It’s common practice at some breeding farms–collecting the drippings from a stallion’s penis after he breeds and dismounts a mare, evaluating the sample to confirm that ejaculation did occur, then placing the sample in the mare. Reinforcement breeding, as the last step of that procedure is called, was found to increase pregnancy rates by up to 11.7% in a study presented at the 2006 American Association of Equine Practitioners Convention.

For the study, Terry Blanchard, DVM, MS, Dipl. ACT, resident veterinarian at a Central Kentucky Thoroughbred farm, evaluated records from all 2005 matings at the farm. These described 2,171 estrous cycles from 1,406 mares that were bred to one of 13 stallions. Initially in the breeding season, reinforcement samples were infused into the uteri immediately after cover in those mares returning on second (or later) cycles of the season. Early results indicated a dramatic advantage to using the procedure with two stallions, so reinforcements were used on all of their subsequent matings for the season.

“The take-home message here is that we had an average per-cycle pregnancy rate increase of 12% in eight of our 13 stallions,” Blanchard told the audience. “The effectiveness of reinforcement was influenced by the number of sperm recovered in the dismount sample that was infused into uterus.”

A rigorous multiple logistic regression statistical model was used to adjust for other factors known to affect fertility, including stallion, mare, cycle, mare age and beginning status (maiden, barren, etc.), foal heat breeding, “doubles” (when a mare is bred twice on a cycle), and month of the year