Find Reproductive Problems

Most of us associated with breeding mares and stallions can't wait for the season to end and don't want to think of barren mares and stallions until next year. However, the most opportune time to identify causes of infertility might be missed if you wait before performing a breeding soundness exam.

The most common mare reproductive problems are:

  • Mares that do not cycle properly or at all;
  • Mares that conceive and lose their pregnancies after 45 days; and
  • Mares that either don't conceive or lose their pregnancies before 40 days.

Different tests are conducted for each of the three problems.

If your mare isn't cycling properly, the hormonal signals from the brain are not getting to the ovaries, indicating that the mare has an endocrine problem. In addition to a rectal and ultrasonographic examination of the reproductive tract, blood needs to be drawn to measure hormones. If the cause of the endocrine problem is a tumor, it can be surgically removed. Most mares will cycle back within six to eight months. Other causes, such as Cushing's disease (hyperactivity of the adrenal cortex caused by a pituitary tumor that can't be removed), administration of anabolic steroids, stress due to pain (chronic laminitis) or performance anxiety, and "cystic follicles" due to old age are not as easy to correct. Mares with the latter problems need long-term management and frequent veterinary examinations.

Mares in categories two and three have normal endocrine function, but have defects in their reproductive tracts. Mares that conceive and abort after 45 days usually have degenerative fibrotic changes to the uterine glands. These changes interfere with the glands' ability to produce uterine milk, the secretions that nourish the embryo until the placenta attaches between 60 and 100 days. If the glands are not functioning properly, the embryo starves. This abnormality is identified by uterine biopsy, but there is no successful treatment. These mares usually make good embryo transfer candidates.

The most common mare fertility problem is uterine infection. Typically these mares have clean uterine cultures in the spring, then have bacteria isolated from their uteri after they have been bred three or four times. Two types of mares fall into this category--mares that have had three or four foals and cannot clear their uteri of the inflammatory by-products of breeding, and maiden mares with tight cervixes. The older mare accumulates fluid because her uterus is lower than her pelvis and the uterus cannot drain, and/or she has perineal defects resulting in self-contamination. Maiden mares become infected because the cervix does not open and drain properly after breeding. Mares in this category need a complete breeding soundness evaluation conducted when they are in heat, including rectal and ultrasonographic examination of the reproductive tract, vaginal examination, digital examination of the cervix, uterine culture, and cytology. Some of these mares might need reproductive surgery to correct perineal defects, urine pooling, or cervical lacerations. These mares should be re-cultured after treatment and a second cytology exam needs to be collected before they are given a clean bill of health.

Stallion Evaluation

For normal stallions, sperm numbers drop by 50-60% in the winter, and subfertile stallions may have an even greater decrease. This makes it difficult to properly identify what semen production might be next spring. For a new stallion entering stud service, it is important to conduct a breeding soundness examination before winter to determine the number of mares he can cover the following spring and to evaluate the longevity of his semen (if it is to be shipped).

Before stallions enter stud service, a breeding soundness examination should be performed. The exam can usually be performed in one day unless the horse has never mounted a mare. In this case, the horse can be taught to mount a phantom in a quiet environment so that he learns good breeding manners. If a horse has been used at stud, he should be rested sexually for a minimum of seven days before semen is collected. The breeding evaluation includes examination of the horse's libido, his breeding technique, and semen quality. The volume, concentration, motility, and morphology of the semen are determined. If semen is to be shipped, it is added to a number of extenders and the motility evaluated over 48-72 hours. Once the veterinarian has determined the best method to extend and process the semen, the farm manager or owner can be taught to correctly handle it. (A common cause of mare infertility is poor semen handling.)

About the Author

Michelle LeBlanc, DVM, Dipl. ACT

Michelle LeBlanc, DVM, Dipl. ACT, is a theriogenologist (reproduction specialist) for Rood and Riddle Equine Hospital in Lexington, Ky. She was previously a professor in equine reproduction at the University of Florida. Her interests deal with mare infertility, embryo transfer, placental infections in mares, and acupuncture in infertile mares. She owns Thoroughbred/warmblood crosses and she competes in dressage.

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