Older Mares: She Ain't What She Used to Be
The aging process takes its toll in many ways on horses and humans. When women reach a certain age, for example, they experience menopause, a transitional period when Nature serves notice that they no longer can bear children. With horses, that stage of life is less pronounced, with some mares capable of bearing foals almost up to the time of death. Producing a foal year in and year out takes its toll on the overall health of a mare, and the wear and tear on the reproductive system often makes it more and more difficult for her to conceive and carry a foal to term. The advances of science have given the breeder more tools with which to combat the aging process, but eventually time will win out and the mare will become barren. Until that time arrives, however, many breeders will continue to strive for "just one more foal."
Getting the older mare in foal requires time, diligence, investment, and expertise. It also requires special attention to such details as nutrition and overall good health.
Whatever the reason, or reasons, for breeding an older mare, the owner should begin with knowledge about the aging mare's reproductive tract, her nutrient needs, and the special care--and its cost--that she might require. The cost can be significant, depending on what the mare requires in the realm of medical help.
Just maintaining a horse is not cheap. In places like Kentucky, with its major Thoroughbred and Saddlebred farms, estimated costs are between $4,000 and $5,000 per year just to maintain a horse. The same wouldn't be true on a Wyoming ranch, but grass is precious on dry rangeland and maintaining an aged mare which doesn't produce a foal in that locale is considered an unneeded expense.
When breeding the older mare, the most important thing for the horse owner is to form an alliance with a trusted veterinarian experienced in equine reproduction. The decision of whether to even attempt breeding the aged mare should begin with the veterinarian performing a thorough reproductive examination.
Only if the veterinarian gives the mare a clean bill of health should the owner consider investing in a stud fee. However, it also should be noted that a number of problems can be beyond the scrutiny of even the most talented veterinarian.
For example, a study at the University of Wisconsin (UW), reported by Elaine Carnevale, DVM, PhD, now at Colorado State University (CSU), demonstrates that problems in the reproductive process can exist in the ovaries. The study indicated that ovarian failure was associated with advanced age--mares 20 years of age and older. This would not be evident during a breeding soundness examination.
The researchers found that older mares, compared to younger mares in the study, often had later emergence of the ovulatory wave of follicles, slower growth of the ovulatory follicle, a longer interval between ovulations, a longer follicular phase, and less of a luteinizing hormone surge.
Another UW study found that mares at least 15 years old had significantly more inflammatory and degenerative changes in the uterus and less uterine contractile activity than young mares. These changes can also be found in the oviduct, but they are not usually found unless a necropsy is done.
If degenerative changes in the uterus are so significant that the mare is unable to carry a foal to term, the reproductive answer might involve embryo transfer. In this procedure, the older mare is bred and becomes pregnant. However, rather than allow her to attempt to carry the foal to term, the embryo is removed and transferred to the uterus of a younger, healthier mare.
This procedure is becoming more successful with research and increased expertise of individuals involved in the equine reproductive process. However, it is not a panacea. There are drawbacks--one is cost.
Michelle LeBlanc, DVM, Dipl. ACT, of Rood and Riddle Equine Hospital in Lexington, Ky., outlined the procedure for a large crowd at Horseman's Day during the American Association of Equine Practitioners (AAEP) convention in late 2002. She told the group that embryo transfer has become a relatively commonplace procedure in the equine industry, especially with the establishment of larger recipient herds throughout the country.
Mean pregnancy rates per cycle--if both the mare and stallion are fertile--are about 50-60%, she said. Rates drop precipitously if horse is sub-fertile or if the recipient quality is poor. Keep in mind that pregnancy rates are the end result of a successful embryo flush procedure from the donor in conjuction with a successful transfer procedure into the recipient, and only if both mares are highly fertile can you expect to achieve optimum results.
Then LeBlanc addressed the matter of cost. The average cost of a successful embryo transfer, she told the group, ranges from $5,500 to $7,500. "Therefore," she said, "if a mare owner is to break even, the foal needs to be worth a minimum of $10,000-$12,000 at weaning."
Cost might not be an insurmountable obstacle for a major breeder who is producing foals which will sell for that kind of money at weaning time, but it might be the proverbial straw that breaks the camel's back for the backyard breeder.
In some cases, the problem within the uterus can be treated and the older mare becomes able to carry the foal to term.
