Mare is a Four Letter Word

Dr. Kimberly Brokaw, DVM

(6/2014) A couple of years ago I attended a lecture at the American Association of Equine Practitioners Convention titled Mare is a Four Letter Word. The lecture focused on the difficulties of getting mares pregnant and managing them throughout the pregnancies. This weekend has left me in complete agreement with the lecture presenter.

Last year one of my clients had three mares that were notoriously difficult to get pregnant. The one hadn't been pregnant in five years. Because of previous years' difficulties we elected to start the breeding process at the end of March. While for thoroughbreds this would be late in the year, these are warmblood sport horses. A mare's pregnancy typically lasts 11 months. As sport horse people want their mares to foal out in May, we tend not to start the breeding process in March, except in difficult situations such as low fertility.

Sport horses, unlike Thoroughbreds also tend to be bred through artificial insemination. Artificial insemination has numerous benefits. First it eliminates the risk of injury due to fighting between the mare and the stallion. Risk of disease transmission also decreases. AI permits both mare and stallion to be on opposite ends of the country as well as for them to continue to compete during breeding season. One of the down sides to AI is that some of the sperm die during the shipping process and you also have to coordinate sperm delivery to when the mare is going to ovulate. All of this as well as other factors can result in lower conception rates. In this situation we assumed that the mares would not get pregnant on the first breeding attempt, and would require repeated inseminations to conceive.

We were wrong. All three mares got pregnant on the first try. While the owner was initially ecstatic, as it came time to sit in the barn at night and monitor the mares for signs of foaling during the frigid February nights, the owner was less happy. Having the owner or other foaling attendant present at each foaling is essential to maximizing the chance of the foal surviving. Situations such as foals who are unable to break the amniotic sac, require rapid human intervention. Therefore, sport horse breeders expect to sit up night after night to make sure they will be present for the foalings.

Since most sport horse foals are born in the spring, the sport horse breeders don't expect to sit outside in a 15 degree barn for one February night after another after another. Each of these mares foaled during different nights of the polar vortex. The owner managed to be present for each foaling. She used heat lamps to warm herself and the foals, and the foals did great. The owner looked rather cold and worn by the third foaling. This year the owner said that there was no way she was ever going to even contemplate breeding a mare before May.

As the month of May progressed, the owner continued to monitor the mares for signs of coming into season. She started noticing signs the week before Memorial Day. Not only did this client notice her mare coming in, but so did another one of my warmblood clients. While this may not at first seem significant, it is in fact extremely significant when doing AI. Not only will FedEx not deliver semen on Sundays, but they won't deliver on holidays either. Stallion owners also usually only have certain days when they collect semen (i.e. Monday, Wednesday, Friday). The presence of the holiday meant that the mares had to either be ready to breed by Saturday, or not ready to breed until the Thursday following Memorial Day.

As I was ultrasounding the mares and contemplating which days I'd be able to obtain semen, my mind wandered back to the lecture "Mare is a four letter word." The lecturer was correct. It seemed like these mares were going to be ready to breed Sunday night/Monday morning. While the lecturer went into several mare fertility issues, he also spent time covering options when the mare is going to ovulate on weekends, holidays, and other times when it was impossible to get semen delivered. The vet has a couple of options. Based on the size of the follicle the vet can give an injection of a medication that will make the mare ovulate. If the mare is far enough along in her cycle, that becomes a very good option. If the mare isn't far enough along, there are also medications to try and slow down the development of the ovulatory follicle so that they don't ovulate until after the holiday. While it sounds like with those medications, weekends and holidays would not be problems, they still are. Mares don't always respond to the medications the way the vet wants them to and pregnancy may not result. When a mare doesn't conceive by June, most likely the breeding year is lost. Therefore, breeders are usually very eager to avoid losing an ovulation cycle because of a holiday like Memorial Day.

Two of the mares were close to ovulation. We gave an injection to stimulate ovulation and fortunately were able to breed them before the holiday weekend. The other mare was given a medication to delay ovulation. As I am writing this article, I still don't know if I was successful in delaying ovulation. I will check the mare soon and plan the semen order based on the follicle size. Then, 14 days after inseminating the mares, I will ultrasound them again to see if they are pregnant.

To those who are not breeders, mares and foals, grazing out in the fields, conjure up images of peace, tranquility, and no stress. These images are very far from the reality of breeding. Breeding is full of major catastrophes and little stresses. It is the little stresses in breeding mares, such as coordinating semen delivery around a holiday that remind me of how much time and effort owners put into their brood mares, and that I don't want to own one.

Read other articles by Dr. Kim Brokaw