Feed contaminated with a pesticide used to kill weevils is likely responsible for the deaths of 27 horses in July 2006 on a ranch in College Station, Texas.

Several horses at Carousel Acres Equestrian Center and Stable first became ill July 16. Twenty-four died within a day and about 20 more became ill. Five were admitted for treatment to the veterinary hospital at Texas A&M University.

“The horses showed signs of a central nervous disorder, with staggering, muscle fasciculation, ataxia and excessive sweating,” says H. Richard Adams, DVM, PhD, dean of Texas A&M’s College of Veterinary Medicine and Biomechanical Sciences. “The fact that so many animals got horribly sick so quickly was suggestive of an environmental factor. The owner acknowledged using a pesticide on the feed the night before the animals got ill.” Necropsies of three horses revealed the presence of phosphine gas, a by-product of a pesticide commonly used to treat bulk feed stored in silos.

Carousel Acres owner Brad Raphel, who breeds Peruvian Pasos, says he had used the agent several times before with no adverse effects. “It’s a pelleted product that breaks down into a gas and starves the weevil of oxygen. But the mystery lies in how this could kill a horse. Hypothetically, you could put far more pellets in a one-ton canister and not do the animals harm. It just doesn’t make sense.” Raphel is awaiting test results on feed samples from the state department of agriculture.

“All of our stallions and best mares” were lost, Raphel says, as well as more than a dozen boarded horses. In the aftermath of the incident, several individuals and organizations have donated money and supplies. Some have offered horses to help the facility get back on its feet.

This article originally appeared in the October 2006 issue of EQUUS magazine.