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The romantic view of horses mating conjures up a stallion running free with his herd of mares. Reality is usually different. Horses are expensive, and modern breeding is not left to chance. Most horse matings are carefully timed and involve veterinarians and handlers. A successful mating results in a healthy foal born after an eleven month gestation.
The Estrous Cycle
While the estrous cycle varies between mares, the average cycle is approximately 21 days. In three to five of those days the mare is capable of getting pregnant. She's most likely to conceive on the actual day of ovulation, which your vet can determine either by hand-palpation of her ovaries or via ultrasound. Your vet can inject hormones into a mare to cause ovulation. Signs of mares in heat or strong estrus include frequent urination, distraction and extra sensitivity. Breeding farms use "teaser" stallions to determine a mare's receptivity. These stallions, which might be ponies, don't actually breed the mare. The way the mare reacts to the teaser when he shows interest in breeding -- generally over the fence, not in the same paddock -- lets farm managers know whether or not she's reached the point in her cycle where she's ready for mating.
Pasture breeding is the most natural form, as it consists of turning a stallion out in a field with the mares you'd like him to impregnate. The horses breed when they feel like it, developing a herd structure along the way. The regular mating promotes the chances of a mare getting in foal. However, it's rare that high-value stallions are used for breeding in this manner, as the risk of injury increases considerably. Mares who aren't interested in breeding can severely injure a stallion.
Hand breeding is forced or facilitated "natural cover," the term for the natural way horses have always bred. However, the hands involved belong to the people controlling the mare and stallion. At many stud farms, hand breeding takes place in a special breeding shed. When an experienced stallion is brought to the shed, he knows what he's supposed to do.
Today, many stallions and mares never see each other during the mating process, because the entire operation takes place through artificial insemination. While A.I. is quite common -- except in thoroughbreds, as the Jockey Club permits only natural-cover insemination -- the use of embryo transfers from valuable mares into surrogate mares is gaining ground. This allows breeders to keep a mare in competition or save her from any pregnancy complications. For A.I. to be successful, you must work with your veterinarian to coordinate the insemination with fresh or frozen semen within 24 hours of the mare's ovulation.
- University of Missouri Extension: Horse Breeding Arithmetic: 2 + 2 = 1
- Louisiana State University School of Veterinary Medicine: The Normal Equine Estrous Cycle
- Equine Medical Service: So, You Want to Breed That Mare
- Pet Care GT: Horse Mating
- American Association of Equine Practitioners: Using New Reproductive Technologies in Your Breeding Program
- Comstock/Stockbyte/Getty Images