Call it the “Barry White Effect.” A study from the University of Rennes 1 in France shows that mares are more attracted to stallions who have deeper whinnies—and those stallions are generally more fertile.

The researchers recorded the whinnies of 15 breeding stallions of various ages and collected information on their semen characteristics, breeding records and testosterone levels. The recorded whinnies were then played for various mares and their reactions were observed.

Click here to read about research into what different pitches of whinnies may mean.

The researchers report that mares paid more attention to the lower-pitched whinnies, spending more time near the loudspeakers from which they were broadcast, even as higher-pitched calls were played concurrently on an opposite speaker. Mares seemed to prefer the deeper-voiced vocalizations regardless of whether they were in season.

What’s more, the researchers discovered that a higher percentage of embryos produced using semen from stallions with the deeper whinnies survived compared to embryos sired by stallions with higher-pitched vocalizations.

Reference: “Mares prefer the voices of highly fertile stallions,” PLOS ONE, February 2015

This article first appeared in EQUUS issue #456

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