalloped edges on US if mare is near ovulation
- no CL on US
Exam of uterus - estrus
- relaxed w/ soft texture
- edematous endometrial folds visible on US
Exam of cervix - estrus
- shortening, widening
- relaxed w/ soft texture
- pink and drooping on vaginal floor
- lumen open 1-3 fingers on digital exam per vagina
Teasing w/ stallion - diestrus
- switch tail
- kick, squeal
- attempt to bite
- move away
Exam of ovaries - diestrus
- presence of CL on US
- follicles of varying sizes, may be large
Exam of uterus - diestrus
- firm texture (good tone)
- uniform echogenicity on US
Exam of cervix - diestrus
- long and narrow, firm texture
- pale, dry, centrally located in cranial vagina
- closed lumen on digital exam
Seasonality in mares is regulated by ______
Photoperiod
- improved efficiency during periods of increased daylight
- length of photoperiod modulates GnRH secretion
During short days, _____ secretes ______
Pineal gland; melatonin
- suppresses GnRH
During long days ______
Little melatonin is released, suppression is removed
Melatonin
Released when it is dark!
- inhibitory effect on GnRH in the mare
- secreted by pineal gland, under control by retina’s detection of light via photoreceptors
Melatonin’s effects
- short days: pineal gland secretes more melatonin so GnRH is inhibited (anestrus)
- long days: pineal gland releases little melatonin and GnRH is not inhibited (mare cycle’s)
Vernal transition
Period of time during spring and fall when mare is transitioning from anestrus to cyclicity and reverse in the fall
- ambiguous signs of estrus seen
- ends w/ first ovulation of the season
Spring transition
- erratic estrus behavior
- erratic follicular growth
- anovulation
- improper breedings
Stallion repro physiology
Puberty at 2 years
- seasonal pattern of sperm production is evident, but they never stop producing
_____ is the physiological breeding season for horses
April-Sept
- best fertility in May-July
_____ is autumn transition
Oct-Nov
- going out of season
______ is winter anestrus
Dec-Jan
- no signs of estrus
- little to no follicular activity
_____ is spring transition
Feb-March
- coming into season
Imposed breeding season
Jockey club states that all foals are 1 year of age on Jan 1st
- larger foals top the sales
- breeders want to have the largest foals
- pushed to breed mares when environmental cues say they shouldn’t
Lighting schemes
Place mares under lights beginning Dec 1st (16 hrs daily)
- continue for 60 days
- photoperiod is manipulated
- mares enter vernal transition sooner –> first ovulation sooner
Foal heat
First postpartum estrus
- occurs around 10 days postpartum
- fertility is adequate in most cases
Backing up a mare
Have her foal earlier in subsequent years than the current year
- gestation length of approx 340 days
- to keep her around the same foaling date, she would need to conceive within 25 days of foaling
