Managing Barren Mares

Not every mare that is mated during a breeding season becomes pregnant, nor does every mare that conceives carry a foal to term. Failure of conception, early embryonic losses, and abortions are a fact of life in equine reproduction, and problem mares must be managed properly for the following breeding season.

In 2001, Kentucky and several other areas had an added problem with mare reproductive loss syndrome (MRLS), in which many early- and late-term pregnancies (stillborn and weak foals) were lost. The theories abound as to the cause of this syndrome, but to date the cause remains unknown.

Management of barren mares, whatever the cause, should be addressed well before the subsequent breeding season. A standard breeding soundness examination should be conducted on these mares. This includes a complete assessment of the mare's health and reproductive history, a general physical examination to identify any underlying or overt physical problems, examination of the mare's perineal conformation, rectal palpation, ultrasound, speculum and manual examination of the vagina and cervix, uterine culture and cytology, and endometrial biopsy. These areas should be addressed in every barren mare. If additional information is still required, ancillary procedures such as uterine endoscopy, hormonal profiles, and karyotyping (chromosome analysis) can be done.

No matter what problems your mare has, a complete and thorough reproductive history is important in planning a subsequent course of action. Examining teasing charts from the previous year or two is extremely helpful. Equally important is information on the fertility of the stallion or stallions to which the mare was mated and whether the mare was bred with natural service or artificially inseminated with fresh, cooled, or frozen semen.

A mare should not be too thin or be overweight. The perineal region should be examined, and if the conformation warrants, a Caslick's procedure (to partially close the vulva, keeping external contaminants out) performed.

Rectal examination of the mare's reproductive tract and an ultrasound examination of the uterus and ovaries should be performed. Just palpating the reproductive tract might not pick up uterine fluid or detect ovarian or other abnormalities. In addition, this examination will verify the pregnancy status of the mare. Speculum examination of the vagina and cervix along with a digital examination is necessary to detect abnormalities such as cervical tears and failure of the cervix to dilate or close properly (depending on the stage of the estrous cycle). In addition, urine pooling can be detected with this method.

Assessment of endometritis (uterine infection) can be made by uterine culture in conjunction with uterine (endometrial) cytology. The cytology will detect inflammation in the uterus, and culture will detect the type of bacteria, yeast, or fungus that is causing the inflammation. If a culture alone is performed, a small growth of an organism will not tell us much without the cytological results.

An endometrial biopsy can give more details on the lining of the uterus. The health of the uterus can be graded to give a prognosis for carrying a foal to term under proper management.

These examinations should be undertaken long before the breeding season. In this way, any correctable conditions can be addressed so that the mare will be presented in the best possible condition at the beginning of the next breeding season.

Mares that were "victims" of MRLS should be evaluated the same way. However, in my opinion, it does not appear that these mares suffered any long-lasting damage to the reproductive tract. It is highly unlikely that the same conditions that played a role in this syndrome will repeat themselves in the near future.

Even after all of the examinations, treatment, and management adjustments, some mares will not conceive or carry a foal to term. We must remember that from the mare's side, the ovaries and uterus are not the only players in this game. At birth, a female foal is born with all of the eggs she will have for her lifetime. So, an 18-year-old mare has 18-year-old eggs! With aging, changes can take place in those eggs that result in early embryonic death or no conception. In addition, there are numerous biochemical and genetic "controllers" of pregnancy that must turn on and off in specific sequences to facilitate conception, development, and subsequent birth of a foal.

Also, we should not forget the stallion's role. The use of a stallion that is highly fertile will increase the chances of pregnancy. Timing of mating and method of breeding might play a role in whether a mare becomes pregnant. With natural service, getting to very busy stallions at the correct time can be difficult. The use of frozen semen, however, has generally resulted in lower conception rates per cycle than the use of fresh or slow-cooled semen.

About the Author

John Steiner, DVM

John Steiner, DVM, is associated with the Hagyard-Davidson-McGee veterinary firm near Lexington, Ky., and specializes in reproductive problems.

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