Horse Breeding Covering the Mare

There are two general ways to "cover" or breed the mare: Live cover and Artificial Insemination (AI).

Live cover:
the mare is brought to the stallion's residence and is covered "live" in the breeding shed. She may also be turned out in a pasture with the stallion for several days to breed naturally. The former situation is often preferred, as it provides a more controlled environment, allowing the breeder to ensure that the mare was covered, and places the handlers in a position to remove the horses from one another should one attempt to kick or bite the other.

Artificial Insemination (AI):
the mare is inseminated by a veterinarian, using either fresh cooled or frozen semen. After the mare is bred or artificially inseminated, she is checked 16 days later to see if she “took,” and is pregnant. A second check is usually performed at 28 days. If the mare is not pregnant, she may be bred again during her next cycle.

Live Cover
When breeding live cover, the mare is usually boarded at the stud. She is "teased" several times with a stallion that will not breed to her, usually with the stallion being presented to the mare over a barrier. Her reaction to the teaser, whether hostile or passive, is noted. A mare that is in heat will generally tolerate a teaser (although this is not always the case), and may present herself to him, holding her tail to the side. A veterinarian may also determine if the mare is ready to be bred, by ultrasound or palpating daily to determine if ovulation has occurred.

When it has been determined that the mare is ready, both the mare and intended stud will be cleaned. The mare will then be presented to the stallion, usually with one handler controlling the mare and one or more handlers in charge of the stallion. Multiple handlers are preferred, as the mare and stallion can be easily separated should there be any trouble.

Artificial Insemination (AI)
AI has several advantages over live cover, and has a very similar conception rate: The mare and stallion never have to come in contact with each other, which therefore reduces breeding accidents, such as the mare kicking the stallion. AI opens up the world to international breeding, as semen may be shipped across continents to mares that would otherwise be unable to breed to a particular stallion. A mare also does not have to travel to the stallion, so the process is less stressful on her, and if she already has a foal, the foal does not have to travel. AI allows more mares to be bred from one stallion, as the ejaculate may be split between mares. AI reduces the chance of spreading sexually transmitted diseases between mare and stallion. AI allows mares or stallions with health issues, such as sore hocks which may prevent a stallion from mounting, to continue to breed. Frozen semen may be stored and used to breed mares even after the stallion is dead, allowing his lines to continue. However, the semen of some stallions does not freeze well, and live cover is sometimes the only option. It is important to note that the Thoroughbred industry does not allow AI, and all breedings must be live cover if the resulting foal is to be registered to race.

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A stallion is usually trained to mount a phantom mare, although a live mare may be used, and he is collected using an artificial vagina (AV), which is often heated to simulate the vagina of the mare. The AV has a filter and collection area at one end to collect the semen, which is then processed in a lab. The semen is then chilled or frozen and shipped to the mare owner. When the mare is in heat, a veterinarian introduces the semen directly into her via a syringe and pipette.

The Thoroughbred industry does not allow AI or surrogate dams. Surrogate Dams:
Often an owner does not want to take a valuable competition mare out of training to carry a foal. This presents a problem, as the mare will usually be quite old by the time she is retired from her competitive career, at which time it is more difficult to impregnate her. Other times, a mare may have physical problems that prevent or discourage breeding. However, there are now several options for breeding these mares. These options also allow a mare to produce multiple foals each breeding season, instead of the usual one. Therefore, mares may have an even greater value for breeding.

Embryo Transfer:
The relatively new method involves removing the mare's fertilized embryo a few days following insemination, and transferred to a surrogate mare. Gamete Intrafallopian Transfer (GIFT): The mare's ovum and the stallion's sperm are deposited in the oviduct of a surrogate dam. This technique is very useful for subfertile stallions, as fewer sperm are needed, so a stallion with a low sperm count can still successfully breed. Egg Transfer: An oocyte is removed from the mare's follicle and transferred into the oviduct of the recipient mare, who is then bred. This is best for mares with physical problems, such as an obstructed oviduct, that prevent breeding.

It is important to note that the Thoroughbred industry does not allow foals from surrogate mothers to be registered.