When She Doesn’t Take

There are many reasons why a mare fails to get pregnant or carry a foal to term, and knowing how to identify them can help.

One of the biggest disappointments for the horse breeder is to discover that a bred mare is not pregnant. There are many reasons for reproductive failure. The horseman and veterinarian must work together to try to determine what happened and how to correct the problem, if possible.

Keeping Track

According to Ahmed Tibary, DMV, PhD, dip.ACT (associate professor, Large Animal Theriogenolgy, Washington State University), one of the biggest responsibilities of the horse breeder is keeping thorough records on mares. It’s very difficult to know what’s been happening with a mare if she was merely turned out to pasture with a stallion, for instance. It’s easier to track down a problem if there was first a breeding soundness examination, a breeding date, a record of how many times the mare was bred, whether by live cover, artificial insemination, shipped or frozen semen, etc. It helps to know the quality of the semen. Are there records on other mares that were bred to that stallion or using his semen? If shipped semen was used, was it properly prepared and handled?

“Today there are many things that can go wrong. A lot of semen is being shipped and there is not always a good way to know how it is being handled or whether it’s contaminated,” says Tibary. This can add to the risk for a mare not settling.

If the stallion is fertile and any problems with the semen are ruled out, the next step is to find out if there’s a problem with the mare. Are we dealing with a mare that is not getting pregnant at all, or a mare that is getting pregnant and losing it? If you don’t have good records, it can be harder to figure this out.

“No matter what the complaint is, the first step is looking at the mare’s general health, looking at her history and then doing a basic breeding soundness examination. If the history of the mare and her physical examination does not reveal anything that would explain why she is not pregnant, then we focus on the reproductive organs,” Tibary says. The process of diagnosing a fertility problem takes certain steps—to rule out or rule in various factors.

“We prefer to do an examination either early in the breeding season or as soon as the mare is found not to be pregnant. I generally recommend doing this with any mare that has been bred in a proper manner but has not settled or has lost the pregnancy after two cycles,” he explains. Those mares need to have at least a minimum breeding soundness exam.

“The examination also puts a mare into one of several large categories. The first category includes mares that have never had a foal before (maiden mare or an older mare with no history). With these mares any number of problems could be possible. The second category are mares we know have had at least one foal, but now are not getting pregnant. Again, the history establishes what’s happened between when she had the last foal and now. Was there any problem with the foaling, for instance?” he asks. Mares that have had a history of repeat pregnancy loss or abortion are handled in a different category.

The Exam

A breeding soundness examination includes a look at the conformation of the perineum and vulva, trans-rectal palpation and ultrasonography of the entire reproductive tract including uterus and ovaries, a vaginal exam to evaluate the vaginal cavity and cervix, and an endometrial culture and cytology, as well as a biopsy. “This gives you a minimum database to work from. If a mare is being bred and monitored by a veterinarian, you have lots more data on her cycle, ovulation, etc.,” explains Tibary. “Once we have that information, in about 80 percent of cases, this can lead us to classify the likelihoods or possibilities and we can start looking at some options,” he says. In some instances, endocrinological evaluation may be needed to see if there are hormonal problems.

What Went Wrong?

If you look at the causes why mares either don’t get pregnant or lose the pregnancy very early, there are two very major reasons (if you’ve already eliminated breeding management errors and semen quality). “First is a problem with uterine inflammation. Second is a problem with uterine integrity or health of the uterine tissue—particularly endometriosis or degenerative changes,” Tibary says. This can be common in an old mare even if she has never had a foabecause there are some changes that occur with aging. There are also changes that are age related but exacerbated by history of infections, etc.

One scenario seen frequently today is problems encountered with old maiden mares. Many horse professionals focus on the mare’s career first without giving her time out to have a foal. By the time they decide to breed her, she is past her reproductive prime and her fertility may be borderline. Those mares can present an interesting challenge.

The Older Mare

“Old maiden mare syndrome is characterized by a non-responsive cervix. The cervix is very tight and does not respond very well to hormones,” says Tibary. It does not relax and open normally during estrus. Therefore fluid tends to accumulate in the uterus during heat and also after insemination. Also, it may be difficult to get semen into the uterus. Excessive accumulation of fluid before insemination will hinder semen function and fertilization, while excessive accumulation of fluid after insemination and ovulation will compromise survival of the embryo.

With an older mare it may also be difficult for her to clear the uterus—to get the normal debris and dead semen products out of the uterus after she’s bred. Every mare has a reaction to breeding, since semen is a foreign substance to her body. There is some inflammation in the uterus for a short time. In a normal, healthy uterus, these products are flushed out in the first days after breeding, leaving a clean uterine environment by the time the fertilized egg moves out of the fallopian tube into the uterus. The older mare may have an inadequate uterine clearing mechanism and does not get rid of the debris and inflammation.

“The history and breeding exam give us some clues. From there, the approach to a problem mare will depend on what the diagnosis is, and also how to manage the infertility. We not only have to treat it, but also manage the mare afterward. Many people forget about the importance of management. If a mare is sensitive to uterine infection, we may treat the infection and clear it up, but the success of rebreeding her will depend a lot on how that mare is managed,” he explains.

It can be a challenge trying to breed her again without getting the uterus contaminated. She should be bred carefully and with minimum risk for contamination, breeding her only once rather than repeated times, for instance. “You also have to make sure she clears the uterus afterward. This is why we go through the process of promoting uterine contraction using oxytocin or even flushing the uterus after breeding, for instance,” Tibary says. These mares take more care and management than most young mares with a young, healthy uterus.

“This is one of the biggest advances in recent years in managing mares with infertility. Identifying these mares early and trying to not let them get into trouble after an AI breeding or natural cover can be a big help. You try to stay ahead of the game by getting the uterus cleaned up (dead sperm and inflammatory products removed) afterward,” he says. Conformation abnormalities need to be repaired prior to or immediately after breeding, along with flushing of the uterus after ovulation.

“The initial diagnosis of pregnancy should be done at 14 days, and then we go from there,” says Tibary. If an old mare has a lot of cysts in the uterine lining, these may sometimes interfere with proper attachment of the embryo. Cysts can be detected in the initial breeding soundness exam. These may not be a problem, but can sometimes compromise fertility. Usually if there are multiple cysts and the mare already has a history of not getting pregnant or of losing the pregnancy early, those cysts need to be removed.

After Fertilization

There are some very critical times during pregnancy when things can go wrong after initial fertilization of the egg. For example, “you want to make sure the embryo is able to dialogue with the uterus so the uterus does not reject it. This dialogue depends on free movement of the embryo in the first 17 days,” Tibary says.

Between about day 10 (when the embryo is floating freely in the uterus after coming out of the fallopian tube) and day 17, the healthy embryo moves a lot, in order to send a signal to the uterus that it’s in there. If anything impedes free movement of the embryo, this signal may not be sent. “Large uterine cysts or a big, heavy, baggy, flaccid uterus with no contraction may hinder the movement of the embryo. Inadequate levels of progesterone would also hinder this dialogue between embryo and uterus which is so important, to ensure that the uterus won’t attempt to start another heat cycle,” explains Tibary.

“The next step is implantation of the embryo (attaching itself to the uterine lining). This requires that the uterine surface be healthy. If the mare has sustained a lot of damage to the lining of the uterus (endometrium), then there is not enough healthy tissue for the growing placenta to enter and attach. This is a critical period, while the embryo and its placenta are establishing and anchoring to the uterine lining,” says Tibary.

Once the mare gets through this critical period successfully, breeders can breathe easier. In order to make the process as smooth as possible, good information upfront will help in the long run.






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