Mare Breeding Soundness Exams

Getting to the root of a problem mare’s breeding challenges takes some investigating. 

By Megan Arszman; Photos by Kaycie Timm

Buckskin broodmare by pond
Is your mare ready to be bred? A breeding soundness exam can identify potential problems, saving you time and money in your effort to have a foal on the ground next year.

Breeding a mare, whether she’s a maiden or veteran broodmare, is one of the biggest gambles a horse owner may ever take. It can be time-consuming and expensive. If a mare has issues conceiving or carrying a foal to term, having a breeding soundness examination (BSE) performed on the mare by a veterinary reproductive specialist is a worthwhile investment. 

What’s a BSE?

A BSE looks at the broodmare’s reproductive and physical factors, including her weight, conformation, overall health, and reproductive organs. The exam’s scope can vary depending on the mare’s history, the owner’s needs, and the vet’s assessment. 

Who Needs a BSE?

Having a BSE performed on a broodmare annually isn’t always necessary, says Margo Macpherson, DVM, MS, Dipl. ACT, and a professor at the University of Florida’s College of Veterinary Medicine. However, a mare with a history of reproductive problems will likely need a BSE. 

“My rule of thumb is if there has been a problem in the past, I’ll want to evaluate the mare,” Macpherson says. “Often, that means a mare has been unsuccessfully bred two or three cycles with semen from a fertile stallion and with good breeding management. It’s less common to evaluate a maiden mare, especially if she’s young. In that case, I’m inclined to try breeding the mare rather than performing a BSE.” 

An exception to this scenario is the evaluation of a mare to serve as a recipient for an embryo. The donor mare may or may not benefit from a full BSE. The recipient mare, however, should be evaluated for her ability to carry an embryo to term and care for the foal. 

“There have been studies on the effect the recipient mare’s reproductive soundness has on the success rate of an embryo transfer,” Macpherson says. “Some important things are the mare’s age, reproductive status, and health, which is why I’d absolutely insist on a BSE for recipient mares.”

But Macpherson cautions that there’s no set rule concerning which mares should have BSEs and which mares won’t need one. 

“None of this is recipe-driven,” she says. “Every mare is an individual, and every owner is an individual. So, the best place to start is understanding the owner’s endpoint and having as much information as possible about the mare’s past and present to assist in that pursuit.”

Breeding History 101

The first, and perhaps most important, part of a BSE is understanding the history of the broodmare’s reproductive career, Macpherson says.  

“I want to know about the history because, to me, one of the biggest reasons why a mare isn’t getting pregnant is missed information in breeding management,” she says. “Breeding management is a big component of the pregnancy’s success, so it’s important to know the steps taken to achieve that goal.”

Basic records for your broodmare can consist of her age, performance record, vaccination history, and nutrition.

The most important records to keep for a broodmare are her reproductive history, including cycles (dates, length of heat, etc.), breeding dates, type of semen used (fresh, cooled, frozen), reproductive success of the stallion (first cycle and seasonal pregnancy rates), pregnancies carried to term or embryo recovery rates, abnormal pregnancies, dystocia/assisted foalings, and post-foaling problems (retained placenta, metritis, trauma, bleeding, etc.). Having this information is not only helpful to the breeding farm, but also to the veterinarian. 

“I do a lot of consults over the phone, so having proficient records goes a long way,” Macpherson says. 

mare and foal in pasture
A breeding soundness exam not only covers all of your mare’s reproductive organs, but also her ability to feed and raise a foal after delivery.

Overall Physical Examination

A veterinarian will first look at the overall physical condition of the broodmare in question. A healthy broodmare should be around a five or six on the Henneke Body Conditioning Score, meaning individual ribs can be felt (but not seen); her rump and tailhead are cushioned; and there are some slight fat deposits along the withers, behind the shoulders, and along the neck.  

One of the easiest factors to address in breeding soundness is optimal weight/conditioning. Mares that are significantly underweight have poor pregnancy rates, often as a result of compromised reproductive conformation, which leads to infection and contamination of the internal reproductive tract. Obese mares also have poor pregnancy rates, and Macpherson says mares with equine metabolic syndrome are a good example of obesity and poor fertility. 

Evaluating the perineal area is an important part of the initial physical examination. Ideally, the mare’s vulva will have good apposition to the lips; there won’t be a significant tilt to her perineal area; and the anus won’t be sunken. If the mare has previously carried foals, any damage to the vulva/perineal area should be noted and, if needed, addressed with a Caslick’s suture. Macpherson also looks at the mare’s mammary glands, which is sometimes an overlooked area. 

“We’re not just worried about getting the mare pregnant, but also how she carries the pregnancy to term, delivers the foal, and cares for that foal in the end,” she says. 

Investigating Further

Next, the veterinarian will perform a transrectal palpation and ultrasound. The palpation allows her to evaluate the reproductive structures and texture. Transrectal ultrasound examination of the reproductive tract can reveal normal findings such as follicular size and uterine edema, as well as issues such as uterine fluid, cysts, and/or ovarian/follicular abnormalities. 

To perform a complete BSE, Macpherson stresses the importance of investigative options such as uterine culture, cytology, and/or uterine biopsy. 

“A uterine culture and cytology will show us if the mare has infection or inflammation present in her uterus, which would reduce her chances of becoming pregnant,” Macpherson states. “An endometrial biopsy is a tool that allows us to look more closely at the uterus using a microscope, rather than just using an ultrasound at the farm.”

A uterine biopsy can reveal changes like scar tissue, also called fibrosis, which can impair the uterus’s ability to stretch and contract. If fibrosis is prevalent, it often causes a permanent issue that can affect the mare’s fertility with little to no prescription to assist with the problem. 

A Reproductive Insurance Policy

Breeding horses isn’t a cheap hobby. Having a BSE performed on your broodmare, whether she’s a new purchase or a veteran, is like an insurance policy for your investment. 

“I think education and information are important when making breeding decisions, particularly in aged or subfertile mares,” Macpherson stresses. “If you go into breeding season knowing that your 18-year-old broodmare has reproductive conditions that will make it challenging for her to get pregnant, she can be managed differently and there will be fewer surprises. As veterinarians, it’s good to be prepared to do our best to get the mare pregnant while also having realistic expectations, for both ourselves and the owner, about a mare’s chances for success. 


Margo Macpherson , DVM, Dipl. ACT, is a professor at the University of Florida’s College of Veterinary Medicine. A former president of the American College of Theriogenologists, Macpherson is primarily interested in conditions that affect pregnancy in horses, including twin pregnancies and placentitis.