If a mare isn’t getting pregnant after multiple breeding attempts to a stallion with good fertility, it is important to determine why. Reasons could be many, and veterinarians commonly use diagnostic techniques such as endometrial culture, cytology, and biopsy to pinpoint the cause. Karen Wolfsdorf, DVM, Dipl. ACT, of Hagyard Equine Medical Institute, in Lexington, Kentucky, described how at the 2016 American Association of Equine Practitioners Convention, held December 3-7 in Orlando, Florida.

Investigative Tools

Wolfsdorf said culture involves determining if bacteria are present within the uterus, and if so, what kind and to what antibiotics they are sensitive. Cytology involves using a microscope to look at the individual cell types and substances the endometrium produces, and biopsy is the examination of the endometrial tissue as a whole.

Low-volume lavage is a useful way to get the most representative sample of what’s in the uterus, including cells, bacteria, mucus, and debris. During this process, the veterinarian flushes one liter of sterile solution into the uterus and then collects the fluid in a sterile container. After spinning the fluid in a centrifuge, he or she swabs cells from the remaining sediments that have sunk to the bottom, putting them on culture medium to grow bacteria and on slides for cytologic microscopic examination.

A biopsy of the endometrium is particularly important for predicting a mare’s likelihood of carrying a foal to term, and it helps the veterinarian identify underlying abnormalities not seen on culture, cytology, or ultrasound examination, said Wolfsdorf. The practitioner can take single or multiple samples from questionable areas and evaluate those details. He or she can examine endometrial tissue for inflammation, density and nesting of endometrial glands (when secretions get trapped in the base of the glands), fibrosis (scarring), and lymphatic and vascular (blood vessel) changes. By identifying these changes, the vet can begin appropriate management and treatment.

Uterine Conformation

Uterine placement within the abdomen and perineal conformation affect fertility. Wolfsdorf pointed out that many subfertile mares have a uterus that hangs loosely and sits toward the mare’s head (cranially) and bottom (ventrally) due to stretching of the broad ligament that supports the organ. Stretching occurs with age and multiple pregnancies, decreased uterine contractility, and poor perineal structure. These physical alterations leave the mare’s uterus susceptible to bacterial invasion and decreased uterine clearance—the natural expulsion of foreign material after breeding—causing fluid, mucus, and other debris to accumulate. Any of these factors could negatively impact a mare’s ability to become pregnant, said Wolfsdorf.

Take-Home Message

A thorough examination of a subfertile mare is important to assess her reproductive health. Don’t forget to consider stallion fertility, as well, before placing all the blame on the mare! Understanding the underlying changes causing a mare’s reproductive issue is essential for formulating a proper course of treatment and management.