It’s no secret: We’re not dealing with the same parasites in horses’ intestines as we were decades ago. As parasites adapt to their surroundings—sometimes becoming resistant to treatment—they can become more difficult to eliminate, meaning researchers are seeking new ways to effectively manage these tiny terrors.

To better understand the situation, one research team recently took a close look at wild horses and their parasite burdens.

“Studying wild horses allows us to better understand the interaction between horses and their parasites without human intervention and especially without the use of deworming treatment,” said Lucie Debeffe, PhD, of the Department of Biology at the University of Saskatchewan, in Saskatoon, Canada. “Because parasites are evolving and adapting (sometimes making them resistant to treatment), it is of a primary interest to understand how wild populations of horses interact with their parasites.”

In their recent study, Debeffe and her colleagues studied 477 feral horses on Sable Island, in Nova Scotia, Canada. They found that, for the most part, horses coped well with parasite loads, although the heavier the load, the lower the horse’s body condition score