Horse Breeding on Foal Heat

Everyone involved with rebreeding mares wants one thing: to get her back in foal quickly. It’s good for the mare’s owner’s pocketbook; it’s good for the stallion owner’s breeding season to-do list; and it’s better for the mare – the sooner she and her at-side foal can head back to the pasture and enjoy uninterrupted quality time together, the better. Breeding on foal heat is an old management strategy aimed at doing just that.

Simply put, foal heat is the first heat cycle a mare goes through after foaling and a manager’s first opportunity to breed her. It typically occurs six to 12 days after foaling. Mares can ovulate as early as seven days and as late as two weeks post-foaling. But most mare managers would agree with Dr. John Knowles, resident veterinarian at Broadview University's Layton, Utah campus: “From my standpoint, deciding to breed on foal heat is not a yes or no thing, it’s a multifaceted answer.”

Why and Why Not

The advantages of foal-heat breeding center on optimizing opportunities for getting a mare rebred. It centers on taking advantage of every possible cycle in a breeding season, or even increasing your chances of breeding again that season should she lose a pregnancy.

And it helps avoid a mare’s “slide” to later and later foaling dates, due to her 11-month gestation, eventually getting to the point where she will miss a year, foaling too late in the season to be bred back. Depending on the mare, it could be every four to six years. “Because their average gestation is 333-345 days, mares must become pregnant within one month post-foaling to continue producing foals at 12-month intervals,” points out Dr. Terry Blanchard, a veterinarian and professor at Texas A&M University College of Veterinary Medicine & Biomedical Sciences.

The importance of these advantages depends on how critical it is for your mare to annually produce a potentially profitable foal, or how important foals with early foaling dates are in your industry. The mare herself could have a say on its importance. “I have managed mares with a history that if you don’t get them bred on foal heat, you don’t get them bred that year,” says Dr. Knowles, although he stresses that is not the norm. Or it might be necessary to breed on foal heat to meet a stallion’s availability window, especially if the horse is on a competition schedule.

Historically, the arguments against breeding on foal heat have centered on poor conception rates. “Controversy exists regarding relative fertility achieved by breeding the early post-foaling mare,” Dr. Blanchard says. “Studies have shown in general, a lower pregnancy rate is often achieved for mares bred on foal heat as compared to mares bred on later postpartum estrous periods.”

“It used to be that veterinarians would always try to talk you out of breeding on foal heat,” says Laura Wipf, co-owner and operator of the Royal Vista Ranches breeding facility in Wayne, Oklahoma, “and it was because of conception rates lower than 50 percent.”

But that’s not the case anymore, she points out, given improved management practices in using ultrasound to closely monitor the mare’s uterus and recovery post foaling, the status of the mare’s follicles and other health factors. With the right mare management, the risks associated with foal-heat breeding approach any other cycle. Dr. Blanchard points to studies that “reported that pregnancy rates achieved on foal-heat breeding were farm dependent.” “I managed a stallion for a man who had 30 mares of his own that he bred,” Dr. Knowles says. “He wanted to breed every mare we could on foal heat, and we had 90 percent conception rates for his program on foal-heat breeding.”

Setting Up For Success

Several factors go into making the decision whether or not to breed a mare on foal heat, and the mare’s post-foaling physical health is primary. A lot is going on in the post-foaling mare physically: The uterus sloughs placental debris; the endometrium, or inner lining of the uterus, is restored; and the uterus “involutes” or decreases in size. In that first week, there’s a lot of inflammation in the uterus, and bacteria might be present. If the uterus doesn’t involute normally, that’s an opportunity for fluid to accumulate. “If a mare has had any kind of problem foaling, such as dystocia, red bag or retained placenta, that would be a reason in my mind not to breed her on foal heat,” Dr. Knowles says. “It’s probably wiser to give her time to recover.”

The more progressively the uterus returns to normal, the better the chances for foal-heat breeding success. Dr. Knowles says, “If a mare comes into heat quickly, say five days post foaling, and it looks like she’s going to ovulate before 10 days post foaling, I don’t like to breed her on foal heat.” Studies have shown that the longer the mare takes to ovulate on her foal heat, the higher the chance she’ll get in foal if bred on that cycle, and veterinarians believe it could be linked to the longer amount of time the uterus has to involute. Laura agrees: “For us on the farm, provided that the mare looks like she’ll go out far enough, ovulating past 10 days, and her uterus looks good with no fluid, we’ll breed foal heat if there’s no other reason not to.”

How mares are housed could have an effect, too, Dr. Blanchard says. “It is possible that the exercise associated with being maintained on large pastures promotes more rapid uterine involution and fluid expulsion, which could favor enhanced foal-heat fertility,” he says.

Age is another consideration. Dr. Blanchard points out that mares younger than 10 or 13 are more likely to become pregnant on foal heat and less likely to lose that pregnancy; the converse is true for mares older than 18. Both Laura and Dr. Knowles stress the importance of using a fertile stallion, too, especially with frozen or cooled shipped semen.

“If I am dealing with semen of questionable fertility, I would skip the foal heat,” Dr. Knowles says. “The cost is another consideration with shipped semen,” he adds. “Depending on the contract, some people have just one shipment of semen with the stud fee, or they can be charged anywhere from $250 to $700 to collect and ship, in addition to my costs. I don’t like to spend their money with a ‘Let’s just try foal heat’ attitude.” When dealing with cooled shipped semen and foal-heat mares, Laura points out the importance of the stallion manager having confidence in mare management on the receiving end. “You try to push your foal-heat mares out as far as they will go to increase your odds for them to ovulate and conceive,” she says. “When someone is ordering semen for a foal-heat mare, it matters a lot to me to have confidence in who’s managing that mare, especially if he’s a high-demand stallion.”

Additional Strategies

Laura says it’s not uncommon to see mares that won’t have a foal heat, but they will have a 30-day post-foaling heat – she tends to see that in mares that foal early. “We start all of our early foaling mares under lights,” she says, “for that reason.”

Most mares return to normal 21-day cycles after the foal heat, but some mares might have an anestrous period after the foal heat, especially if they foal very early in the year when the days are still shorter. It can help to put them under lights and lengthen their days in the winter months prior to foaling, just as you do open mares to get them to cycle earlier in the year.

“Short-cycling” is another option on the foal heat – waiting until the mare ovulates and properly timing prostaglandin (Prostin, Lutalyse, etc.) administration to bring her back into heat sooner. “If you short-cycle a mare on foal heat, you don’t lose but about a week or 10 days, ideally,” Laura says. “Again, it’s up to the mare owner, and it can depend on where you are in the breeding season. If it’s February, why not short cycle her and skip foal heat; but if you are under the gun because she’s foaled late in the year, you might need those 10 days.”

Regardless, close mare management is crucial for foal-heat breeding success. As long as the variables line up right, there’s no reason to avoid the foal-heat cycle as a rule. Dr. Blanchard sums it up: “Bottom line – if the mare’s uterus is involuting well, there’s no uterine fluid and you are dealing with a young mare – then you can probably expect good fertility on a foal-heat breeding.”