Written by Benjamin Espy, DVM
Many horse owners feed alfalfa hay to supplement their horse and is a very efficient source of protein and calcium. Alfalfa hay requires very specific growing conditions and is primarily harvested in the western United States. Even if you are using alfalfa that has been harvested months or years previously, your horse is still at risk for blister beetle toxicity.
The blister beetle (Epicauta) is highly toxic to sheep and cattle, but primarily to horses. As little as four (4) to six (6) grams of blister beetles can be deadly to an 1100 lb. horse. Blister beetles swarm in alfalfa fields and are drawn into bales by accident. Even small parts of these beetles are toxic to a horse. Whole insects need not be present to be dangerous.