Not Always the Alphas: Female Sheep Prefer Less Dominant Males as Mates

A new study suggests that when given the chance to choose a partner, female sheep would prefer to mate with the less domineering males.

Researchers from Universidad Autónoma del Estado de Morelos in Mexico and Universidad de la República in Uruguay conducted experiments with male and female sheep. They present their findings in the article "Ewes prefer subordinate rather than dominant rams as sexual partners," set to appear in the May issue of the Applied Animal Behaviour Science journal.

Desert bighorn rams clash horns to establish power and dominance

(Photo: Photo by David McNew/Getty Images)

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A Natural Limit to the Herd

Previous studies have established how the dominant male in domestic sheep populations tends to mate with more females compared to the less dominant one. In natural setups where rams and ewes interact freely, the more dominant male usually performs the most number of mounts and mating with the females in the herd. While the more dominant ones have greater access to the female sheep, they also tend to engage in rougher mating behavior.

These dominant male sheep are also known to be too dominant that they cannot keep up with their mating loads and run out of sperm. Zoologists believe that this excessive dominance would be a threat to the herd if they had more sperm because of the monopoly of mating, increasing inbreeding, and reducing the quality of the new generations.

In the latest study, researchers noted that when the dominant rams ran out of sperm, females tend to search for the less dominant rams as an alternative. It led researchers to inquire whether these ewes would still choose the less dominant male, given the opportunity to do so.

Allowing the Females to Choose their Mate

To test their proposal, researchers tied up a dominant sheep to one end of a paddock and a less dominant one at the other end. Seven female sheep in estrous were allowed in, letting them choose who to mate with without active interference from the rams. Researchers then repeated the experiment a few more times, with each iteration using a different set of ewes.

Upon observing the ewes, researchers discovered that in about a fourth of the experiments done, none of the females chose the dominant male. In other instances where some ewes preferred the more dominant male, researchers noted fewer mounts and fewer mates compared to the pairings with the less dominant males. Additionally, ewes apparently enjoyed the company of the more submissive ram. Females tend to spend triple the amount of time, on average, with the less dominant male compared to the more dominant one - and twice more on average mating with the less dominant one.

To explain this behavior, researchers suggest that evolution has programmed female sheep to turn to less dominant males in order to reduce inbreeding in the herd. Another possible reason is that the females prefer a gentler approach to mating - one that is possible with the less dominant male partners.