Life can be a little tough when you’re a low-ranking horse. Not only do you get “second pickings” when sharing food or interrupted more often during rest, but new research suggests you might also have a higher intestinal parasite burden.

“As we strive to find ways to reduce parasite resistance to dewormer medications, we need to be able to recognize and target the individuals that are more likely to have parasites and need deworming medication,” said Léa Briard, PhD, of the University of Strasbourg, in France.

“Our study is the first to show that dominance rank is related to parasite burdens and that lower-ranking individuals tend to have more intestinal parasites,” she said. Briard presented her work at the 42nd French Equine Research Day, held March 17 in Paris.

In her pioneering, preliminary study, Briard and colleagues followed a herd of 13 horses and ponies, aged 4 to 27 years. None of the animals had ever been treated with anthelmintic medications (dewormers). The scientists observed the horses for hierarchical rank six hours a day, six days a week, for three months. They also tested the animals regularly for intestinal parasite loads, collecting feces for analysis twice a week.

Briard said the team found a distinct link between dominance rank and parasite load.

“The more dominant an individual was, the lower that animal’s parasite burden,” she said of the horses in her study.

It’s possible that the stress of being lower-ranked could lower the horse’s immunity to the parasites, but that’s unlikely given that recent studies have shown