Settling Down: Reproductive Problems in Performance Mares

Let's say you've got a great performance mare you'd like to breed. But getting her in foal might not be as simple as swapping arena for breeding shed. Mares in performance careers can sometimes be hard to breed because these mares are under more stress than broodmares, and they might have hormonal problems that interfere with good conception rates.

Maiden Mare Syndrome

Pete Sheerin, DVM, Dipl. ACT, of Rood & Riddle Equine Hospital in Lexington, Ky., says a big problem he runs into is "maiden mare syndrome"--problems with the cervix. "Most of the performance horses we deal with are seven or eight years old before the owner wants to breed them; some of the warmbloods are in their teens," says Sheerin. "In many of these mares, the cervix doesn't relax like it should. They have a long, tight cervix, even when in heat. This causes several problems.

"If the mare is being bred live cover, the number of sperm that can enter the uterus is limited," he explains. "In some cases, the sperm can't get into the uterus at all. If a mare is bred by AI or even if the cervix is relaxed enough for sperm to get in, the other problem is that these mares tend to accumulate fluid in the uterus, which also interferes with conception."

It's wise to have a thorough breeding soundness exam done before trying to breed any mare, even if she's never had any foals. The exam enables the veterinarian to detect problems such as cervical abnormalities.

"There is no 'silver bullet' that works to get these mares pregnant," continues Sheerin. "With some, you put lots of work into them and still can't get them pregnant, and others do very well. Treatments to increase cervical relaxation may include Estrumate (synthetic prostaglandin) while they are in heat. This seems to help the cervix relax. We may also use misoprostal, which is prostaglandin E applied directly to the cervix. It's a drug used in humans for cervical relaxation. We do this to get the cervix relaxed enough to get sperm in and to get fluid out."

If the mare accumulates fluid, she is treated with uterine lavage, oxytocin (to stimulate uterine contractions), and other treatments. Thus the fluid can be cleared out before the embryo gets down through the oviduct and enters the uterus five to six days after breeding.

"Sometimes, in maiden mares, we find fluid in the uterus even before they are bred," explains Sheerin. "When a mare comes in heat, she produces fluid. This is a normal situation; the fluid helps clear debris, bacteria, and excess sperm from the uterus after breeding. In older maiden mares, however, because the cervix doesn't relax like it should, fluid can't get out and accumulates. This irritates the lining of the uterus, and what the uterus does in response to irritation is to produce more fluid."

Starting at about seven years of age, a mare that has never had a foal might start to have some of these problems. She's not really "old," but she is past the optimum time to start having foals.

"A lot of these mares, once they have a foal, no longer have the cervical problem," he adds. "The cervix had to relax and stretch to pass the foal through, and this seems to correct things so that next time it's more relaxed."

Hormone Problems

Performance mares might have problems conceiving related to their stressful athletic careers, or any hormone treatments they've been given to keep them out of heat. It depends partly on how much time elapses between when they stop work and when you try to breed them.

M.C. Baker, DVM, of Alpha Equine Hospital in Weatherford, Texas, works with cutting, reining, and show mares. Some of their breeding challenges revolve around the fact that many owners try to get embryo transfer (ET) foals during a mare's performance career, with no break for the breeding.

"They've been put on Regumate or other hormonal therapies to keep them out of heat, and some of these mares don't cycle well," says Baker. How long it takes a mare to start cycling normally again depends on the time of year she's taken off the drugs, and the drug that was given. If she's taken off the hormone in February or March, it might take several heat cycles before she'll breed well, he explains.

"The Regumate probably isn't as big a problem as some of the other drugs," Baker continues. "Some people use cattle implants in mares to keep them out of heat. There haven't been any scientific trials on how well that works or what it does to the mare long-term."

Sheerin says, "In performance mares that are still working--mares from which we're trying to get embryos--the first cycle after they come off Regumate is not a very productive one for embryo recovery or embryo viability. These mares need at least one cycle to get things going properly before you breed them. The uterus needs to be exposed to estrogen and then progesterone again, and relax and contract and do all the things it needs to do--things that it hasn't been able to do because it's been under the influence of Regumate or some other method to keep the mare out of heat.

