Photo: Anne M. Eberhardt

Making an informed decision to breed a mare is an exciting time in an owner's life. There are so many things to do: pick a stallion, prepare a foaling location, and dream big about the foal's potential, to name a few. But the first thing on the list should be to have a veterinarian perform a breeding soundness examination on the mare.

During a presentation at the 2012 Western Veterinary Conference, held Feb. 19-23 in Las Vegas, Nev., Walter Threlfall, DVM, MS, PhD, Dipl. ACT, a consulting theriogenologist (reproductive specialist) in Powell, Ohio, and professor emeritus in the Department of Veterinary Clinical Sciences at The Ohio State University's College of Veterinary Medicine, gave an in-depth look at what a mare's breeding soundness exam should entail.

"The purpose (of a breeding soundness exam) is to determine the probability of a mare conceiving and the cause(s) of sub- or infertility," said Threlfall, a Quarter Horse breeder for more than 30 years.

Obtain a History

Veterinarians should begin a breeding soundness examination by obtaining a detailed history of the mare, Threlfall said, indicating that much can be learned from this portion of the process.

In addition to learning about the mare's age, breed, feeding and housing situations, and general health, a veterinarian will also evaluate her vaccination and deworming status, Threlfall said. The latter part, he noted, can give the veterinarian additional clues about the owner and how he or she would care for the resulting foal. If the mare hasn't been dewormed or vaccinated recently, for example, he recommended seriously discussing the implications of breeding with the client, as a mare should be dewormed and vaccinated for not only her health, but also the foal's.

The veterinarian will also evaluate the mare's estrous pattern during the first portion of the examination. Threlfall noted it's very important for the owner to keep detailed records of the mare's heat cycles leading up to the examination.

When was the mare last bred and what method (natural cover or artificial insemination) was used? Threlfall said this information is crucial to best evaluate a mare's fertility or breeding potential. If the mare has been bred in the past, it's also useful to know the stallion's fertility. On a side note, he added, it's important to understand the difference between maiden and barren mares in a fertility examination. Maiden mares, he said, have never been bred (i.e., covered or inseminated) before, while barren mares have been bred before, regardless of whether breeding was a success or failure.

For mares that have been bred before, Threlfall said, the veterinarian will also evaluate her foaling history. Past foaling dates, past abortions (including dates and causes, if known), retained placenta and treatment thereof, and endometritis history (including the diagnosis, treatment, and biopsy results, if known) is useful information for a veterinarian to have during a soundness examination.

Physical Examination

Once the attending veterinarian has obtained the mare's detailed history, he or she will begin a physical examination. Different from a prepurchase examination, Threlfall said, all body systems should be evaluated with the understanding that the mare could be carrying a foal to term. The veterinarian should look closely to determine if problems could arise as a result of the mare's conformational or medical problems.

Threlfall stressed the importance of looking for undesirable genetic traits that the mare could pass on to a foal and educating the horse owner accordingly. For example, a mare that possessed angular limb deformities as a foal or has some other conformational traits could easily pass those issues on to a foal. Threlfall suggested making the owner aware of these potential issues, but relayed that a veterinarian should never tell an owner not to breed a mare for genetic reasons.

Palpation is the next step in a physical exam. While ultrasound examinations have come into play and some veterinarians turn to them before palpation, Threlfall recommended performing both--starting with palpation. "They both have a place," he said. "But palpation is part of the art of veterinary medicine and gives valuable information."

During a palpation the veterinarian will look for anything that's not normal in the uterus, ovaries, and cervix, Threlfall said, including uterine cysts, uterine fluid, poor uterine tone, cervical lacerations, or extreme ventral dilations. He also suggested veterinarians be comfortable palpating "normal" mares, as know what's "normal" makes identifying something "abnormal" much easier, he said: "(During a palpation) if you feel something you know is abnormal, there's probably something wrong. Don't just walk away and forget about it; find out what's wrong."

Next, Threlfall said the veterinarian should evaluate a "critically important but often overlooked" aspect of the mare's reproductive tract: vulvar conformation. The vulva should normally be in an upright position in a straight line with the anus. The vulva should be below the level of the floor of the pelvis, and the vulvar lips should meet evenly to form a seal. Poor vulvar conformation could lead to subfertility and could necessitate a Caslick's procedure (surgically closing the upper part of the vulva) to correct the abnormalities before breeding.

A digital cervical and vaginal examination is indicated during a breeding soundness exam, Threlfall said, as is endoscopy in some cases to visualize the endometrium (uterine lining).

Laboratory Evaluations

Finally, Threlfall discussed some laboratory evaluations designed to identify uterine infections.

Uterine Cultures--Uterine cultures look for the presence of bacteria in a mare's uterus. Although it remains a topic of discussion, Threlfall noted that uterine cultures can be performed when the mare is in heat or after she's come out of it. "The custom of culturing mares only when in heat originated from the time when all cultures were taken using a culture instrument through a speculum," he explained. "It does not make a difference."

One of the most common bacteria found on uterine culture, Threlfall said, is β-hemolytic Streptococcus, which causes about two-thirds of all uterine infections. Other common organisms include Klebsiella sp., Pseudomonas sp., Proteus sp., and Corynebacterium spp. Contaminants commonly found in the uterus that don't necessarily cause infections include Escherichia coli, Staphylococcus sp., and Bacillus sp. These organisms usually indicate decreased vulvar conformation or contamination of the culture instrument during the procedure.

Threlfall added that it is rare to see more than one infectious organism present on a culture. If multiple organisms are present in a culture, he recommends veterinarians re-culture to ensure accurate results are achieved before treating.

Endometrial Cytology--Endometrial cytology (a microscopic examination of uterine lining cell types) can provide rapid insight as to whether inflammation is present in the uterus, Threlfall said. "It does not replace endometrial biopsy and is not prognostic, but works excellently on the farm for additional information before breeding," he said. The presence of white blood cells in uterine cytology indicates there is a problem that needs further diagnostics to pinpoint.

Endometrial Biopsy--Threlfall described endometrial biopsy (evaluating a biopsy of the uterus lining) as a prognostic indicator and a diagnostic tool and said the procedure was best used in combination with uterine culture. He explained that biopsies are indicated in all breeding soundness exams, but especially important in cases of barren mares and mares with palpable abnormalities, pyometra (pus buildup in the uterus), or a history of early embryonic death. Based on biopsy, mares are graded on a four-category scoring system related to their probability of conceiving and maintaining a pregnancy to term: Grades I (70% or more of carrying a foal to term), IIa (50 to 70% of carrying a foal to term), and IIb (30 to 50% of carrying a foal to term). The category III has a less than 30% probability of carrying a foal to term. The categorization is based on inflammation and/or fibrosis (scarring). Inflammation is usually reversible with treatment, Threlfall said, while fibrosis has no treatment available.

Take-Home Message

Before breeding a mare, it's important to have a veterinarian perform a breeding soundness examination there is any indication of subfertility to ensure she's in optimal reproductive health. Breeding a mare with reproductive health issues could not only result in a sick or aborted foal, it could result in additional financial expenses for the owner and physical hardship for the mare.