Problem Breeder Mare

Getting mares in foal sometimes can be a tall task.

What do veterinarians involved with reproduction have in common with the fictitious Sherlock Holmes? Both play the role of detective in solving mysteries. With Arthur Conan Doyle's legendary character, the mystery generally involved identifying the perpetrator of a crime. With the reproductive veterinarian, the mystery often involves determining why a mare fails to come into estrus, or why she doesn't conceive when she does.

Complicating matters for the veterinary sleuth is that there often is more than one reason the mare's reproductive system isn't functioning as it should. Normally, the mare will provide some clues as to why this is so, but the veterinarian must follow through with an exhaustive examination of the evidence at hand.

One such case treated by Elizabeth (Lisa) Metcalf, DVM, MS, Dipl. ACT, of Sherwood, Ore., a specialist in equine reproduction, involves a senior Hanoverian mare in Germany that had produced foals after an illustrious show career, then appeared to have "shut down." It was April, well into breeding season, and she simply was not cycling.

Metcalf will tell us how she examined the evidence presented by the mare and what steps she took to solve the problem.

Mare's History

First, Metcalf studied the mare's history. She was 24 years of age and had produced 10 foals since retirement from competition at 12. She was a valuable producer. Her 12-year-old daughter won an Olympic Gold Medal. She was last bred the previous November; two embryos had been flushed and transferred into recipient mares. She was in her second year as an embryo donor.

She had carried a foal to term four years previously. She had been under lights since Jan. 1 of the current year to manipulate her estrous cycle.

Next came a determination of the mare's body condition. Body condition scores generally range from 1 to 9, with 1 being emaciated and 9 being obese. The goal, says Metcalf, is for the body condition score at the time of breeding to range between 4 and 6, depending on the breed of horse. There also should be indications that the mare is on an increasing nutritional plane, which would mimic natural breeding conditions in the spring when nutritious grass makes its appearance. The mare in question was in the appropriate condition.

Next to be examined was the hair coat. The condition of the hair coat can provide telling clues, Metcalf says. If the mare has shed out, or if she is continuing to shed, a pituitary abnormality (which can introduce reproductive problems) is less likely.

Hands-On Exam

Then came a breeding soundness examination via transrectal palpation and ultrasound. The exam revealed a "doughy uterus," well over the brim of the pelvis, with poor tone. Transrectal ultrasound did not reveal intraluminal fluid or significant problems with the ovaries. There were few follicular structures (vesicles in the ovary containing developing eggs).

A vaginal examination with a speculum, plus digital examination, revealed that the cervix was within normal limits, but it had poor tone. Further endometrial examination failed to reveal any serious abnormalities.

The evidence at this point indicated the mare did not have serious problems with her reproductive system, other than those produced by the aging process--she simply wasn't cycling.

It appeared reasonable to Metcalf and a colleague with whom she was working that, based on the evidence, the mare's reproductive system needed a "jump-start." First, however, one final bit of evidence, or lack of it, had to be considered. It was time to run a hormone profile on her to rule out, for example, the retention of endometrial cups (small structures that form in the uterus around Day 35 of pregnancy--they secrete a hormone that helps the mare retain pregnancy), and to determine the possible presence of luteal tissue (forms when the ovarian follicle converts to a corpeus luteum after discharging an egg) capable of responding to prostaglandin.

Based on the evidence before them, Metcalf and her colleague decided on a therapeutic approach with hormones to get the mare's reproductive system functioning again. She remained under lights for 16 hours per day and was administered progesterone and estradiol, aimed at priming the hypothalamus and pituitary gland for normal estrous cycles. After 10 days of this therapy, the mare was administered twice daily injections of eFSH (equine follicle-stimulating hormone) to stimulate follicular development.

It didn't work. She still wasn't cycling.

Undaunted, the veterinarians launched a second 10-day hormonal therapy approach--again administering progesterone and estradiol, followed by eFSH. Although this protocol does not necessarily result in an increase in the number of embryos in a cycling mare compared to eFSH alone, Metcalf says, the progesterone and estradiol might help transition a mare out of winter anestrus (the sexually inactive period between reproductive cycles).

This time it worked. A follicle developed and, aided by administration of an ovulatory induction agent, the mare ovulated. The oocyte was joined by a spermatozoa that had been sent on its way via artificial insemination. An embryo was recovered and successfully transferred to a recipient.

"We were lucky in many ways," Metcalf says. "Some of that luck may have revolved around allowing her an adequate anestrus period (from November to April). Mares have not evolved to be cycling year-round. They are seasonal breeders. And, of course, old mares are more likely to fail to ovulate and to produce poorer quality oocytes and embryos than young mares."

About the Author

Les Sellnow

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.

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