The decision to manage a subfertile stallion non-conventionally is "based on the condition of farm economics or despair, or more appropriately, the last hope before retiring the stallion," said Irwin K.M. Liu, DVM, PhD, a professor in the Department of Population Health and Reproduction in the University of California, Davis, School of Veterinary Medicine. Liu brought to the table suggestions for managing stallions with declined fertility at the Hagyard Bluegrass Equine Symposium, held Oct. 20-23, 2004, in Lexington, Ky.

"Most of you realize that our understanding and management of subfertile mares has substantially increased," he said. "Assisted reproduction technology has made a significant impact on pregnancy rates in subfertile mares," and has the potential to help subfertile stallions as well.  But not many strategies have helped the subfertile stallion under natural cover conditions and requirements.

Liu explained that testicular degeneration is often--but not always--associated with age and declining pregnancy rates, and it is highly correlated with low sperm concentrations and abnormal sperm pathology. Testicular degeneration varies from stud to stud. "Clearly each management strategy is based on the individual cause of subfertility," said Liu.

The normal sperm of young subfertile stallions  appear to be more fertile than the normal sperm of older subfertile stallions, so managing an older stallion will likely be more intensive.

Stallions can have progressive sperm motility, but show fertility rates that are far below standards--a situation that can be frustrating, but manageable. Liu described several studs whose pregnancy rates with a single breeding prior to the mare's ovulation were unimpressive (10-20%) before they underwent unconventional management. The problems were solved by adjusting the stallions'  breeding schedule: Each stallion bred each mare twice at four- to six- hour intervals in the late afternoon and early evening the day before the mare's anticipated time of ovulation. Liu emphasized that the validity of the suggested strategy was not scientifically documented.

After the first year of management, the stallions' pregnancy rates increased dramatically, although their books of mares were kept small. More frequent matings allow a greater number of normal sperm to be available at the fertilization site, but can deplete the stallion's reserves, so the smaller book might be necessary.

It's important to remember the mare plays a key role in sperm transport, and her reproductive condition will help determine the stud's success. Cilia in the normal mare's uterus and sperm have close interactions and communications that result in only normal sperm reaching the fertilization site. In a chronically infected uterus, adverse conditions prevent healthy sperm from reaching the highly selective oviduct, which selects out sperm with abnormal morphology.

Liu suggested veterinarians should flush the mare's uterus four hours after each mating to a subfertile stallion, if the mare is a persistent accumulator of fluid and debris. "The rationale is based on our current knowledge of sperm transport in the mare," he said. "Billions of sperm are ejaculated in a normal stallion, and only a few hundred gain access to the fertility site. Four hours after mating, one can lavage the uterus of all its contents (to decrease chance of infection that could hamper the pregnancy) without disturbing the pregnancy.

"Once you know you're dealing with a subfertile mare, you know she will always be susceptible to infection after she is bred," he added, so make sure this step is taken.

About the Author

Stephanie L. Church, Editor-in-Chief

Stephanie L. Church, Editor-in-Chief, received a B.A. in Journalism and Equestrian Studies from Averett College in Danville, Virginia. A Pony Club and 4-H graduate, her background is in eventing, and she is schooling her recently retired Thoroughbred racehorse, Happy, toward a career in that discipline. She also enjoys traveling, photography, cycling, and cooking in her free time.

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