Reproductive Challenges: Barren Mares

The anticipation and jubilation surrounding the arrival of the first foals of the new year have come for many of us. It is interesting how transient that celebration is. In fact, we are applauding Mother Nature and the victories of last year's early breeding endeavors and realize the next contest is about to begin anew and in earnest. We have a fresh set of mares which for one reason or another have become the reproductive challenges of this season, and preparation for the game is immensely important. It requires a well-orchestrated team effort among the mare owner-manager, breeding sheds, and veterinarians. The opposition is as diverse as it is formidable. Some mares will conceive with one cover and foal next January. There are others in the group which should not even be bred. Now is the time to sort out the opportunities.

As with most contests, there are obstacles. The first obstacle is that these challenging mares must conceive in the depths of winter. This encumbrance has necessitated the use of artificial lighting to shorten the mares' transitional period. I mention this only briefly because lights (16 hours/day) alone do not a cycling mare make. Day length (photoperiod actually), temperature, and nutrition will contribute to shortening the transitional period. Day length (light) and nutrition we can manage. Temperature, in most cases, we cannot. It is extremely important that the nutritional state of the barren mare be closely and individually monitored, especially in extremes of temperature. The caloric requirement of a barren mare at 45 degrees is significantly different than at 15 degrees, no matter how "illuminated" she may be!

Mares which are stressed--nutritionally or otherwise--do not cycle well. Ideal weight is an individual phenomenon that is not seasonal. To starve a mare in the winter so she will be in foal early has never made a lot of sense. Mares appreciate consistency, and the nutritional plane on which they exist is the basis for all other management practices. Proper foot care, dental care, deworming, and vaccinations all reduce stress and improve a mare's chances for conceiving early and uneventfully.

The next arena to be entered is the physical status of the reproductive tract, both external and internal. Caslick's procedures are always mentioned because the vulvar barrier is the single most important defense system we can surgically buttress for the challenging mare. Careful assessment of this critical seal can improve her chances immensely. Cervical injuries or anomalies which are amenable to surgical intervention often come to light at this time and should be addressed, as should the chronic urine pooling mare. Acupuncture is providing some interesting and successful alternatives to treating urine pooling and should not be overlooked.

It is often the endometrial status that has earned these mares membership in the "elite" group. Culture, cytology, biopsy, ultrasound, and hysteroscopy all provide information about the preeminent lining of the uterus. The more information we can glean prior to breeding, the better. It is often more of a mistake to overmanage than undermanage the endometrial surface, and knowing what you're up against is the best defense.

Hysteroscopic examination often reveals abnormalities that cannot be determined with other modalities and is quite easily performed. Mares with a three-year barren history, with irreducible uterine adhesions, and a grade III biopsy may be best left to eat grass with their pasturemates. Hysteroscopy also provides a three-dimensional look at endometrial cysts which, depending on size, number, and location, may warrant removal with laser surgery or alternative methods.

The next anatomical opportunity arises at the oviducts, the vital link between the ovaries and the uterus. A mare with occluded oviducts will not conceive, end of story. However, surgical intervention can re-establish tubal patency and allow a mare with a dismal produce record to get back into the foaling mare band. On the other hand, if both oviducts are irreparably occluded, there is no reason to expend a great deal of mental energy (and money) on a no-win contest. Surgery does provide a viable alternative and can be extremely rewarding in the appropriate cases.

Ovarian status coupled with endocrine assessment covers the final page of the scouting report. Manual and ultrasound examination of suspect ovaries may reveal abnormalities that have contributed to subfertility in the past. Endocrine imbalances, specifically thyroid hormone, can be inexpensively resolved and appear to have significant reproductive implications. Testosterone, FSH, LH, estrogen, and progesterone levels all can provide information that makes the job easier.

Having best prepared the mares for breeding, the most critical management area for the reproductive challenge is post-breeding intervention. A large volume of recent research in equine reproduction has focused on subfertility and reduced uterine clearance (RUC). In a nutshell, all mares develop inflammation in the uterus post-breeding, whether it be natural service or AI. This is normal and necessary. The problem arises with certain mares which are unable to limit and clear this inflammatory environment from the uterus prior to the arrival of the embryo. There are actually three mechanisms by which normal mares clean inflammatory debris and fluid from the uterus. What appears to be the most compromised in subfertile mares is actually myometrial (uterine muscle) activity. The use of oxytocin and/or prostaglandin coupled with uterine lavage and antibiotics can augment the myometrial clearance of retained fluid. Timing of post-breeding intervention and actual procedures vary with individual mares and should be a pre-established part of the game plan.

What is often seen with ultrasound in very difficult mares which haven't been in foal in years is at 14-16 days post-ovulation, there are two mirror-image embryos apparently glued together and surrounded by some very attractive, symmetrical endometrial cysts. This issue, along with maintaining the pregnancy until term, is great material for owner-manager and veterinarian dialogues throughout the rest of the season.

Let the games begin!

About the Author

Chet Blackey, DVM

Chet Blackey, DVM, is a private equine practitioner based in Versailles, Ky., and a member of the AAEP Reproduction Committee

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