Signs of pinworms in horses

Updated July 19, 2017

A single pinworm can grow to 1 3/4 inches and, with the help of its children, siblings and buddies, can kill a 544kg. horse. Preventive measures keep these troublesome intestinal parasites under control. This includes providing fresh water and feed, daily cleaning of stalls and administering dewormers. A visual inspection of the horse and stall can determine if the horse has pinworms.

Tail Inching

Horses exhibit broken hair near the top of the tail caused by rubbing the rear on an object. This symptom specifically indicates the presence of pinworms. Horses will sometimes rub their rears just to scratch an physical itch. You should see this sign combined with other symptoms of worm infestation before panicking at the sight of broken tail hairs.

Worm Sighting

Pinworms lay their eggs on the outer rim of the horse's anal cavity. You can see the worms while they lay their eggs. Fully grown pinworms also end up in the horse's manure. Occasionally, you may see its eggs in the manure and, more often, egg sacs on the anus.

Weight Loss

Horses with worms lose weight quickly and even with an increase of feed. Weight loss is a sign of all types of parasitic worms in horses. Look for other signs to ensure that you treat with the right type of dewormer. Most, if not all, dewormers treat pinworms. According to EquiSearch, the following are effective against pinworms–piperazine, fenbendazole, mebendazole (Telmin) and ivermectin. The fine print on the dewormer package will have the necessary information.


A horse can experience colic for a number of reasons, but chronic colic might be a symptom of an infestation of pinworms–or worms, in general. If you take all the precautions for preventing colic, such as feeding at the same time with the same feed each day, take the time to look for other signs of worms.

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