April 2007
From the State Vet's Office

Blister Beetle Poisoning Associated With Alfalfa Hay

by Dr. Tony Frazier

The winter of 2006-2007 has been one of the worst in many, many years when it comes to the supply and quality of hay available. As a consequence of the drought last summer, many livestock producers and horse owners have had to cull or liquidate animals they would rather have kept if they had anything to feed them.

Because of the design of the digestive tracts of both the cow and the horse, forage intake at some level is necessary. With that in mind, along with the hay shortage, people have frequently been forced to buy hay from unfamiliar sources and certainly without any known history of how the hay was produced, harvested, or even where it came from. This scenario became very apparent in February when a handful of Alabama horses died and another handful became ill from ingesting blister beetles that had been harvested in alfalfa hay.

Information began to surface about the third week of February that some horses in Alabama had died from blister beetle poisoning (cantharidin toxicity) associated with eating alfalfa hay infested with blister beetles at the time of harvest. A conversation with the veterinarian who attended these horses confirmed that the diagnosis had been made based upon levels of cantharidin found in the urine of the first horse that died as well as a history feeding alfalfa hay. Some blister beetles had also been collected from some of the remaining hay that was being fed. That information led to a full scale media blitz from various organizations (including the Alabama Department of Agriculture and Industries) and media outlets to make horse owners aware of the possible threat of blister beetle poisoning associated with feeding alfalfa hay. Also some dried beetles were found in the hay.

While there is reason to be cautious when feeding alfalfa to horses, it is not something to be thought of as too dangerous to feed to horses. There are, however, certain precautions that should be taken to minimize the chances of blister beetles being in the alfalfa. First, if at all possible, know the source of the hay. Reputable alfalfa producers are very aware of the blister beetle danger and check for swarms of the beetles before harvesting the hay. Because the beetles only stay on small areas of the field for a short time, reputable alfalfa producers will delay harvest until the beetles are gone.

Second, if possible, find out when the hay was harvested. Usually the first cutting is desirable for horses for two reasons. Number one: blister beetles are not usually active before June. And number two: the alfalfa has not yet bloomed. It seems that blister beetles are attracted to blooms on the alfalfa and even weeds in the hay field that may be blooming. It is also good to know if a hay conditioner was used because that process could crush the beetles into small enough pieces that they would not be detectable. However, if sickle mowers or the modern circular hay mowers are used, the beetles will usually abandon the cut hay to find moisture and food somewhere else. Finally, the least reliable practice to stack the deck against blister beetles is to inspect the hay. The dried beetles may be detectable in the hay, but they may not be.

If horses or other livestock ingest enough of the cantharidin-producing beetles, the signs of illness are dose related. Early or mild signs may be that of colic which can be induced by the toxin. Other signs include depression and urinary tract problems such as straining to urinate or frequent urination. If enough of the toxin is ingested to cause severe cardiovascular problems, death can occur within a few hours. These signs are not diagnostic for the toxin; neither are laboratory tests other than finding the toxin in blood or urine. However, these signs accompanied by a history of feeding alfalfa hay, cantharidin toxicity should be a strong consideration.

There is no specific antidote to the toxin. Treatment of cantharidin affected horses should be treated symptomatically. The hay should be closely examined and removed. Mineral oil should be given via stomach tube with or without activated charcoal to slow the absorption and speed the elimination of the toxin. Fluids should be given to correct dehydration and to increase flushing of the kidneys. Anti-inflammatories and analgesics are also indicated.

In a year that has seen the worst hay shortages in a long time, we are not always presented with easy choices of how to keep our livestock nourished and completely side-step possible danger associated with various feed sources. Still the best tool to have in our toolbox is to be educated and informed about what we are feeding our animals. Any questions should be directed to your veterinarian or extension personnel such as the regional livestock and forage specialists.