"It's possible to get these mares pregnant and get embryos from them, but it's more challenging," continues Sheerin. "My practice, before I came to Rood & Riddle, was in Pennsylvania. We did a lot of Standardbred work, and a lot of embryo transfers on race mares in training. Our success was pretty good. But a big factor for success in these situations is the veterinary input regarding reproduction. These mares are at the track, and it's not as easy to have a reproductive person look at them, versus the track vet. The vets at the track are great with joints and athletic injuries, but it's not their specialty to rectally check mares."

If a mare needs extra work to get her cycling properly, or to resolve a reproductive problem, you need a veterinarian who specializes in reproduction.

Scheduling Problems

You also have to deal with timing problems of getting her bred while she's still competing--the issue of having the mare available at the same time the stallion is available to get the semen. Many people breed young performance mares to young performance stallions, says Baker. Having them both available at the same time can be a challenge, as you juggle the schedule of her cycle between major show events. Breeding (and flushing her about a week later) has to fit in with her next event. It has to be well planned to get it to work properly, and you need to allow enough time to resolve a possible problem before you actually breed her.

Sheerin says, "If your mare needs to be bred on a weekend and the stallion is away at a show, this is a problem. The stallion owner may have frozen semen available, but if your mare is still in training or has to show, the time and effort that's increased with the use of frozen semen may not make this feasible either--and it might not be a good gamble. It partly depends on how fertile the stallion is, but you also don't know how fertile your mare is if this is the first time you've tried to breed her."

Extra Challenges with ET

The important thing for a mare owner considering ET is to sit down and do the homework; look at all the options and factors that might be involved so there are no surprises.

"If you are doing embryo transfer, for instance, the mare must be checked every day to see when she ovulates, so you can do the flush at the proper time afterward," says Sheerin.

Baker explains that it may take seven to 10 days to get the mare to start cycling, even when using prostaglandin. "Then it takes another four or five days to get her to ovulate. If it's an ET mare, it's another seven to eight days (after breeding) before we can flush the embryo. We may not be able to keep the mares at the breeding farm for three to four weeks; the owner wants to be showing. We realize mares need a show record to make their foals valuable, but this makes it hard to schedule the breeding and embryo collection."

Many mares are shown until age five or six. Most cutters and reiners retire at seven, but the owner wants foals before then.

"An owner may bring us a 2-year-old, wanting a few embryo transfers before she goes into hard training," says Baker. "We've also had people bring a mare in the morning to breed, then show her in the afternoon, then bring her back the next day to see if she ovulated. After the event is over, she may be brought back to flush an embryo. Everyone expects to get a healthy, viable embryo every time we flush a mare, but with all that stress, this may not happen."

The ET process itself can damage the mare's reproductive abilities. "We have to ask ourselves how much harm we are doing to the uterus by trying to do so many embryo transfers," questions Baker. "By the time the mare is actually retiring from her career to become a broodmare, you may have used her up. She is still producing eggs and ovulating, but her uterine health is not as good. She becomes infected more easily and may have developed considerable scarring in the reproductive tract."

Fit Mares Might Not Cycle

Some mares in strenuous athletic careers don't cycle when they are very fit. "There's not much you can do for them," says Sheerin. "This is like amenorrhea (absence of menstrual cycles) in women who are very athletic, such as marathon runners. They don't start to cycle until their percentage of body fat increases and they essentially let down. A mare with this problem needs time off from work." How much time depends on the mare--how hard she's working, how stressed she is, what her body condition is (fat percentage), etc.

The female, horse or human, is programmed by nature to have a certain amount of body fat for optimum fertility and reproductive ability. In very fit young women, puberty comes later in life, and some don't ovulate regularly once they do start. The same is true with young mares. Part of this is due to cortisol release from the stress of extreme physical activity.

"You need to schedule breeding when the show or race season is slowest--with the mare not working as hard," explains Sheerin. "With Standardbreds, they let the mares down for a period of time, and try to do it during breeding season. Letting a horse down is the process of acclimating that horse to a non-race or non-performing environment. You can't just take a racehorse and put it out on pasture. It needs to adjust to a change in routine and feed."

If mares need a month or six weeks to let down before breeding, they can do it during breeding season and hopefully get an embryo or two while recuperating from work, or not working so hard.

Season of the Year

"I had a performance mare recently that suffered a tendon injury and the owner wanted to breed her since she needed a year off to heal," says Sheerin. "But it was October, and she didn't settle. We'll put her under lights and try her again in the spring. This must also be considered; are you trying to breed a mare during the normal breeding season (March through July) or outside of that--which might make it harder."


