Blister Beetles in Horse's Alfalfa Cause Severe GI Irritation and Colic

Date Published: 06/08/2009

In periods of dry weather, coastal Bermuda hay that many Texans and others in coastal areas feed their horses sells at a premium price. In some cases, it is not even available so many people in Texas start feeding alfalfa hay trucked in from other states. One of the major problems with alfalfa hay is that blister beetles can be bailed up in the hay. Much of the alfalfa grown in Texas has blister beetles in it and that is one reason many people get their alfalfa from other states. Blister beetles get their common name from the irritating reaction of their body fluids with animal skin or membranes due to a chemical in their bodies called cantharidin. Blister beetles are found throughout the U.S. but are common west of the Mississippi.

The adult beetles emerge in May and June and feed on the leaves of the alfalfa plant. The blooms of the alfalfa attract large numbers of beetles; cutting hay before blooming decreases the number of beetles. Dr. Chris Sansome of the Texas Agricultural Extension Service indicates most of the beetles are located within 50 yards of the field border and if large concentrations are found, harvesting should be delayed. Killing the beetles with an insecticide is really not helpful as the dead beetles are still toxic and many will still be in the hay. Although the beetles can be seen in the hay, it would take a long time to look through that much hay. It is therefore recommended to know your alfalfa supplier and be sure they are familiar with the beetles. At this time there is no sampling method that can determine toxicity in cured hay. Blister beetles cause severe gastrointestinal irritation and colic in horses and in many cases can lead to death.

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