Introduction to Equine Reproduction Flashcards
Mares are seasonally polyestrous and have multiple estrous cycles when?
in the spring and summer
Seasonality is triggered by
increasing day length
Each estrous cycle is about how long?
18-23 days long (average = about 21 days)
What are the two phases of an estrous cycle?
estrus and diestrus
Estrus
when the mare is receptive to the stallion
-aka heat
What is estrus under the influence of?
estradiol
Diestrus
when the mare is not receptive to the stallion
What is diestrus under the influence of?
progesterone
Anestrous
when the mare is not cycling
Each estrus period is usually about..
3-7 days long
Each diestrus period is usually about..
12-18 days long
Ovulation occurs when?
24-48 hours before estrus ends
Fertilization of the oocyte occurs in the…
oviduct
The oocyte remains fertile for about
12-18 hours after ovulation (window of opportunity once ovulation occurs is small)
Once in the mare, normal sperm should remain fertile for about…
48-72 hours if fresh
The best time to breed a mare is…
24-48 hours before ovulation
The best time to breed a mare in the estrus cycle is..
the second day of estrus and every other day until estrus ends
From day of conception to delivery of a normal foal, gestation length in mares…
can range from 10.75-12 months
If a mare conceived on May 15 of 2023, when would you expect her foal?
mid/late April 2024
When mares conceive twins, it is considered…
normal but not desirable
About how many foals (all breeds) are born each year in the US and Canada?
100,000-150,000
If the annual foal crop in 2024 is 150,000 about how many mares were bred in 2023?
200,000-225,000 (55-60% live foal rate)
Why is live foal rate important?
-the more mares you have to breed to get more foals, the more expensive
-a live foal is needed in order for the stallion owner to get paid
-helps us understand and do better with reproductive efficiency
Broodmare
any mare intended for breeding
Barren mare
mare was bred and didn’t get pregnant
Maiden mare
a mare being bred or producing a foal for the first time
Rested mare
mare has had foals but is not bred or pregnant one year
Wet mare
mare that is lactating
A “breeding system”
the management process intended to result in a foal
What is the breeding system regulated by?
breed associations
-some systems/procedures may be completely prohibited
-some systems/procedures may be allowed under some circumstances -
Two main types of breeding systems:
-assisted reproduction (AI, embryo transfer, etc.)
-natural service
Assisted reproduction systems have…
-large human intervention
-breed/registry may include restrictions, require fees and permits
Artificial insemination
semen is collected from a stallion and later inseminated in a mare
Types of semen:
-fresh
-cooled
-frozen
Fresh semen
used in a few hours, usually on farm or local
Cooled semen
5 degrees C
-shipped overnight
-most common in the US
Frozen semen
frozen in liquid N
-stored frozen
-shipped frozen
-can have it for years
-some stallions’ semen does not tolerate being frozen
Typical stallion management for AI:
-train stallion to use phantom/dummy
-train stallion to use artificial vagina
-collect semen as needed
What is a common collection schedule for AI for stallions?
-3-4 times/week: M, W, F, maybe Sat
-if freezing, when the stallion is available
What do people typically do with the first stallion collection?
test collect to determine best conditions, temp, extenders, freezability, etc.
When collecting semen to breed mares:
-evaluate semen: volume, concentration, motility, morphology
-extend and divide doses
-cool and ship or freeze and store/ship
Typical mare management for AI
-heat detection program (teasing, vet exams, etc.) to forecast ovulation time
-order semen
-schedule for vet insemination
-check mare for ovulation (vet) in 24 hours
When do we want to inseminate AI for a mare?
close to ovulation
Embryo transfer
A donor mare is bred (usually AI) and ovulation is tracked. The embryo is collected and inserted into a recipient mare that will carry the foal to term
When is the donor mare flushed for the embryo?
about day 7
Who is the official dam of the foal from embryo transfer?
the donor mare
Recipient mare in embryo transfer:
-synchronized with donor, ideally ovulate at the same time
-embryo is transferred after collection
Success with fertile mares in embryo transfer is as high as
85%
How to choose a recipient mare for ET:
-reproductively healthy
-raised a previous foal (good maternal behavior)
-same size as donor
Natural service is allowed by…
all breed registries
-it is the only one allowed in the Thoroughbred industry
Natural service is also known as:
live cover
Hand-mating live cover
-mares travel to where the stallion is
-mares wear a neck cover/tail wraps/boots to protect the stallion and her during breeding
-mare is teased and an ultrasound is done to check estus cycle
-mare and stallion are being held and possibly assisted while mating occurs
Pasture mating
stallion breeds mare(s) in an enclosure
-a mare may be taken to a stallion and turned out with him for a certain period of time
-more commonly a stallion is put in with a herd of mares at the beginning of the breeding season and left there until the breeding season is over
Advantages of pasture mating
-less stressful
-less work for people
-no risk of injury to people
-effective (allowed by registries)
-allows “extensive” management system
-lower cost (labor/equiptment)
Disadvantages of pasture mating
-more risk of infection transmittal
-more risk of injury to all horses involved (including foals)
-no info on conception rate until end of season
-less info on breeding dates (then won’t know foaling date)
-fewer mares per stallion
-reduce genetic choices
Advantages of hand mating
-known breeding date
-genetic choices
-better hygiene
-less risk of injury to the horses (especially foals)
-ability to follow pregnancy rates
-allowed by all registries
-collect semen for evaluation
-more mares per stallion (with high management)
Disadvantages of hand mating
-more labor before and during breeding
-more stressful for mare (may need to travel, or leave foal)
-more risk for people
-higher cost (more labor and facilities)
Advantages of AI
-use of competition horses
-more mares/season
-more mares/ejaculate (less stressful for stallion)
-more genetic choice
-mare and stallion in different places (better biosecurity)
-less risk of injury for people and horses
-more opportunities to evaluate semen
Disadvantages of AI
-cost (shipping, vet procedures, equipment, access to more expensive stallions)
-genetics (could decrease genetic diversity if too many mares are bred to one or two stallions)
-scheduling and logistics are challenging
-more expertise needed
-registry requirements (fees or not allowed at all)
Advantages of embryo transfer
-preserve genetics of mares that are not capable of having a foal
-obtain foals from mares that are currently competing
-may be able to obtain several foals from 1 mare/year
Disadvantages of embryo transfer
-expertise and equipment needed
-expense (at least two mares)
-registration and reporting requirements
