Almost as important as a mare having a foal is mating her to have next year’s baby.
Foal heat breeding is an old management strategy to do just that. This is the first heat cycle a mare goes through after foaling and the first opportunity for a handler to mate her.
This usually happens six to 12 days after foaling. Mares can ovulate as early as seven days and as late as two weeks after foaling.
“From my perspective, deciding to breed in foal heat is not a yes or no. It’s a multi-faceted answer,” said equine veterinarian Dr John Knowles, DVM.
The benefits of breeding foals in heat center around maximizing a mare’s breeding opportunities. It is about taking advantage of all possible cycles of a breeding season. Or even increase the chances of reproducing this season if she loses a pregnancy.
This also prevents a mare from “sliding” towards ever later foaling dates, due to her 11 month gestation. It could get to the point where she will miss a year, foaling too late to be bred.
“Because gestation lasts 333 to 345 days, mares must become pregnant within a month of foaling to produce foals at 12-month intervals,” Knowles said. “Sometimes if you don’t breed them in foal heat, you don’t breed them that year.”
Historically, arguments against breeding foals in heat have focused on low conception rates.
“There is controversy regarding the relative fertility achieved by breeding the early post-foaling mare,” Knowles said. “There is often a lower pregnancy for mares bred in foal heat compared to mares bred in later periods of estrus.”
However, with proper mare management, the risks associated with raising foals in heat approach any other cycle.
Many things happen physically in the post foaling mare. “If a mare has had foaling issues, that’s a reason not to breed in foal heat,” Knowles said. “It’s probably wiser to give him time to recover.”
The more gradually the uterus returns to normal, the better the chances of successful breeding in foal heat.
The longer a mare takes to ovulate in foal heat, the more likely she is to be pregnant during that cycle.
“When a mare has been ovulating for 10 days, and her uterus looks good, we will breed in foal heat,” Knowles said.
The way mares are housed could also have an effect. “Exercise on pasture promotes uterine involution and expulsion of fluids, which could promote better foal fertility,” Knowles said.
Age is another consideration. Mares under 10 to 12 years old are more likely to get pregnant in foal heat and less likely to lose that pregnancy. The reverse is true for mares over eighteen.
Stallion fertility is also a consideration. “If I’m dealing with sperm of questionable fertility, I’d skip foal heat,” Knowles said.
Cost is another consideration with shipped semen. Some people only have one semen shipment with stud fees. “I don’t like to spend their money with a ‘Let’s just try to do colt heat’ attitude,” Knowles said.
It is not uncommon to see mares that will not have foaling heat, but they will have 30 days post-foaling heat.
“Most mares revert to normal 21-day cycles after foal heat,” Knowles said. “But some mares have an anestrous period after foal heat, if they are foaled early when the days are even shorter.”
It may help to put them under lights to lengthen the days during the winter months before foaling. The same is done with the open mares to get them to cycle earlier in the year.
The “short cycle” is another option on foal heat. It’s waiting for the mare to ovulate and timing the administration of prostaglandins correctly to bring her back into heat sooner.
“If you short-cycle a mare in foal heat, you only lose about a week or 10 days,” Knowles said. “It depends on the owner of the mare and may depend on where you are in the breeding season.
“If it’s February why not shorten it and avoid the colt heat,” Knowles continued. “But if you’re under pressure because she foaled late in the year, you might need those 10 days.”
Either way, close management of the mare is crucial to the breeding success of foals in heat. As long as the variables line up correctly, there’s no reason to avoid the foal-heat cycle as a general rule.
“If the young mare’s uterus is healthy, you can probably expect good fertility on a foal in heat,” Knowles concluded.