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Mares and Breeding Considerations


By Leigh Ballard

The ideal mare used for breeding should be attractive, of good conformation, possess a sweet temperament, and be of such bloodlines or abilities that it can be reasonably assumed that her favorable characteristics and performance abilities will be passed to the offspring. The ideal mare owner should not breed the mare simply to put another horse in the world, but to make a positive contribution to the horse industry. The owner will have thought about Dr. Whitaker’s “Seven Ps of Breeding” (see January 2012 MSHR) and will have a responsible plan for a positive outcome. 

It is advisable to manage a mare’s health prior to breeding for optimal breeding success. Many owners vaccinate their horses in spring, and ideally, vaccinations should be up to date for the maiden mare (a mare who has never foaled) before breeding. Mares currently in a breeding program should already be on the appropriate vaccination schedule (as recommended by the American Association of Equine Practitioners, AAEP). A de-worming program should be in place. Body condition score should be a 6 or higher, on the fleshy side but not obese. Studies have shown that conception rates are better for mares with a body score of 7. The mare’s overall health should be good with no indication of illness or infection as she heads to the breeding barn.

A mare that does not meet these health considerations may pose problems with fertility. Uterine infections (endometritis) can be a reason for infertility. Dr. Colin Anderson, attending veterinarian at Masterson Farms in Somerville, TN, says, “As a general rule, for established broodmares with no known problems, a uterine culture and accompanying cytology are not necessary. However, a mare that may require these tests would be one with conformational issues such as a vulva which tilts upwards, which can catch fecal material that would cause her to be prone to infection. Also, a mare who did not have a foal this year, although she was bred and didn’t conceive or lost the pregnancy, would be another one to test. You would want to rule out endometritis as a reason for not having breeding success.”

Some artificial insemination (AI) breeding contracts require a uterine culture and cytology for the mare, primarily so that the stallion owner does not go to the expense of collecting and shipping semen to a mare who is not likely to conceive. If infection is present, it may need to be treated before the breeding process is started. All live cover breeding in the Thoroughbred industry and other top breeding barns requires these tests for the stallion’s protection.

Dr. Anderson says, “Most people have a price range in mind for what it will cost to breed their mare. Usually though, they base that price on one cycle - the stud fee and a few veterinary procedures and checkups.” Anderson says this may be wrong thinking, however. “Horses are not the best reproductive models,” he says, “even in the wild. A mare owner should have in mind that it may require several cycles and attempts before the mare conceives.”

With AI especially, the stud fee is only a part of cost considerations. Since timing is so critical for shipping of cooled semen, the mare’s heat cycle and projected time of ovulation is closely monitored with ultrasound exams, at a cost each. Up to four or five ultrasounds per breeding cycle are normal, and because of this, the mare might have to board at her veterinarian’s clinic. She might be induced to ovulate with hormone injections, at a cost each. When the semen is ordered, there are collection and shipping costs from the stallion’s barn. After the mare is bred, there are other treatments to help ensure a higher chance of conception.

Timing of breeding is another consideration. Anderson says, “Photoperiod, the length of daylight, is what drives a mare’s cycle. Horses are long-day breeders, so that means summer is their natural time. You will rarely see a foal born in January or February from natural breeding conditions around here. The closer you get to the equator, though, the more often that may occur naturally.”

Still, many breeders strive for early foals born in January and February.  Janné Stewart, Breeding Manager at Masterson Farms, says, “The early foals matter if a farm is showing, competing and selling young horses. Two-year-olds that were born early are generally going to have an edge over those that were born in May, and that matters with futurity horses. They will typically be bigger and more developed. But somewhere between the second and third year, they catch up to each other and they are all at about the same level by the time they are 3 to 4-year-olds.” She adds, “Unless showing is a serious consideration, breeding times more in line with the natural cycle are more likely to be more efficient for both cost and success.”
If the mare needs to be bred early, the photoperiod must be controlled. The mare needs light from 6 a.m. to 10 p.m. To achieve this, she must be stalled with artificial lights to extend the day. “She will need about 60 days light to start getting her cycles in January. This means you have to start thinking about lights as early as November. The rule of thumb for how much light is that if you can comfortably read a newspaper in all 4 corners of the stall, then the light is bright enough. Three corners are not enough; it has to be bright over the whole stall,” Stewart says. “On some large operations where stalling and lighting like this just isn’t practical because of the number of mares, they build large paddocks with stadium lights and run the mares in those to control the photoperiod. It costs on the front end, but it works when you have to control the breeding time on that many mares.”

Besides early breeding, another common practice is to breed on the “foal heat” or the first cycle after the foal is born, typically about 10 days post-partum. Many people think this is a fertile period, but Anderson disagrees. “High fertility on a foal heat is a myth. The conception rate on foal heat is only about 50-60%. Of course, there’s wide variation among individuals, but studies show that the most fertile time to breed a post-foaling mare is her second heat cycle, about 30 days post-partum. Also, a successful breeding then will give you a foal at the same time next year as this year. “
In the early stages of pregnancy, nutritional needs for pregnant mares are not very different from other horses. But, as a mare get closer to foaling, her exposure to fescue grass needs to be eliminated, and her energy requirements increase dramatically. In the last three months, the foal will double in size, so the mare will need to increase her intake by about 20% to allow for the foal’s growth. The first two months after foaling she will need almost double the calories she was taking in at the beginning of her pregnancy.

Finally, consideration should be given to the mare’s behavior.  Maiden mares, especially, need to start a handling program at least by the last three months of pregnancy.  Stewart foals out about 45 mares every spring. About 20% of these are maiden mares or mares from other farms whose behavior during foaling is an unknown factor. She says, “I start a gentling program well in advance of the delivery date. I want to make sure the mares are fully accustomed to being touched all over: teats, belly, tail, hind legs. I want them very accustomed to me. It is important that a mare have respect and trust in the person who is likely to be on hand at foaling. I want the mare to work with me and not fight me if there’s a problem. I want her to listen to me; the last thing I want is an uncooperative or panicked mare.”

“I use the Predict-a-foal tests to let me know when the baby is probably coming, and Foal Alert electronic monitors to notify me when it actually starts to be born, so I can be on hand with the mare to help her if necessary. Most babies are born just fine, but now and then they need some help. Also, being there at the birth with a cooperative mare lets me start imprinting the foal right away, besides attending to the umbilical cord and placenta.”

Health, costs, timing, nutrition and behavior are all important aspects of mare management for breeding. When these aspects are all given thoughtful consideration, chances for a good outcome for mares, foals, and owners are greatly increased!

Practices involved in foaling procedures and imprinting the foal will be discussed in the March 2012 issue of MSHR.

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