Exact Cause of Toxicity Deaths Still Unknown

Researchers at Texas A&M University (TAMU) in College Station, Texas, say they strongly suspect that the pesticide used on feed at nearby Carousel Acres was directly involved in the death of 27 horses. However, the reason for the extreme reaction to the chemical that the farm had used before is still unknown.

 "We did identify phosphine in the stomach cavities of three of the horses," said Richard Adams, DVM, PhD, dean of TAMU's College of Veterinary Medicine. "And since that is the product of the pesticide that the stable was using, the logical conclusion is that it was the cause."

Adams said that results of preliminary tests showed no evidence of anything wrong with the feed itself.

Full test results on the horses, their feed, and bedding are expected next week.

Sunday afternoon, July 16, the Raphels noticed a horse exhibiting clinical signs consistent with heat exhaustion, including sweating and tremors. As they began hosing the horse in an attempt to cool it down, another fell ill.

Adams says that the first 24 horses died within 12 hours of each other. Five were hospitalized at TAMU. Three of those horses died, and veterinarians performed necropsies on the animals.

The two hospitalized horses are in good condition, but Adams says the long-term effects of phosphine exposure on horses are unknown.

 "Some metabolites of the gas can cause liver damage, though we have not seen any evidence of that as yet," Adams says. "We have no way of knowing the actual dose received by those that remain alive."

Catherine Barr, PhD, ABT, a veterinary toxicologist with the Texas Veterinary Diagnostic Laboratory assisted with the testing of the Carousel Acres horses, and explains that aluminum phosphide is used as a fumigant. The solid phosphide produces phosphine as a gas when exposed to water, including water droplets in the air and in the feed itself, Barr says.

However, the phosphine was found in the horse's stomach contents--not the lungs, suggesting that it was ingested rather than inhaled.

The question that remains is why the phosphine did not dissipate within the silo.

Phosphide is a highly controlled substance, due to its high toxicity and necessary safety precautions during use says Barr. A pesticide applicator's license is required for its purchase and use.

The Texas Department of Agriculture's Pesticide Division says that for the treatment of feed, it is necessary to aerate the treated commodities for a minimum of 48 hours prior to feeding it to horses.

Farm owner Bradley Raphel said that Carousel Acres used the same grain treatment once annually for the past eight years, with no previous problems.

"At this point we're just trying to clarify what caused the animals to die," said Raphel.

Of the dead horses, 11 were Peruvian horses that belonged to the Raphel family. Both of their breeding stallions, a top performance horse, broodmares, and foals succumbed.

Bradley says that the 11 horses that were considered to be in "guarded" condition seem to be coming around. 

"People shouldn't panic until (the cause of the deaths is) fully decided," he adds.

Full test results are expected early next week.

For the official TAMU press release see: http://www.thehorse.com/ViewArticle.aspx?ID=7294.

About the Author

Erin Ryder

Erin Ryder is a former news editor of The Horse: Your Guide To Equine Health Care. She owns a portly gray gelding named Duncan and dabbles in several equestrian disciplines, with an emphasis on dressage.

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