Stallion Collection Schedules Affect Mare Pregnancy Rates
Artificial insemination can be a management-intensive and expensive endeavor for mare owners. They must time the mare’s ovulation precisely with the availability of good-quality semen. Therefore, owners are often at the mercy of when their desired stallion is collected and, if dealing with shipped semen, when that semen arrives.

Lisa Metcalf, MS, DVM, Dipl. ACT, owner of Honahlee PC, a breeding facility in Sherwood, Oregon, recently looked at how collection and insemination schedules affect pregnancy rates in mares bred using fresh or cooled semen. She shared her findings at the 2017 American Association of Equine Practitioners convention, held Nov. 17-21, in San Antonio, Texas.

Breeding stallion collection schedules can vary widely, said Metcalf. Many are collected every other day, while others are collected daily, weekly, Monday-Wednesday-Friday, or between horse shows. The reason for this variation, she said, can be stallion- or staff-dependent.

This poses a problem for mare owners working with a limited breeding window due to the short lifespan of the mare’s oocyte and the stallion’s sperm.

In her study, Metcalf compared pregnancy rates when stallions were available for daily collection to rates from a prior study in which stallions were on an every-other-day schedule and analyzed the differences between on-farm (fresh) and shipped semen (cooled) insemination pregnancy rates. In the current study, she documented 417 mare cycles, inseminating mares with fresh semen during 73 of the cycles and shipped semen during 344. All were bred with semen containing at least 500 million motile sperm (the gold standard) from one of four proven stallions 24 hours after induced ovulation. She performed an ultrasound exam to confirm pregnancy 14 to 20 days later.

“There was a significant difference between on-farm (75%) versus shipped semen (63%) pregnancy rates,” she said. “And pregnancy rate significantly increased for both on-farm and shipped semen inseminations when stallions were available daily.”

This confirms that the duration of time from collection to insemination significantly affects pregnancy rates, she said.

Metcalf offered recommendations for breeders and their veterinarians to maximize their chances of achieving a successful pregnancy:

  • Know the stallion’s contract terms (how frequently he is available, how many collections are permitted, etc.);
  • Communicate with mare owners and stallion managers;
  • Consider using same-day delivery for semen;
  • Find a reliable courier to transport semen; and
  • Set a standard for stallions to be available during breeding season seven days a week.