Danger in the Manger: Blister Beetle Toxins Kill Six North Carolina Horses

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Credit: NCDA&CS image Six horses are dead in North Carolina. Their deaths have been linked to blister beetle poisoning in alfalfa hay shipped east from Kansas.

Credit: NCDA&CS image Six horses are dead in North Carolina. Their deaths have been linked to blister beetle poisoning in alfalfa hay shipped east from Kansas.

This is not supposed to happen, but every once in a while, it does. The familiar smell of a fresh bale of alfalfa hay can carry the dangerous risk of cantharidin poisoning to horses. It happened last week in North Carolina, and six horses are dead.

Cantharidin is a toxin found in insects known as blister beetles. There are several types of blister beetles, but the risk of poisoning is not directly linked to the presence of actual insects in the hay. The beetles release the toxin when stressed, as they would be when disrupted by farm machinery. Crushing the insects themselves would also release the toxin into the hay, but there is really no way to guarantee that hay is free of blister beetle poisoning just by visual inspection.

Most farm animals are affected by blister beetle infestation in alfalfa hay, but the toxin is deadly to horses.

The beetles are typically found in the midwest, and might have been completely unknown to North Carolina horseowners. Officials with the North Carolina Department of Agriculture and Consumer Services (NCDA&CS) investigated the deaths and traced the cause to a single load of hay from Kansas that was sold by one feed dealer; Murphy Farm Hay and Feed in Louisburg, North Carolina received the load on August 11, 2015.

Bales from this load were further distributed to another retailer, Jones Farm Hay and Feed in Middlesex, North Carolina.

NCDA&CS issued a press release to alert horse owners in the state of the possible danger in their hay. They noted that the bales from the load of hay were bound with a reddish-orange twine and advised customers who purchased alfalfa hay, bound with a reddish-orange twine, bought on or after August 11 from either location to stop using it immediately and return it to the location where purchased.

“Our feed inspectors have identified much of the hay sold from these locations thanks to the cooperation of both feed stores,” said Agriculture Commissioner Steve Troxler. “We are continuing to reach out to all customers that may have purchased hay from either store as we attempt to account for the distribution of the entire load.”

The load of hay, containing about 500 bales, was found to be contaminated with the striped blister beetle. 

NCDA&CS advises horse owners to monitor their animals and contact their veterinarians if any of these signs are observed: inflammation, colic, straining, elevated temperature, depression, blood in the urine, increased heart rate and respiration, dehydration, sweating, diarrhea and death.

North Carolina Equine Extension has posted a supplemental information page for horse owners about blister beetles and cantharidin poisoning.

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