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Tapeworms Are a Threat to Horse Health


There are four major types of parasites: strongyles, ascarids, bots and tapeworms. Large strongyles are known as bloodworms and affect all ages of horses, but young horses are the most susceptible. Ascarids (roundworms) are the largest equine parasite and have their biggest impact on weanlings and yearlings. Bots are the larvae of flies that attach to the inside of a horse’s stomach. Bots don’t discriminate between younger or older horses, and may occur in all horses. Tapeworms can affect horses as soon as they start to graze.

All horses—including foals, which are born parasite-free—are at risk of internal parasite infections. Foals are exposed to internal parasites in many ways, including contamination of feed , water; contamination of bedding or grooming implements; or through flies. To help control parasite infections, it is important to practice good sanitation, including appropriate manure disposal; provide clean water and feed; monitor and manage grazing areas; and use a dewormer on a regular basis.

Unbeknownst to many horse owners, tapeworms may be attacking their horse’s digestive system. Here they rob the horse of nutrients and can cause permanent damage to the horse’s delicate intestinal tract.

Tapeworms are more prevalent in horses than owners may realize. Results of a study has shown that tapeworm levels vary across different regions of the United States. Prevalence exceeded 95 percent in the upper Midwest. And, overall, the equine tapeworm infection level in the United States is at 54 percent.

The relationship between horses and tapeworms is cyclical. Oribatid mites are found by the thousands in pastures and are active for most of the year. As the horse grazes, it ingests mites that can be infected with tapeworm larvae. Once inside the horse, the tapeworm latches on to the wall of the intestine, matures and begins harming the horse’s digestive system. Mature tapeworms shed egg-filled body segments, which are passed through the horse in manure, and the process repeats.

“Signs of horses with a tapeworm infection are colic, lack of growth, or a dull hair coat and unthrifty appearance,” says Frank Hurtig, DVM, MBA, associate director equine medical affairs, Merial. “However, many horses may be infected with tapeworms and very few, if any, exhibit any clinical signs.”

All horses are affected by internal parasites. However, parasites do not affect all ages of horses in the same way. Some parasites are most common in young horses, while others strike older horses more often.

Egg shedding is sporadic, so detecting tapeworms in horses is difficult. Standard test, such as fecal floatation, only rarely reveal their presence.

The best treatment for tapeworms in horses is the use of dewormer. “Horses should be dewormed every eight weeks and treated for tapeworms at least twice a year, especially in the spring and fall,” Hurtig explains.

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