How to Select and Prepare a Stimulus Mare

When evaluating the mare's response to stallions, Whitesell said they present stallions of various ages, experience, breeds, and temperaments.

Photo: Courtesy Dr. Sue McDonnell/Havemeyer Equine Behavior Lab at Penn Vet's New Bolton Center

Sometimes even the most eager stallion requires a little motivation when it comes to semen collection for artificial insemination. Thus, most breeding facilities employ the help of a live "stimulus" mare to put him in the mood. Not just any mare, however, will do for all stallions.

Kristina Janson Whitesell, DVM, a reproduction resident and research fellow in the Havemeyer Equine Behavior Program at the University of Pennsylvania's New Bolton Center in Kennett Square, described the ideal stimulus mare candidate and how to prepare her at the 2013 American Association of Equine Practitioners' Convention, held Dec. 7-11, in Nashville, Tenn.

"A stimulus/mount mare that is an easy keeper, sound, and reliably attractive and receptive to most stallions, as well as comfortable with her work and easy to handle, is invaluable to a breeding facility," said Whitesell.

"A cycling mare in natural estrus close to ovulation is typically the most stimulating to stallions," she said. And on farms with large herds of mares from which to select on any given day, a naturally cycling mare is often a good choice. But for many facilities the choice is to prepare one or more ovariectomized (with ovaries removed) mares that can be used year-round as a stimulus/mount mare for semen collection.

To determine whether a mare will be reliably stimulating, receptive, and safe for the job at hand, Whitesell and her colleagues run each candidate through a detailed evaluation process. They consider mares that are sound, healthy, not too old, have a good temperament, and demonstrate estrus. If a mare meets these criteria, Whitesell then uses a behavior evaluation checklist to assess the horse's comfort and compliance with the collection process as well as her response to different stallions, and the different stallions' response to her.

She said ideal stimulus mares should exhibit:

  • Tolerance and comfort with application of a twitch, breeding cape, hobbles, breeding boots, and tail wrap;
  • Receptive responses to stallions with and without a twitch;
  • Ease and comfort loading and standing for long periods in stocks, as well as unloading from them;
  • An absence of nonreceptive responses such as striking, squealing, biting, kicking, rearing, moving away, etc.; and
  • Tolerance of being mounted.

When evaluating the mare's response to stallions, Whitesell said they present stallions of various ages, experience, breeds, and temperaments and note specific issues the mare exhibits, such as leaning into the stallion or pushing against the dummy.

"Because we are a teaching facility with day-to-day variation in the handling team, we also try to assess the candidate's cooperation and comfort with handlers of various skill levels and handling styles," she said. "A particular concern is to identify behavior that would pose safety threats for less experienced handlers."

Once Whitesell's clinic selects a mare, they perform an ovariectomy followed by estrogen treatment to induce and maintain estrus.

In conclusion, Whitesell said, "organized and systematic behavior evaluation specific to your clinic's protocols before selection will reveal undesirable behaviors that may prove unsafe in the semen collection environment or may complicate or prevent successful semen collection.

"But with careful selection and preparation, a stimulus mare can offer many years of service and be an integral member of a reproductive service team," Whitesell said.

About the Author

Alexandra Beckstett, The Horse Managing Editor

Alexandra Beckstett, Managing Editor of The Horse and a native of Houston, Texas, is a lifelong horse owner who has shown successfully on the national hunter/jumper circuit and dabbled in hunter breeding. After graduating from Duke University, she joined Blood-Horse Publications as Assistant Editor of its book division, Eclipse Press, before joining The Horse.

Stay on top of the most recent Horse Health news with FREE weekly newsletters from Learn More