Female sheep found to prefer less dominant males when mating

A team of researchers from Universidad Autónoma del Estrado de Morelos and Universidad de la República, has found that given the choice, female sheep prefer to mate with less domineering males. In their paper published in the journal Applied Animal Behavior Science, the group describe experiments they conducted with male and female sheep and what they learned from them.

Prior research has shown that dominant male domestic sheep tend to mate with more ewes than less dominant males. In addition to gaining greater access to the females, the more dominant males also tend to engage in rougher mating behavior than the less dominant males. Prior research has also shown that some males are so dominant that they cannot physically keep up with their own activities—they run out of sperm. Animal scientists have noted that such strong dominance would put a herd at risk if not for the lack of sperm—they would become inbred and because of that, less robust.

In this new effort, the researchers noticed that when dominant males ran out of sperm, the females tended to gravitate toward those less dominant males. They wondered if that would be the case if the females were able to choose their own mating partner. To find out, they tied up a dominant sheep at one end of a paddock and a more submissive male sheep at the other end. They then let in seven ewes that were in estrous and let them choose which of the males they wanted as their mating partner. They repeated the exercise multiple times with different groups of ewes.

In watching the action, the researchers found that in a quarter of the exercises, none of the females chose the dominant male at all. In instances where some of the ewes did choose to mate with the more dominate male, there were fewer mounts and many fewer mates than with the less dominant males. They also found that the ewes appeared to enjoy the company of the less dominant male. They spent on average triple the amount of time in his company than the more dominant male—and spent on average twice as long mating with him.

The researchers suggest evolution has likely programed ewes to go for the less dominant males, to prevent inbreeding. But it also seems that they simply preferred a gentler approach.

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