Equine Breeding Management Flashcards
(42 cards)
What is the goal birthdate of racehorses? How is this most commonly reached?
January 1st
advance transitional or ovulatory periods from April to February to have mares pregnancy by February or March (~340 days of gestation)
How is photoperiod manipulated to get mares to delivery around January 1st? In what 2 ways is this done?
put mares under lights by December 1st
- stall - 16 hours of light (in effect by 60-70 days) or skeletal light exposure for 1-2 hours beginning 8-9.5 hours after the onset of darkness
- light mask - blue light directed in one eye for horses on pasture (Equilume)
What are 4 options for medically managing seasonal anestrus in horses?
- GnRH - administer BID-TID (response related to follicle size)
- hCG - induces large follicles to ovulate by mimicking an LH surge
- progesterone/progestin - synchronization, decreases LH (controversial)
- dopamine antagonists (Domperidone, Supriride)- increases plasma prolactin, acting directly on the ovary
What pre-treatment can potentiate dopamine antagonists effects?
estradiol
What are the 3 hormone treatments used to manipulate cycling mares? When are they used?
- PGF2a - 5-14 days after ovulation; induces luteolysis with missed insemination (will cause abortion in pregnant mares)
- GnRH. hCG - 20 days after ovulation; stimulates natural LH surge to induce an early round of ovulation
- PGF2a/oxytocin - evacuates fluid from endometritis and causes smooth muscle contraction
How is short-cycling performed in mares? What are the 2 most common options used? What timing is required?
use of luteolytic PGF2a to terminate the luteal phase before the normal release of endometrial PGF2a
- Dinoprost
- Clopostenol
> 5 days after ovulation - mare will be insensitive to a single dose any earlier while in early diestrus, but can still affect luteal function
What are 3 potential side effects to short cycling mares? How are the medications given?
- transient sweating
- abdominal cramping - SM contraction, looks like colic but is transient
- diarrhea
IM ONLY - VERY sensitive to IV due to reliance of systemic circulation to get PGF2a to the ovaries
What is required for inducing ovulation in mares? What are 2 options? When do each induce ovulation?
estrual mare with a follicle >30 mm diameter (large enough to ovulate)
- GnRH agonists (Deslorelin) - 40-42 hours
- hCG (LH-like action) - 36 hours, but has a larger average range —> not preferred
What is a possible side effect of using hCG to induce ovulation in mares?
human product may cause antibody formation that decreases effectiveness/efficiency
What 2 embolics can be used to manipulate equine estrous cycles? Why are they used?
- PGF2a - facilitate uterine clearance by stimulating myometrial contractions (Cloprostenol preferred due to longer half-life and less side effects)
- oxytocin - stimulates uterine smooth muscle contractions to evacuate uterine fluid (shorter half-life, 10-20 IU given SID-TID)
What 3 diseases are tested for before breeding horses?
- EIA
- Contagious equine metritis (CEM)
- EVA
(all can cause abortion!)
What are 2 options for natural cover breeding? What equipment is commonly used?
- bred on 2nd or 3rd day of estrus
- mated every other day until the mare is no longer receptive to the stallion
twitch, protective capes, neck apron, leg strap, Hobbles, kick boots, tail wrap, ovulation induction agent
What breed of horse only has one allowed way of assisted breeding? What is done?
Thoroughbred
reinforcement breeding - natural cover + aspiration of semen left in cranial vagina and insemination into uterus
Why is AI commonly performed for equine breeding programs?
- safety for stallions, mares, and personnel
- allows in-depth stallion management
- can pick from different mares
- allows horses for different regions to be used easily
What is the goal of using shipped-cooled semen for equine AI? What dose is used? When will managed ovulation occur?
one breeding per cycle
at least 500 million motile sperm cells (more if available!) - similar pregnancy rates compared to natural cover and fresh semen AI
within 24-48 hours after AI —> important for timing of semen delivery
How is shipped-cooled semen prepared before AI?
- diluted with semen extender to 25-50 million sperm/mL
- cooling rate of -0.3 C/min —> no need to warm before, used to minimize metabolic rate to keep sperm alive longer
What is the best timing for delivering shipped-cooled semen? What 2 options for inducing ovulation and their pros/cons?
inform stud farm when the mare is in estrus (>30 mm follicle) to shep extended semen overnight or counter-to-counter
- breed and then induce with hCG or Deslorelin - semen is confirmed, but mare may not ovulate within 40 hours and sperm will not last, requiring more sperm from stud far
- induce ovulation a day before AI - gives sperm more time, but sperm may not be able to be collected and the mare will have to be short cycled to start again
(expected 85-90% ovulation within 48 hours!)
In what 2 ways does frozen semen differ compared to shipped-cooled semen?
- more variable pregnancy rates - mare tends to react more poorly to this type of semen and endometritis is more common
- lower minimum dose of 250 million motile sperm cells - more valuable stallions tend to have their sperm frozen, so there is a pressure to use the least amount possible
What are 2 options of protocol for AI with frozen semen? What way of insemination is preferred?
- one AI within 4-6 hours post-ovulation
- two AIs 12-16 hours apart with ovulation occurring between
transrectal-guided deep horn insemination - ensures the smaller (more valuable) dose has less distance to reach oocytes
What timing is preferred for AI with frozen semen? What should be done if ovulation is or isn’t detected?
mare in estrus (follicle >30 mm) —> induce ovulation at 4 PM and then perform first AI 24-30 hours after induction (4PM-10PM)
- 8 AM ovulation detected = second AI 40 hours after induction (8AM)
- 8 AM no ovulation = keep checking periodically and second AI after ovulation
(no risk of delayed shipment, already on site)
What are 2 recommendations for managing frozen semen for AI?
- higher doses per insemination
- at least 2 inseminations per cycle - one before and one after ovulation
What is considered a “problem” mare?
- abnormal estrous cycles
- fails to conceive for more than 3 cycles in one season
- early pregnancy loss within 60 days
(don’t forget the stallion!)
What is physiologic endometritis? Pathologic?
immune response to eliminate seminal plasma, excess sperm, microorganisms, and debris following breeding
becomes uncontrolled and reduces fertility
What signs are associated with endometritis? What cases require treatment?
typically indistinguishable +/- microorganisms in samples
excessive accumulation of PMNs and intraluminal fluid in the uterus
