Processing High- and Low-Quality Semen in Horses (AAEP 2011)

Processing High- and Low-Quality Semen in Horses (AAEP 2011)

When faced with a stallion that produces a low-quality ejaculate, meaning it contains low numbers of spermatozoa that do not move well or do not tolerate cooling, it's important to take special steps to maximize the chances of impregnating the mare.

Photo: Anne M. Eberhardt/The Horse

All you need is one microscopic DNA-containing cell with a long tail swimming madly to meet up with an egg. How difficult can it be? Plenty, according to Etta Bradecamp, DVM, who puts the odds at about one in a billion for a pregnancy arising from just one sperm and one egg. Bradecamp, a practitioner with Rood & Riddle Equine Hospital, in Lexington, Ky., described the challenges of processing semen for shipping at the 2011 American Association of Equine Practitioners convention, held Nov. 18-22 in San Antonio, Texas.

"The use of cooled-shipped semen to inseminate mares is widespread in the industry, and not all spermatozoa tolerate cooling," she explained. "In addition, not all ejaculates, even from a 'proven' stallion, are the same and need to be constantly evaluated to ensure that no less than one billion sperm cells capable of progressive motion are shipped in each order."

In addition to the challenges associated with cooling and shipping the sperm and inseminating the mare, some stallions simply do not produce a high-quality ejaculate in the first place. "Stallions are often selected based on attributes such as physique or athleticism, not their sperm quality," said Bradecamp.

Thus, when faced with a stallion that produces a low-quality ejaculate, meaning it contains low numbers of spermatozoa that do not move well or do not tolerate cooling, it's important to take special steps to maximize the chances of impregnating the recipient mare.

Among these steps are the following:

  • Handle the sperm carefully after collection to avoid "shock" (i.e., a loss of motility and general viability);
  • Keep the sample away from light;
  • Dilute the sample with extender (a milk-based liquid product that improves sperm survival during cooling) to achieve a final sperm concentration of 25-50 million sperm/mL;
  • The stallion's own seminal fluid, a normal part of the ejaculate, can be toxic to the sperm. Consider centrifuging the sample (spinning it in test tubes at very high speeds) to separate the spermatozoa from the seminal fluid. Centrifuging will also concentrate the spermatozoa, which then can be mixed with extender to achieve a higher number of sperm/mL;
  • Use special "centrifugation cushions" to protect the cells during their traumatic spinning session to maximize sperm viability.

"The best product is produced when the ejaculate is packaged at the correct concentration and dilution ratio in an appropriate extender, and always ship at least one billion viable and progressively motile spermatozoa every time," concluded Bradecamp. "Remember to treat each stallion as an individual and continually test the ejaculate to determine if any changes need to be made during the process to improve semen quality."

About the Author

Stacey Oke, DVM, MSc

Stacey Oke, MSc, DVM, is a practicing veterinarian and freelance medical writer and editor. She is interested in both large and small animals, as well as complementary and alternative medicine. Since 2005, she's worked as a research consultant for nutritional supplement companies, assisted physicians and veterinarians in publishing research articles and textbooks, and written for a number of educational magazines and websites.

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