8 Steps for Breeding Your Mare

Take a systematic approach to managing your broodmare to have the best chance at a successful pregnancy

Sperm, meet ovum. If breeding horses were as simple as that, we wouldn’t have an entire branch of the veterinary profession devoted to equine reproduction. Even in-heat mares and virile stallions don’t always a foal make. And if your broodmare herd includes a collection of maiden, older, and/or subfertile mares, you have even more to think about and keep track of to ensure a successful breeding season. Taking a systematic, step-by-step approach to managing each mare, in partnership with your veterinary team, can help cultivate success next spring.

Step 1: Consider the mare’s overall health

Margo Macpherson, DVM, MS, Dipl. ACT, a professor of Large Animal Clinical Sciences at the University of Florida’s College of Veterinary Medicine, in Gainesville, says there’s no one recipe for broodmare management; veterinarians must assess each mare individually.

Before focusing on a mare’s reproductive health, owners must first note her overall wellness. Does she appear healthy? Are her hooves in good shape? What vaccinations are due? Does she need a fecal egg count to check for parasites? Is she carrying too much or too little weight? Does she need a dental exam? 

Karen Wolfsdorf, DVM, Dipl. ACT, a field veterinarian and reproductive specialist at Hagyard Equine Medical Institute’s McGee Fertility Center, in Lexington, Kentucky, says one of the most important initial observations she makes is the mare’s Henneke body condition score (BCS). Ideally, broodmares should score between a 5 and 7 on the 1-to-10 scale prior to breeding.

“I like to be able to feel ribs but not see ribs,” says Wolfsdorf.

She says she also looks for protruding fat pads, a cresty neck, or other abnormalities that might suggest the mare has pituitary pars intermedia dysfunction (PPID, or equine Cushing’s disease), insulin dysfunction, or some other systemic illness that could affect the reproductive system.

She also takes into account the mare’s breeding history, including issues getting pregnant, endometritis (inflammation of the uterine lining), or abortion.

If the breeding will be via live cover, it’s important to know the chosen breeding shed’s stipulations. For example, Wolfsdorf says some breeding sheds require certain vaccinations, such as for rhinopneumonitis (herpesvirus-1), which veterinarians usually administer three weeks to three months prior to breeding to prevent the stallion from potentially being exposed to the virus. Wolfsdorf says owners should know the mare’s vaccination history and keep her current on her vaccines against diseases in that region, including during pregnancy.

To reduce the risk of spontaneous abortion, the American Association of Equine Practitioners recommends vaccinating mares against herpesvirus-1 at five, seven, and nine months of gestation. On some high-traffic farms, veterinarians might administer the herpesvirus vaccine every two months, but this is off-label use.

8 Steps to Breeding Your Mare

Step 2: Schedule a breeding soundness examination and address any problems

Getting a mare pregnant is a team effort between the broodmare owner and the veterinarian, says Wolfsdorf. Veterinarians typically perform a breeding soundness exam—a reproductive exam for broodmares—to identify and manage possible problems before breeding.

When discussing these exams, Macpherson says she’s mindful of a client’s budget and lists all the options to equip him or her to make an educated decision on which evaluations to perform. Often, a mare might only need a breeding soundness exam if she does not conceive after the first two or three attempts.

“The breeding soundness evaluation is far more important for the mare with difficulty in getting pregnant or the aged or middle-aged maiden mare,” says Macpherson. “I really think that a breeding soundness evaluation is meant to problem-solve or to provide prognostic information, so that the owner can make informed decisions.”

For most broodmares that have not had any breeding-related issues, Wolfsdorf starts by examining the mare’s reproductive anatomy, including perineal conformation—which involves the vulvar lips, the vestibular-vaginal fold and/or the hymen, and the cervix. If a mare has poor perineal conformation, she is at risk for reproductive tract contamination with feces, air, and microbes. To prevent this and possible resulting infection, veterinarians can suture the vulvar lips together (a procedure called a Caslicks), later removing the stitches for breeding and foaling.

An exam will also include transrectal palpation and an ultrasound examination. These tools help determine the stage of the mare’s estrous cycle. They can also allow the vet to verify the size and functionality of her ovaries and identify potential abnormalities within the uterus and vagina, such as excessive fluid, which can be a sign of inflammation or poor uterine clearance.

Macpherson says she performs an ultrasound exam every time she evaluates a mare prior to breeding. “I think the tools of palpation are extraordinarily important, but there’s so much that we can see with an ultrasound that makes an impact on breeding management,” she says.

Palpation and ultrasound examination results often determine the next steps in abnormal cases, says Wolfsdorf. “What we see in her uterus will dictate what type of culture and cytology we may want to do,” to confirm and identify pathogens, she says. 

She says she most commonly performs this in mares that have a “baggy, saggy” uterus, such as older broodmares, those that have had multiple foals, or ones with a history of endometritis, to look for inflammation and infection. These mares might also be more prone to breeding-­induced endometritis because of impaired uterine clearance.

An endometrial biopsy adds another piece of information to the evaluation. With this procedure the veterinarian evaluates a piece of the endometrium microscopically to look for abnormalities, such as inflammation, scar tissue around glands and vessels, and dilated lymphatics. Evaluating endometrial tissue can help the vet predict the probability of a mare becoming pregnant and maintaining the pregnancy to term.

If a veterinarian needs further information on a mare, he or she can perform a hysterocopic exam, which involves inserting an endoscope into the uterus to look for abnormalities such as foreign bodies, adhesions, or fungal/bacterial plaques.

The information gathered during the breeding soundness exam can guide your veterinarian to recommend certain management techniques or treatments before breeding.

The Horse December 2019​This article continues in the December 2019 issue of The Horse: Your Guide to Equine Health Care. Subscribe now and get an immediate download of this issueincluding this in-depth feature on taking a systematic approach to managing your broodmare to have the best chance at a successful pregnancy.

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