Thinking About Breeding Your Mare? Understand Breeding Soundness Exams for Your Mare

 Foal peeking head around mare.

Are you thinking of breeding your mare? If so, it is recommended that your mare receives a breeding soundness exam.

A breeding soundness exam involves a complete evaluation of the reproductive potential of your mare, using history, a full physical exam, and multiple diagnostic procedures. This allows your veterinarian to determine if your mare is physically able to get pregnant and support a foal to term, if she would be better used as an embryo transfer donor, or if more advanced reproductive technologies would be needed to produce a foal.

Breeding soundness exams can be performed prior to breeding, as a part of a pre-purchase examination, or if a mare is having trouble getting into foal. Performing a breeding soundness exam approximately 60 days before a planned breeding can alert you to potential problems that can be treated before breeding even begins, saving you a lot of time, money, and frustration.

Complete Health History

I begin by getting a complete history on your mare. Here are some of the questions I ask:

  • What is your mare’s age?
  • What is her health management program (e.i., vaccinations, dental care, farrier care)?
  • Has she had any previous breedings/pregnancies, and what breeding method was used?
  • How many previous foalings has she had and when?
  • Has she had any history of foaling problems?
  • Does she have a history of stillbirths/abortions, and what was the fetus’ gestational age at loss?
  • What were the results of prior fertility exams/ultrasound examinations?
  • Have there been previous reproductive tract infections and treatments?
  • How is this mare’s mothering ability?

If you have previous breeding records, these are great to bring to the exam so they can be analyzed for any patterns of concern.

Physical Exam

Next, I perform a complete physical exam on your mare. Proper identification using registered name and number if applicable, color, markings, brands, tattoos, etc. is extremely important. The physical exam is extensive, starting from the front end of the horse and ending at the back, looking at her eyes, teeth, weight and body condition score, gait soundness, fecal analysis, and other diagnostics.

The mare’s mammae, or udder, is examined to see if both sides are symmetrical, if they look as if a mare has nursed before, if there are anatomical issues that may not allow a foal to nurse normally, and even if she'll let me touch them without much trouble.

The final portion of the external physical exam is visual examination of the external genitalia. When observing the perineal area, I look for old scars from possible tearing, lacerations, and tumors.

 Good and poor vulval conformation of the mare

I assess the conformation or straightness of the vulva to determine if the mare is more prone to fecal contamination of the vagina and vestibule, or if she has the tendency to be a "windsucker." These mares have poor closure of the vulvar lips which allows air to enter the vestibule and vagina, causing mechanical irritation to the cervix and resulting in poor fertility or embryonic viability. Mares with poor vulvar conformation are candidates for a Caslick’s procedure, which surgically closes up the top portion of the vulva to prevent any contamination of the reproductive tract. After successful breeding, the Caslick is opened approximately 4 weeks prior to foaling.


The next step in the breeding soundness exam is palpation of the uterus per rectum. I do this first without the ultrasound in order to feel for anything abnormal, get a good feeling of the tone of the uterus, and to make sure I can feel all the normal parts of the reproductive tract – as well as anything abnormal, such as a hematoma in the broad ligament (indicates a serious bleed at the last foaling – this will be a high-risk pregnancy!).

I feel the ovaries and make sure they are of normal size and that palpable ovulation fossa is evident. A classic symptom of granulosa cell tumor is ablation of the ovulation fossa, even if the ovary isn't overly enlarged just yet. I also make sure there isn't anything abnormal about the shape of the uterus or the cervix.

 Dr. Allison Kiser performs ultrasound on mare during breeding soundness exam

Then I do the ultrasonographic exam to visualize the uterus, determine edema (which correlates to what stage of the estrous cycle the mare is in), check any fluid content within the uterus itself, identify follicle size on the ovaries, find and document any uterine cysts, and look for any other abnormalities.

Next, a culture and cytology of the uterus is performed. Even though we routinely do a swab culture, the new and more accurate collection method is by low-volume lavage. This entails infusing about 100 ml of sterile fluid into the uterus, milking it throughout the body and horns of the uterus by trans-rectal manipulation, then collecting the fluid. The fluid is spun down and the pellet swabbed for culture. This gives a more uniform representative sample from the entire uterus, since a swab only cultures one area. This is especially important as we note increased issues with biofilm plaques causing mare sub-fertility and infertility, as a plaque can be located anywhere in the uterus and may not be reached by the swab.

If an organism is found, its sensitivity to antibiotics or antifungals is obtained in order to determine the best course of action. The cytology is collected with a double guarded swab or brush and stained to look for normal endometrial cells and any inflammatory cells, bacteria, or fungal hyphae. While I have a hand in these mares to collect these samples, I also do a digital exam of the cervix to feel for any tears, fibrosis, or other abnormalities.

Next, I perform the vaginal speculum exam, which allows for visualization of the vestibule, vaginal vault, and cervix. I can tell if the vestibulovaginal seal is intact by the way the speculum passes through into vagina (it will suck the plastic wrapper in, which i keep over the end of the speculum until I'm ready to look in, for that purpose, and because the mare will get uncomfortable when air is rushes into the vagina).

I look at the color and shape of the cervix: is it pale and tight and lifted off the vaginal floor? Or is it pink and flaccid? Does that correlate with what I saw on the ovaries? I look for any blood, pus, or urine on the vaginal floor. I look for signs of irritation, lacerations, scarring/fibrosis, and varicose veins in the vagina and vestibule. Finally, I watch the whole way as I pull the speculum out slowly to make sure the vestibulovaginal fold closes behind me. The vestibulovaginal fold acts as a physical barrier to infection and if it does not seal properly, a Caslicks may be necessary.

Finally, I perform one of the most important diagnostics of the breeding soundness exam: the endometrial biopsy. In order to perform a biopsy, a long, specialized biopsy instrument is inserted through the cervix, then guided transrectally to the base of one of the uterine horns. The biopsied tissue is looked at on the cellular level for epithelium size/shape, glandular fibrosis, lymphatic lacunae, inflammatory cells, and any other abnormalities.

The sample is graded using the Kenney-Doig classification scale of uterine biopsies, which correlates with a percentage of prognosis for supporting a foal to term. Based on what is found on the biopsy, we can determine if these are permanent changes or not, if the mare can be treated and how she should be treated, and/or if she would be better used as a embryo donor candidate.

 Kenney-Doig Grade Scale of Uterine Biopsies

Ancillary Procedures

Other ancillary procedures can be used during breeding soundness exam if deemed necessary. One procedure that is gaining more popularity is hysteroscopy, or inserting an endoscopy camera into the reproductive tract to allow visualization of the entire uterus. We can definitively diagnose bacterial biofilm plaques, cysts, and/or other space-occupying lesions like transluminal adhesions and see if are blocking access to the uterine horns or oviductal papillae.

Genetic testing can also be performed on your mare to determine if she is a carrier of certain genetic diseases (HERDA, HYPP, GBED, PSSM, OLWS, etc.) and to be aware of before choosing a stallion that may also be a carrier.

Breeding season is right around the corner! Schedule your mare's breeding soundness exam with Dr. Allison Kiser of Badger Equine Veterinary Services today!