Stress factors when a horse is working hard can interfere with reproduction; sometimes the mare needs time to get over these stresses. "There is much we still don't know about stress in horses," notes Sheerin. "Is being in a different barn stressful? Is doing the work stressful? For some horses it is, and for some it isn't, but you can't tell from outward appearances whether the horse is stressed. Stress may be a factor you're not aware of until you breed a mare and fail to get an embryo or a pregnancy."

Baker says if a breeding farm gets 60-70% of mares pregnant per heat cycle, they've done a good job. "Through three heat cycles, this puts them up to a 90-plus percent pregnancy rate. But mares under a lot of stress, especially ET mares, don't fit into that 60-70% category. The percentage goes down when you try to get an embryo out of a show mare, and the ET protocol has a lower percentage as well; not every embryo you transfer will work. So on show mares, you lower the percentage considerably.

"Mares left on the farm to breed as broodmares rather than show mares have less stress and higher conception rates than mares being hauled in and out," Baker continues. "Shipped semen breedings of mares at home have higher percent pregnancies than in mares that are showing at the same time we're trying to get them in foal," says Baker.

The 2- and 3-year-old mares are being trained hard in preparation for cutting or reining futurities, he explains. Muscle breakdown metabolites and many other things can affect fertility. In a horse or human under great stress, reproduction shuts down.


Some treatments given to try to keep horses sound during athletic careers can affect reproduction. "As far as we know, Adequan and Legend (joint injections or supplements) don't have a detrimental effect," says Sheerin. "The cortisone-type injections might possibly have an effect, but we're not sure. It might depend on how long the drug is released. The different drugs put into the joints last for varying periods of time, but it's a relatively short period of time. When put in the joint, does it go systemically (throughout the body, rather than staying in the joint)?"

What might be more detrimental is intramuscular injection of dexamethasone to combat soreness or swelling and inflammation. The length of time a drug is in the system and what effect it has on fertility are still big unknowns, according to Sheerin.

Baker feels the long-acting steroids in joint injections seem to have some effect on fertility--on a mare's cycling, as well as how viable a flushed embryo might be. Stressed bodies produce cortisol, which can harm reproductive performance, and cortisone-type drugs produce a similar effect. While research is being done in this area to evaluate any effect of corticosteroid joint injections during pregnancy, it is very doubtful there is any effect because these steroids are administered in minute amounts.

Take-Home Message

Sheerin says, "The important thing for mare owners to realize is that it may be a little more difficult to get a pregnancy in a performance mare than in a typical broodmare. If they go into it with their eyes open, knowing it may take more time, effort, and money, and allow the extra time, that's one thing. But if they go into this expecting she should easily become pregnant just because she's a maiden mare, they may be disappointed."

STALLION FERTILITY: Overbooked Stallions

"Take care to pick a fertile stallion," says Pete Sheerin, DVM, Dipl. ACT, at Rood & Riddle Equine Hospital in Lexington, Ky. "The most popular stallions aren't always the most fertile. If mare owners do their homework and find out how fertile the horse is, this may make the process more successful."

M.C. Baker, DVM, of Alpha Equine Hospital in Weatherford, Texas, says that since the Quarter Horse association began allowing multiple registered foals from a mare during a year, many mares are sent to a number of different stallions for those embryo babies. "This is an unfortunate situation in the cutting industry. Many of the popular stallions are overbooked and may not settle all their mares. The stallion could easily handle 80 or 90 mares, but people are booking 125 mares or more, and 60 to 70 of those might be embryo transfer mares." Many ET mares get pregnant, are flushed so recipients can carry those foals, and rebred to carry their own foals.

When people try to breed mares to several different stallions during the year, this adds more of a challenge to actually trying to find a fertile stallion and making the embryo transfers work, says Baker.--Heather Smith Thomas

About the Author

Heather Smith Thomas

Heather Smith Thomas ranches with her husband near Salmon, Idaho, raising cattle and a few horses. She has a B.A. in English and history from University of Puget Sound (1966). She has raised and trained horses for 50 years, and has been writing freelance articles and books nearly that long, publishing 20 books and more than 9,000 articles for horse and livestock publications. Some of her books include Understanding Equine Hoof Care, The Horse Conformation Handbook, Care and Management of Horses, Storey's Guide to Raising Horses and Storey's Guide to Training Horses. Besides having her own blog,, she writes a biweekly blog at that comes out on Tuesdays.

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