Deep-voiced stallions are more fertile and more attractive to mares. | © Arnd Bronkhorst

Seeking the perfect mate for your mare? If your mare were searching for herself, she might just ask to hear her suitors whinny. Mares show a clear preference for deep-voiced stallions, researchers in France have found. And the preference isn’t a whim—deep-voiced stallions, it turns out, are more fertile.

Alban Lemasson, PhD, and fellow scientists at the University of Rennes recorded the calls of 15 breeding stallions along with the stallions’ heart rates, hormone levels and reproductive success. They already knew that larger stallions tend to have deeper voices, but this data showed that a lower-pitched call also correlated with a slower heart rate (indicating calmness) and higher fertility. 

Next, 40 mares of varying ages were tested to see how they reacted to the voices. Some were broodmares; others were saddle horses. For the broodmares, the researchers constructed a long enclosure, walled by hay bales stacked high enough that the mares could not see out, with a speaker at each end. Each mare was placed in the middle of the rectangle and released and two stallion calls—one high-pitched, one low—were played simultaneously from opposite sides. The saddle mares were tested in the same way but in a familiar arena.

In repeated trials, the mares turned toward the low-pitched call more often and spent significantly more time in that side of the enclosure. That, the researchers say, shows that mares are attracted to the voices of stallions who are tall, calm and more fertile. Whether mares were in heat or not, their preferences were the same. The researchers say that’s to be expected in horses, since wild bands of females stay with chosen males even when they’re not breeding.

—Elaine Pascoe

This article originally appeared in the September 2015 issue of Practical Horseman.