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Study: Gelding wild horses is not easy solution to overpopulation

Wild horses
Colorado State University
Wild horses

News brief

With about 82,000 wild horses and burros on public lands, researchers are looking for options to address the overpopulation.

A study released recently by the U.S. Geological Survey and Colorado State University shows gelding wild horses didn’t really affect their behavior – or have a long-term impact on herd size.

CSU Researcher Sarah King, who led the behavioral aspect of the study, says they gelded 42% of the stallions in the herd in the Conger Herd Management Area in Utah.

“We really thought that it would maybe have big impacts on their behavior and they would just act like bachelor male horses,” said King, part of the university’s Natural Resources Ecology Laboratory. “Surprisingly, we found it had almost no effect on their behavior at all.”

She says some stallions have a harem of mares, and the gelded harem stallions stayed with their mares. They still defended the harem, fought and showed reproductive behavior.

But by the end of the four-year study, almost all of the harems had disbanded.

“Again, [it’s] one of these questions that everybody is like, ‘We castrate males to control their behavior, so their behavior is controlled’ without actually looking at it,” King said.

Though many domesticated stallions are gelded, she says there isn’t a lot of research on how it impacts their herd dynamics.

In the first year after the surgeries, the herd’s birth rate decreased. But it bounced back after a couple years.

King says this could be due to the number of stallions gelded in the population, mares mating with non-gelded stallions outside their harem or bachelor stallions sneaking in. King thinks gelding may have a larger impact on overpopulation if it’s coupled with female fertility control. Next, the team will look at DNA data collected from the herd to better understand the herd’s dynamics and foaling rate.

“Understanding the behavior of animals is often undervalued in how it can be used to manage animals and also to conserve them,” King said in a news release. “Once we understand how and why animals are using the landscape, it can really affect management decisions and what will affect fertility and reproductive behavior.”

This story was produced by the Mountain West News Bureau, a collaboration between Wyoming Public Media, Nevada Public Radio, Boise State Public Radio in Idaho, KUNR in Nevada, the O'Connor Center for the Rocky Mountain West in Montana, KUNC in Colorado, KUNM in New Mexico, with support from affiliate stations across the region. Funding for the Mountain West News Bureau is provided in part by the Corporation for Public Broadcasting.

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