Equine pinworms are parasites that live in the large intestines of horses. At night the females lay eggs on the skin around the rectum. These eggs can fall off the host and contaminate pastures where they are ingested by other horses. While not particularly harmful, pinworms do cause irritation. The glue on the eggs causes the horse to rub its tail and may lead to hair loss and sores. Pinworms can usually be controlled by dewormers along with sanitation of the stable.
There are three main classes of dewormers. Benzimidazoles contain active ingredients such as fenbendazole, oxfendazole, oxibendazole or febantel. They are extremely safe and effective for treating pinworms when administered properly. However, they have been known to lead to parasite resistance. Tetrahydropyrimidines containing pyrantel salts are another effective chemical dewormer. A third class of dewormer, avermectins, contain the active ingredient ivermectin. They are up to 100 per cent effective against pinworms as well as other internal parasites.
When your vet has diagnosed pinworms, discuss the treatment options and schedules. One schedule may involve treatment with a dewormer four to six times a year. Since temperatures above 29 degrees C (85F) kill most larvae, it is not necessary to provide treatment during the hot summer months. A second schedule calls for daily deworming with a low-dose feed. In addition to the feed, use another class of dewormer one or two times throughout the year. A final protocol calls for targeting the horses that are infecting the herd. After a fecal egg count test determines which animals are infected, treat those horses with the recommended chemical dewormer. Alternate the class of dewormer you use to prevent parasite resistance. Treat foals every 30 to 60 days in their first year.
An important aspect of pinworm treatment is maintaining sanitary conditions. Prevent overcrowding of pastures so parasite infested manure doesn't build up. Remove manure daily and compost it or spread it in ungrazed areas. Rotate pastures if possible. Drag pastures during hot summer months when the sunlight can kill the larvae. Avoid ground feeding by using bunks or mangers, and make sure the water supply is clean. Since pinworm eggs are lightweight, they can become airborne and contaminate a stable. When treating a pinworm infestation, be sure to carefully clean the stable and surrounding areas.