Warning! This may be the longest blog post yet, so you may want to grab your beverage of choice and settle in before you start reading!

So this breeding season was a bust for your mare. You spent thousands of dollars, have no foal to look forward to next spring, and still don’t know why your mare isn’t pregnant.  Parts 1 & 2 of this blog covered factors related to management and to the stallion that may explain conception failure and now I’ll wrap up this series with a list of potential problems related to the mare herself.

I’m going to list potential problems by the area of the reproductive tract in which they occur, so we will move forward from the tail end of the mare towards the ovaries.  This is similar to the way I would examine any mare that came to me for an end-of-season breeding soundness exam (BSE). Basically, the BSE consists of these steps:

• history
• complete physical exam of reproductive tract
• laboratory samples
• ancillary diagnostics (doctor-speak for “tests I don’t usually do, but might be necessary in certain patients.)

The first step in figuring out what went wrong is taking a thorough breeding history. We’ve all read over and over how important it is to keep good records and it is especially crucial in evaluating a mare that has failed to conceive. If your mare has bred successfully before, look back at these records as well. You may notice that your mare seems to have problems becoming pregnant when she has a foal at her side, or that she seems to breed more easily later in the breeding season.  I could probably write 1500 words on history alone, but the main point is this: keep as detailed a history as possible and share this information with your vet! And have patience with us…we really do have reasons for asking all those questions!

When I’m performing a mare BSE, I actually start with the tail: is there any discharge present? Can I hear wind sucking as I lift the tail? Next, I examine the vulva: does the mare have poor vulvar conformation? Can I hear wind sucking if I pull the vulvar lips apart? If the mare has had a Caslick’s procedure (the surgery which closes the top portion of the vulva in order to protect the reproductive tract from fecal material) in place, is it long enough? Are there any small holes which may allow fecal material to contaminate the rest of the genital tract? Some mares may even additional vulvar reconstructive surgery when a standard Caslick’s procedure isn’t enough.

Moving forward (literally!) with the exam, I evaluate the vestibule and vagina, including the cervix. (**Note: no one should perform an invasive exam of the cervix without first confirming by palpation and ultrasound that the mare is not pregnant!) Potential problems to identify in this area of the reproductive tract include: urine pooling, fecal contamination from poor vulvar conformation or recto-vaginal fistulas, inflammation of the vagina &/or cervix, vaginal wall &/or cervical tears, and persistent hymen. Ask your veterinarian to perform both a speculum exam and a digital/manual exam to rule out these conditions.

The examination of the uterus is performed by transrectal palpation and ultrasound.  Here I’m looking for the presence of any type of uterine fluid, uterine cysts, edema, tone, myometrial “hernias” (localized atrophy of uterine muscle), and tumors or masses. Both the manual palpation AND ultrasound are necessary here-neither technique alone can tell you everything.

The next portion of the reproductive tract is the uterine tube or oviduct. (In humans, this is called the Fallopian tube, named after a famous human; in veterinary medicine, we use the more descriptive term of uterine tube!) This is the small, convoluted tube that connects the uterus to the ovary. It is a small body part with HUGE significance: this is where the sperm hang out while they wait for the egg cell to appear. Fertilization occurs here, and the fertilized egg actually remains here for 5-6 days before descending into the uterus. The uterine tubes/oviducts are very difficult to exam by palpation and ultrasound (I will come back to them when I get to the “ancillary diagnostics” section) but it is important to consider problems in this area as a potential cause for a mare’s failure to conceive. Uterine tubes can be blocked, atrophic (shrunken) or absent altogether in rare cases. Veterinarians used to believe that problems with the uterine tubes were extremely rare in the mare (as opposed to other animals like cows) but we are learning that these problems are more common and deserve investigation.

The ovaries mark the last point of the journey to thoroughly examine the mare’s reproductive tract. Like the uterus, they are examined by palpation and ultrasound.  I look for the presence of both ovaries (I know that sounds strange, but sometimes the previous owner will remove one ovary from a mare and forget to disclose that surgery to the current owner!) as well as normal size, shape, and texture. Using the ultrasound, I can identify follicles, corpora lutea, tumors, hematomas, etc. The actual egg cell, (oocyte, the female gamete) which is contained within the follicle, cannot be examined with palpation and ultrasound.  Unlike the male gamete (the sperm cell or spermatozoa) which can be easily collected and examined, the female gamete requires special aspiration techniques to harvest and examine.  It is quite rare to encounter true “menopause” in the mare (I have only seen two cases in 23 years) but this diagnosis  should be considered in mares that stop producing follicles altogether.

