Random FAQ: Can Horses Pick Up Worms from Eating Hay?

FOR IMMEDIATE RELEASE — APRIL 12, 2012 — Recently a client asked if it’s possible for a horse to pick up worm larvae or worms from eating hay, and if so, even if larvae are dead, could they cause a parasite problem? Upon further discussion, she mentioned that she was aware of the serious problems that could be caused by dead blister beetles in hay (every horse owner should know about blister beetles—see the University of Illinois Extension article for more information) and wondered if it was possible for dead worm larvae to pose a similar but far less serious health threat. The short answer “No.”

On March 7, 2012, parasitologist Dr. Martin K Nielsen commented on the likelihood of parasite acquisition from hay onHorsetalk.co.nz in response to a question from another horse owner who was also concerned about the same issue.

Horses cannot pick up larvae or worms from hay. Horses must be grazing in a pasture where eggs from horse droppings hatch, become larvae, and climb the grass stalk where they will be devoured by a grazing horse. Once ingested, the worm life cycle begins again. In the unlikely event that there are dead worms in the hay, they will not present a problem.

In theory, it is possible for hay that is harvested from fields where young horses were recently pastured to contain round worm eggs. Additionally, some articles have suggested that where horses have been recently pastured, soil-dwelling oribatid mites might possibly find tapeworm eggs to eat, which then develop into infective larvae. A 2008 Tapeworm Special Report (PDF) sponsored by Pfizer Animal Health noted that “the presence of the types of oribatid mites associated with the equine tapeworm life cycle has not been proven in hay, straw, or wood products, or in aquatic environment.” So, these two scenarios are unlikely to occur.

Horsemen’s Laboratory owner Dr. John Byrd has extensive experience with racing and breeding horses and oversees Westbrook Boarding Stable. He created Horsemen’s Laboratory in 1992 so that horse owners could better evaluate their worm control programs and make informed decisions about deworming their horses.

Visit www.horsemenslab.com to learn more about Horsemen’s Laboratory and parasites, to sign up for the monthly newsletter, and to order testing kits. You can also order kits by calling 1-800-544-0599.

If you have questions specific to your barn, pastures, or testing program contact Dr. John Byrd by:

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