Deworming Horses: Less is More
Check to see if your dewormers are working by running two egg counts: one at the time of deworming and another one about 14 days later. | Photo: Michelle N. Anderson
Q. Last spring my veterinarian requested her clients stop deworming their horses. We now do no deworming and have her perform two fecal egg counts per year—one in the spring and one in the fall. I’m concerned this isn’t comprehensive. I own two horses and one is a 31-year-old senior with recurring uveitis and Cushing’s. Is this program of not deworming okay for my horses?

—Heather, Pittsburg, Pa.

A. Your veterinarian has a point: There’s no doubt that the majority of horses in North America are over-dewormed, and the large majority of adult horses require very little deworming if at all.

Although all horses get internal parasites, the risks of actual disease caused by these are very low in adult horses. Foals and yearlings are more susceptible to infection and hence more at risk. However, in our guidelines for equine parasite control (published by American Association of Equine Practitioners) we do recommend a baseline of one to two annual dewormings that all adult horses should receive. The reason is that the fecal egg count mainly reflects the level of egg shedding with small strongyles, which are by far the most common and abundant parasites infecting horses. But other potentially important parasites such as tapeworms and large strongyles (bloodworms) are not readily reflected by egg counts

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