So far, I have taken a thorough history and performed a complete physical examination of the mare’s reproductive tract. Maybe the history and exam have pointed me towards a specific problem, but frequently I find nothing of great significance. Here’s when I get some help from the laboratory.  These are three standard diagnostic tests and what information they provide:

• Uterine culture- a swab of the endometrial surface (inside layer of uterus), aspiration of uterine fluid, or a low-volume lavage provide a sample that can be grown (cultured) to show if bacteria are present, what type of bacteria, and which antibiotics will be successful in treating an infection. It is VERY important to remember that the vast majority of mares with bacterial uterine infections show no outward symptoms; even if your mare doesn’t have discharge, she still may have an infection!! Ask your veterinarian to submit the sample to an experienced laboratory (and preferably one that specializes in veterinary diagnostics) and request an antibiotic susceptibility for any positive cultures. Finally, don’t forget to follow up antibiotic treatment with another culture to make certain that treatment was successful.
• Cytology- this is obtained in a similar manner as samples for a uterine culture, but instead of being cultured for the growth of bacteria, the sample is smeared on a slide, stained, and examined under the microscope to determine if inflammatory cells and/or bacteria are present. Cytology samples can also be taken with a special brush which helps to collect cells (similar to the Pap smear used in women.) This test can rapidly give us information about how inflamed the endometrium is and whether bacteria (or other microorganisms) are present. Cytology is NOT a replacement for uterine culture and biopsy, but can enable us to begin treatment while we are waiting for the other lab tests to be completed.
• Endometrial Biopsy- a small section of the endometrium that (almost miraculously!) can give abundant information about the rest of the uterus. Endometrial biopsy is probably the single most important tool in assessing a mare’s potential as a broodmare.  The biopsy sample is examined for three basic characteristics: inflammation, fibrosis (scar tissue) and problems with the endometrial glands. Samples are graded according to a system developed by Dr. Robert Kenney which correlates the biopsy category with the percentage chance of the mare conceiving AND carrying a foal to term. (We are breeding to produce live foals, not merely to produce pregnancies, right?) Category 1 mares are essentially normal and have an 80% or better chance of conceiving and carrying a foal to term; category 3 is the opposite end of the spectrum, with a less than 10% chance of conception and delivery of a live foal. Category 2 covers two subsections—ask your vet for all the details and whether this test is appropriate for your mare. Some of the changes that diagnosed with endometrial biopsy are treatable (for example, many inflammatory changes); some (fibrosis) are not.

This next section includes ancillary diagnostic tests that I consider to be “optional” in most mare BSEs.  I touched briefly on hysteroscopy which is the endoscopic exam of the uterus. This can diagnose some problems with the uterine tubes or oviducts, as well as provide a better view of unidentifiable objects seen on ultrasound such as lymphatic cysts and tumors. Laparoscopy (the use of an endoscope in the body cavities, but not in the uterus itself) may be necessary to further investigate problems with the uterine tubes, ovaries or uterus. Nutritional status can affect the reproductive system, so this may be an area to investigate with your veterinarian and nutritionist. (Please note that I used the word “nutritionist” not “owner of a feed store”! If you have concerns about your mare’s diet that your vet can’t answer, ask for a referral to an animal nutritionist.) Finally, there is the mysterious, ubiquitous “bloodwork” to discuss. If you have ever watched an episode of CSI, you know by now that there is no single blood test that will tell us precisely what we need to know to solve the case. The same is true in the mare BSE: there is no single blood test that will explain everything about why your mare isn’t pregnant. Based on your mare’s history and physical exam, your vet may want to investigate levels of specific hormones, indicators of metabolic disease, or trace minerals. Analysis of blood, serum, and plasma has a place in the mare BSE, but don’t expect these tests to give the entire picture!

To conclude our mare-focused discussion, I want to remind you that there are problems we can’t diagnose with any definitive test. Some examples that come to mind are mares that fail to conceive while nursing foals, mares that fail to conceive with certain stallions, and mares that have difficulty conceiving with frozen semen. Frustrating, yes; but often these problems can be ruled out over time by altering your breeding program. Remember the quote from Albert Einstein: “the definition of insanity is doing the same thing over and over and expecting a different result.” Maybe some of you have felt that the definition of insanity is breeding horses, but just like with childbirth, that newborn foal erases all thoughts of the difficult journey!

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