Q: My horse is constantly rubbing his tail on anything he can find. It has become so bad that the hair at the base of his tail has either fallen out or become matted. Thankfully, I've finished my show season, but what is causing him to do this? He also seems to be losing weight. Are these two problems related?

A: Tail rubbing, commonly known as rat tail, broken hair, or matted tail, most often can be a symptom of pin worm infestation. Tail rubbing is a condition resulting from the horse's rubbing back and forth on an object--such as a fence post, feed buckets, or water buckets--in order to relieve the itching, or pruritis, which might be caused by the eggs of pinworms that are laid around a horse's anal area. The horse literally can take the hair off its tail by the amount of rubbing it does.

The guilty culprit in some cases of tail rubbing is the pinworm (Oxyuris equi); this is not always the case. Other reasons horses rub the hair off their tails include the following: insect hypersensitivity, food allergy, pediculosis (lice infestation), mange, or in rare cases a behavioral vice much like cribbing.


Pinworms usually are the cause of the irritation that leads to tail rubbing. Note the broken hair at the base of the tail.

For this article, we will concentrate on pinworms as the cause. According to E. T. Lyons, PhD, of the Gluck Equine Research Center in Lexington, Ky., the worm itself is not really the cause of the itching; the cause is the microscopic eggs the females lay at the horse's tail area around the anus. It is believed that most of what causes the horse discomfort is the result of the gelatinous agent that surrounds the eggs of the pinworms. Also, the pinworms, because of their fragile nature, might rupture when they are around the anal region and contribute to the irritation.

Normally, you will not see the pinworms themselves if you examine your horse's anus area because the female worms come out of the anus at night to lay eggs. To test for pinworms, your veterinarian will use clear tape and adhere it to the perianal area to take a sample to determine if pinworm eggs are present. The samples the tape picks up will be observed under a microscope by your veterinarian to determine if pinworms are the source of irritation.

Any age horse can be infected with pinworms. However, mature pinworms usually are found only in younger animals. Immature forms can be present in all ages of horses, but tail rubbing caused by pinworms only involves adult pinworms. The reason for this is that the life cycle of a pinworm is five months, so the worms themselves have not matured until the horse is at least five months of age.

Tail rubbing occurs in all regions and climates of the United States, although the problem is seen most often in warm and humid areas. This probably is true because warm, humid climates have more insects, and the tail rubbing could be a hypersensitivity to insects.

Treatment for tail rubbing due to pinworms is simple--institute a regular deworming program. A regular deworming program will nearly always rid your horse of the parasites that cause tail rubbing. Dewormers such as ivermectin, benzimidazoles, moxidectin, or pyrantel pamoate are available and will eradicate these parasites.

If an active deworming program is already in place, then you will need to look at alternate causes of your horse's tail rubbing. Sometimes after the horse already has been wormed and eradication of the pinworms was successful, your veterinarian will need to treat the horse with antibiotics and antifungals to aid in the healing process of the tail. Some horses might even have bits and pieces of debris from fences, or other objects they have rubbed against, embedded in their tail. Have your veterinarian check and remove this material.

Treatment in the form of deworming is very effective at stopping tail rubbing caused by adult pinworm infection. Keep in mind that after your horse stops rubbing its tail, it will take a month or two for the hair to grow back. There usually are no long-term complications associated with tail rubbing. Once the pinworms have been eradicated, the horse should recover to his normal condition.

My recommendation to prevent this problem from occurring is to initiate a continuous deworming program that incorporates good management practices. Pinworms are transmitted from fecal material by oral ingestion. Many times if one horse is affected by pinworms, the whole herd will become infected unless the horses are involved in a deworming program. This happens since the horse often is rubbing its tail on community feed buckets and water troughs and in the process depositing pinworm eggs, which hatch into larvae and are ingested by other horses. Horses fed off the ground are more at risk of ingesting the pinworm larvae because the larvae can fall off the infected horse to the ground. If your horse is rubbing its tail, have your veterinarian check the horse as soon as possible.

Also keep in mind that horses infected with pinworms might experience complications other than tail rubbing. There is no definite proof of digestive disturbances being caused by pinworm infection, although larvae might denude the mucosa of the colon. Possibly, there might be some digestive-related problems due to "stress" from tail rubbing.

About the Author

Robert E. Holland Jr., DVM, PhD

Robert E. Holland Jr., DVM, PhD, is a senior technical service veterinarian for Pfizer Animal Health. He served on the AAEP task force revising equine vaccination guidelines, and his research interests include virology, biomechanics, drug testing, and air flow.

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