Reproduction Flashcards
mare begin pubert at…
can become pregnant at…
18 months
2 years old
equine estrous cycle
- seasonal polyestrus (long day breeders) between april and july
- estrous cycle is 21 days
- duration of estrus is 7 days
- ovulation occurs near end of estrus
estrus
- when mare shows sexual receptivity to stallions
- stronger signs as ovulation nears
- controlled by estrogen
- behaviour=raising tail, urination, posturing, winking
diestrus
- when mare rejects stallions
- 14-16 days, behaviour starts within 12 hours of ovulation
- controlled by progesterone
- behaviour=pins ears, clamps tail, switches tail, moves away, kicks
hormonal changes
estrogen, LH, and FSH high during estrus, with progesterone low; progesterone high and fsh, lh and estrogen low; FSH peaks twice at beginning and end of diestrus, and PGF2 spikes at end of estrus
hypothalamus
‘surge center’ where GnRh is released into pituitary gland and receives signals from ovary
-also commands release of LH and FSH from pituitary
pituitary
transport LH, FSH, and GnRH down to ovary
ovary and follicles
cause +ve feedback with hypothalamus or -ve with pituitary gland’s secretion of GnRH and FSH via inhibin
endocrinology of estrous cycle
GnRH stims FSH and LH from anterior pituitary
- FSH stims follicle development
- dominant follicle produces estradiol and inhibin
estrous cycle and estradiol, inhibin, and prostaglandin
estradiol=LH secretio, estradiol-receptor sensitivity on dominant follicle
- inhibin=decreased GnRH and FSH; leads to LH surge and ovulation
- prostaglandin (PGF2) causes lysis of CL and allows for ovulation
rule of thumb for estrogen/progesterone
high progesterone=suppresed LH
high estrogen=suppressed FSH
seasonality
transition periods in spring=vernal and fall=autumnal
- time of LOW reproductive activity, no clear patterns, and delayed ovulation
- normal cycles in april/may, september/october
- controlled by photoperiod
seasonality influences
age, body condition, disease
-2 years old cycle in june-august
-mares over 20 have few cycles in june or july or no ovary activity
over 25 seldom cycle
seasons for mares
summer=natural breeding season, fall transition, winter=anovulatory season, spring transition
photoperiod
controls ovarian activity through PINEAL gland and melatonin production
decreased daylight=…
increased=…
=increased melatonin production=decreased GnRH, FSH, and LH
=decreased melatonin production=incrased GnRH, FSH, estrogen, and LH
reproductive management
- artificial insemination, follicle stimulation, embryo transfer
- usually requires manipulation of estrus cycle
hormonal therapies
-manipulation of seasonality, normal cyclicity, estrus synchro, modify sexual behaviour through elimination of estrus, induction of lactation, manage high risk pregnancy, abortion
goals of manipulation
- induce early start of transitional period using lighting regimes and GnRH administration
- shorten duration of transitional period using and withdrawal of progesterone
- time estrus and ovulation with semen availability
- estrus synchro btw embryo donors and recipients
getting mares ready for breeding
teasing through exposure to males
- in early season examine to determine which mares are transitional and which cycling
- plan hormonal manipulation
- determine if CL present, follicle size, quantify uterine edema
examine uterus by
rectal palpation or ultrasound
stallion puberty
begins at 18 months, seasonal sperm production controlled by GnRH, peak sperm in july
stallion breeding soundness exam (BSE)
performed after 2 years: physical exam and semen collection and evaluation (morphology, concentration, motility)
breeding basics
breed mare when in estrus, so ovulation occurs within 48 hours of breeding
- fertility is function of quality of mare, timing of insemination, and dose/quality of semen
- liver cover=breed mares every other day
cooled semen for
=breed once, when mare has 35 mm follicle, breed 24 hours later
frozen semen
either fixed time insemination around 28-44 hours after ovulation induction
teasing and estrus behaviour
-leaning or moving in, raising tail, winking, urination, posturing
lordosis
aka mating posture of female
conception
per cycle rates 60-70%
per season pregnancy rates 80-90%
-no artificial reproductive tech allowed in Thoroughbreds, varied for other breeds
pregnancy
normal range of 320-365 days
preterm=300-320 days
-progesteron maintains pregnancy detection
-ultrasound best
twins…
must be reduced before day 35, danger to mother and foals
parturition
-predicted by electrolytes in milk change
-72 hours=increase in calcium and magnesium
-24 hours=decrease in Na and increase in K
colostrum in udder (waxing up)
-occurs in 3 stages
-90% foalings proceed without intervention of birth
-only intervene when foal or mare are in great danger
stage 1 parturition
coordinated forceful uterine contractions
- cervical dilation
- visibly lasts about 4 hours
- behaviour is typical of colic: sweating, cramping, up down behaviour, drippin or streaming milk
stage 2
rupture of chorioallantois, aka water breaks
- delivery of fetus
- lasts 5-30 minutes
- once water breaks amnion (bluish) should be visible at vulva
- delivery occurs in 30 minutes or less
- normally see 2 legs facing down followed by muzzel
emergency during stage 2
red bag: premature separation of placenta from uterus
-requires immediate attention because foal asphyxiates
stage 3
passage of placenta, takes up to 2 hours, greater than 4 requires treatment
normal foal behaviour
sternal recumbency: 1-2 minutes suckle reflex: 2-20 minutes stand in 60 minutes nurse in 2 hours, for up to 7 times per hour urination within 8-12 hours
weaning
free-living weaning occurs at 8-9 months
- in domestic occurs at 4-6 months
- results in increased vocalization, locomotion, and salivary cortisol
- weaning stress can be reduced by introducing adults
- post-weaning handling can improve handling up to 18 months later
