Semen Optimization Increases Fertility of Subfertile Stallions

Veterinarians at The Georgia and Philip Hofmann Research Center for Animal Reproduction at Penn Vet's New Bolton Center in Kennett Square, Pa., have enjoyed notable success with semen optimization processing techniques. These techniques are valuable tools in equine reproduction for select stallions that might need some level of assistance with the quality of their semen. According to Regina Turner VMD, PhD, Dipl. ACT, "At New Bolton Center, we are applying and modifying different techniques, tailoring the processes to meet the needs of individual stallions. The great success that we have seen using this approach with a small group of stallions this year has made a huge difference in their ability to reproduce."

So far this year, Turner and Audrey Kelleman, DVM, Dipl. ACT, have used a different customized semen optimization process with each of four stallions, all with very promising results. With each individual, semen is collected and analyzed, and the veterinarians work with different processes until they find the ideal combination of processes for that stallion.

"Stallion A," for instance, is an older, retired performance horse who was a star in his day. The stallion has been subfertile since the early '90s and had sired no offspring for the past 10 years. Though his offspring have always been very valuable, the poor quality of his semen caused his owners to all but give up breeding him. When he came in to New Bolton Center to have a sample of semen frozen in the hopes that developing procedures could make his poor quality semen usable in the future, it was recommended that his owners also consider semen optimization.

The stallion's semen displayed not only poor sperm motility (the ability of the sperm to move in a forward motion), but a severe lack of morphologically (through a microscope) normal sperm, a condition that can be caused by age, injury, illness, or genetics. After collection, semen was spun in a centrifuge with a silane-coated silica gradient that separates sperm based on buoyancy. Because normal and abnormal shaped sperm have different buoyancy, veterinarians were able to filter out many of the abnormal sperm. While the numbers of sperm that were recovered were low, they were mostly normal. To date, out of three mares bred, one mare, and possibly a second, has become pregnant from the sperm. "At the very least," says Turner, "we have a 33% success rate from a stallion that had been essentially sterile for over a decade. That's pretty terrific."

"Stallion B" came to New Bolton Center for an orthopedic procedure that left him temporarily unable to mount a dummy mare. This middle-aged stallion's success in the conformation ring made him widely prized for breeding. While the team at New Bolton Center quickly trained him to ejaculate without a dummy, the semen's motility after being cooled for shipping was poor, and pregnancy rates had dropped to almost nothing. The problem was determined to be with the seminal plasma (fluid in semen). In this case, the horse’s semen was spun with a thick, liquid pad at the bottom of a test tube. This procedure allows for the separation of sperm from the plasma, but with less chance of damage to the sperm. Seminal plasma was aspirated off and replaced with semen extender, a commercially available formula based on milk, glucose, and antimicrobials. The longevity of Stallion B’s semen is now very good, and pregnancy rates are back up over 70%.

Semen optimization is just one of the reproductive services offered at the Hofmann Center. Stallions are a specialty of the center, and its reproductive specialists have extensive experience with male infertility and behavior problems. Services offered range from routine procedures such as stallion training, fertility evaluations, semen collection for transport, semen cryopreservation, and contagious disease screening to advanced procedures such as embryo transfer and oocyte transfer for the mare, low dose artificial insemination, evaluation and treatment of behavior problems, and advanced semen processing.

For more information about any of these services, contact the Hofmann Center at 610/925-6364.

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