By Jennifer Ross, DVM Gastrointestinal parasitism is a common health problem in horses. Parasites can produce a varying degree of damage depending on the type and number of parasites present and the immune status of the horse. Problems associated with parasitic infections include diarrhea, weight loss, colic, poor growth and unthriftiness. Virtually all horses are infected with parasites.
Horses are susceptible to a variety of gastrointestinal parasites.
The most common equine parasites are large and small strongyles, ascarids, bot fly larvae, and pinworms. With the exception of bot flies, horses become infected by ingesting infective eggs or larvae while grazing on contaminated fields or by licking contaminated objects. After migrating through the intestinal wall, the larvae invade various organs before returning to the small or large intestines where they reach maturity and produce eggs which pass out with the manure. Larvae then travel to the mouth and migrate to the stomach where they attach to the stomach wall. The main goal of parasite control is to optimize the health and performance of horses.