With breeding season just around the corner, it's time to start planning your management of open mares. Nothing drains your enthusiasm and your bank account more than mares who don't produce foals. Open mares who are "problems" are those whose fertility has been declining over time due to irregular cycles, failure to ovulate, recurrent uterine infection, or repeated pregnancy loss.

Regardless of the cause, basic management is critical in handling these mares. You must be able to determine when the mare is receptive to a stallion and you must be able to document ovulation. The first requirement is best accomplished by teasing on a regular schedule, and the second by having your veterinarian examine the mare. Then you must keep accurate records.

If you haven't used lighting systems to advance the season, don't get impatient and breed the mare before she has established a good cycle with short heat periods and predictable ovulation. Much damage is done by breeding mares too often during a given estrus. In temperate zones, the average first ovulation of the season is in April!

Prior to breeding the mare, she should be examined, during estrus, to determine the following: presence of a pre-ovulatory follicle, lack of fluid in the uterus, no evidence or signs of uterine inflammation (redness of the cervix or vagina, discharge from the cervix or vagina, positive uterine cytology). These determinations require rectal palpation of the reproductive tract, visual vaginal examination, a swab to collect a cytology specimen, and ideally, ultrasound evaluation of the uterus. If there are signs of inflammation, a culture is indicated to identify the cause. (Some farms require a negative culture before they will breed your mare, but negative cytology is more reliable as an indicator of uterine health.)

Mares that have positive signs of inflammation may require treatment before they are bred. The decision to treat, and with what, must be based on history, the cause of the inflammation, and the overall assessment of its significance. You and your veterinarian need to discuss the situation and agree on a course of action. There is a growing tendency by some practitioners to avoid infusion of antibiotics in favor of uterine lavage or other alternative therapy. This is based on experiences with resistant bacteria or yeast infections after prolonged antibiotic use.

It is important to understand the concept of uterine resistance when managing a mare with a history of recurrent infection. All mares develop an inflammation after breeding. If that process is resolved quickly, pregnancy is possible. If the inflammation drags on for days, the embryo will not survive. Thus, mares resistant to infection are those with effective defense mechanisms.

A key factor in uterine resistance is the ability of the uterus to empty itself after inflammation begins. Dr. Michelle LeBlanc, at the University of Florida, has demonstrated this very clearly (MHB, January 1995, pages 16-17). She has shown that treatment to enhance uterine clearance after breeding is indicated in more than 60% of mares with recurrent endometritis. Treatment administered 8-12 hours after breeding with oxytocin or oxytocin plus uterine lavage resulted in significant improvement in conception.

Mares that may benefit from this treatment are those that remain actively inflamed several days after breeding. This can be confirmed by finding fluid in the uterus (using ultrasound) seven days following breeding. Another highly suggestive sign is a positive cytologic exam when the mare returns to heat.

While recurrent infection is a major source of reduced fertility in mares, there are several other common problems with which to contend. Most can be resolved by good husbandry and management practices used in conjunction with veterinary expertise and advice. When good managers team up with veterinarians, positive results are most likely to follow.

A. C. Asbury, DVM, is the chairman of the Department of Large Animal Clinical Sciences at the University of Florida College of Veterinary Medicine.

Reprinted from The Horse: Your Guide to Equine Health Care

Permission has been granted by AAEP for this one-time reprint.