At the AAEP convention, Scott Bennett, DVM, owner of Equine Surgical Services Hospital in Simpsonville, Ky., and an associate, Richard Griffin, DVM, MS, reported on a procedure they have used with great success to remove endometrial cysts that have been implicated in infertility of the older mare. The cysts within the uterus were of varying sizes and locations.
Involved in the study were 52 mares (three mares were evaluated twice) aged 13-24 years which had been barren for at least one season. Twenty-nine of the mares were treated at the Simpsonville hospital in the year 2000, and 23 were treated in 2001. The cysts were destroyed via laser treatment.
Of the 29 mares treated in 2000, 25 were located for further information. Of the 25 that were located, 18 had conceived in either 2000 or 2001. These mares, Bennett and Griffin reported, were bred an average of 2.3 cycles per conception after the procedure. Mares which conceived had been afflicted with an average of six cysts per mare.
Follow-up data was obtained on 14 of the mares bred in 2001. Of this group, eight conceived and six did not. The mares which conceived were bred an average of 1.4 cycles per conception and had an average of seven cysts before treatment.
As mentioned earlier, the older mare's reproductive problems sometimes occur before the egg reaches the point where it can be fertilized. Again, science has stepped in and made significant contributions. One of the procedures to overcome this problem is oocyte transfer. The procedure was developed in 1999 at CSU, and research has continued there and at other research institutions around the country.
The procedure involves transvaginal, ultrasound guided aspirations. In this procedure, the egg is removed from the follicle. Then the mature egg is transferred to the oviduct of a recipient mare. (The recipient mare's own follicles might have been removed, or she might have had her ovaries removed before the oocyte transfer, or she might be a non-cycling mare that was hormonally treated.) The recipient mare is then bred. If the oocyte is immature when collected, it is allowed to mature in the laboratory, then is transferred to the recipient.
An offshoot procedure that has been especially challenging involves attempting to inseminate the oocyte prior to transfer with a single sperm (called intracytoplasmic sperm injection, ICSI, in human medicine). Researchers at CSU have succeeded in accomplishing this, but to this point haven't been successful on a large scale.
Still another procedure is known as GIFT--gamete intrafallopian tube transfer. This technique involves harvesting an egg from a donor mare and depositing it and sperm from a stallion into the oviduct of a recipient. This process helps sub-fertile stallions as well as sub-fertile mares, because fewer sperm are used than in a normal artificial insemination procedure.
All of the above approaches have been successful in assisting reproduction in older mares, but it should again be noted that specialists are often required, and that it can become an expensive proposition.
One area in which an older mare can be helped without veterinarians involves nutrition. P.G. Gibbs, PhD, Dipl. ACAN, of Texas A&M University, addressed this at the first Horseman's Day held in San Antonio, Texas, at the 2000 AAEP convention.
Body condition, he said, might be the single largest factor affecting mare reproductive performance. Those maintained in moderate condition cycle earlier in the year, require fewer cycles per conception, have a higher pregnancy rate, and are more likely to maintain pregnancies than thin mares.
He explained a body scoring system that usually ranges from 1 to 9. A mare at the bottom of the range is emaciated and a mare at the top of the range is obese.
"Using this system," he said, "research has determined that a mare in a condition score of less than 5 may not have enough stored body fat to support efficient reproductive performance. Those mares are more likely to skip a breeding season than are mares with a condition score of 5 or more. This is especially prevalent in mares that are 15 years of age or greater."
Exactly what nutrients are required in what quantities can vary, but it's important to make sure the mare eats enough digestible energy. In some cases, it might involve a specially formulated or pelleted feed.
Several hormone treatments can assist in timed ovulation and in maintaining a pregnancy. Two of the best known are Regu-Mate, a synthetic progestogen that can be used to help a mare maintain pregnancy, and Ovuplant, a gonadotropin-releasing hormone that results in a consistent ovulation time once a mature follicle is present. However, owners should understand that many scientists believe that the use of synthetic progestogens to support advanced pregnancies in the mare in many cases is not warranted. If fact, the excessive use of such supplements is quite controversial.
The upshot of this information is that breeding an older mare is not something to be taken lightly. Science has provided a lot of help in overcoming some of the pitfalls, but age is a powerful adversary.
About the Author
Les Sellnow is a free-lance writer based near Riverton, Wyo. He specializes in articles on equine research, and operates a ranch where he raises horses and livestock. He has authored several fiction and non-fiction books, including Understanding Equine Lameness and Understanding The Young Horse, published by Eclipse Press and available at www.exclusivelyequine.com or by calling 800/582-5604.
POLL: University Equine Hospitals