How do Equine Dewormers Impact the Environment?

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How do Equine Dewormers Impact the Environment?

The researchers looked at feces-consuming beetles in spring and summer over a two-year period and compared beetles in areas close to horse-riding trails to those in areas closed off to horses.

Photo: Thinkstock

Many veterinarians are encouraging their clients to rethink their deworming protocol, as we now know that too-frequent anthelmintic treatment can lead to drug-resistant parasites. But French scientists have raised another important concern: How do the antiparasitic drugs impact the environment?

In a preliminary study, researchers investigated parasite control practices at equestrian centers neighboring a natural reserve and then looked at how insect populations in the reserve were faring. The team presented their work at the 2014 French Equine Research Day held March 18 in Paris.

Specifically, they looked at feces-consuming beetles in spring and summer over a two-year period. They compared beetles in areas close to horse-riding trails to those in areas closed off to horses. The study was coordinated by Anna Echassoux, PhD, vice coordinator of the Biosphere Reserve of Fontainebleau and Gâtinais, and led by Julien Gasparini, researcher in ecology at Pierre et Marie Curie University in Paris. Brigitte Enriquez, researcher in pharmacotoxicology at National Veterinary school of Alfort, and Jean-Pierre Lumaret and Nassera Kadiri, researchers in entomology at Montpellier University, also contributed to the study.

Echassoux and her team found that in May and June, the dung-eating bugs in the horse-riding areas actually fared better than those without access to horse droppings. However, the opposite was true in July, when the horse-area beetles were fewer in number and had shorter legs than the beetles in non-horse areas.

This could be related to seasonal deworming practices, Gasparini said. Previous studies with sheep and cattle feces have shown that ivermectin and other deworming molecules can negatively affect dung beetles' growth and reproduction. However, specific tests with horse dung would be necessary to make definite conclusions, he said. Furthermore, tests during the larva season would help further explain this phenomenon, he added.

The research team also interviewed 23 neighboring equestrian centers and two equine veterinary clinics, each with about five veterinarians. Fewer than 10% of the horses were dewormed by veterinary prescription under supervision. Furthermore, although nearly three-fourths of the horses were stalled indoors most of the time, they were still dewormed as often as four or more times a year, the investigation revealed.

Echassoux determined that horse owners and riding center managers in the area tended to follow their own parasite control programs without respect for veterinary advice.

“It’s like deworming programs are based on a memory device instead of therapeutic benefit,” Gasparini said. “Four seasons a year, so four times a year, when this is neither necessary nor positive for the environment.”

Veterinarians did appear to be somewhat educated about such medications' harmful effects on the environment, Gasparini said. Many of them warned owners and center managers of the importance of protecting the environment, although the warnings were not often heeded, he added.

“Veterinarians informed us that they advised their clients to pick up the dung from the paddocks or pastures for 48 hours after deworming, but most clients failed to do this,” Gasparini said. “Some of the veterinarians had noted environmental effects of this—mainly that the dung did not decompose as it normally should.”

Research by the Fontainebleau and Gâtinais biosphere reserve on the effects of equine drugs on the environment—for good and for bad—is ongoing.

About the Author

Christa Lesté-Lasserre, MA

Christa Lesté-Lasserre is a freelance writer based in France. A native of Dallas, Texas, Lesté-Lasserre grew up riding Quarter Horses, Appaloosas, and Shetland Ponies. She holds a master’s degree in English, specializing in creative writing, from the University of Mississippi in Oxford and earned a bachelor's in journalism and creative writing with a minor in sciences from Baylor University in Waco, Texas. She currently keeps her two Trakehners at a competition stable east of Paris. Follow Lesté-Lasserre on Twitter @christalestelas.

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