Internal parasites are a primary cause of colic in horses and can cause or contribute to many respiratory, digestive, and performance problems. Though parasites are a constant concern for horse owners, the severity of the problem can be reduced by following a regular preventive deworming program for horses formulated by your veterinarian.
Horses are affected by four common internal parasites - bots, strongyles, ascarids and pinworms. Large and small strongyles, ascarids and tapeworms present the greatest health risks.
Tapeworms
Mites living in a horse pasture may consume tapeworm eggs from the feces of infested horses. Grazing horses may then swallow the mites and become infested with tapeworms. Tapeworm infestation in horses may lead to varying degrees of colic. Therefore, it is important to include treatment for tapeworms in your deworming plan. Because many deworming agents do not kill tapeworms, a specific product may need to be added to your deworming program. Consult your veterinarian for the most effective treatment plan for your horse.
Strongyles
Veterinarians diagnose strongyle infection from microscopic observation of eggs in the feces. Blood tests are often used to assess the seriousness of an infestation. Frequent deworming is recommended to reduce the risk of serious problems from these parasites. An appropriate prevention program should be discussed with your veterinarian.
Ascarids
To adequately control ascarids, foals should be first treated at 8 weeks of age and then every 6 to 8 weeks until they become 2-year-olds, or as recommended by your veterinarian. Colic sometimes results when young foals are dewormed for the first time.
Pinworms
Though less dangerous than other internal parasites, pinworms are annoying to the horse because they cause severe anal itching. A characteristic of pinworm infestation is rubbing of the tail and the anal region causing broken tail hairs and bare patches around the tail.
Horses acquire the parasite by consuming contaminated water, grain, hay or grass. Young worms mature in the large intestine in 3 to 4 months, then crawl part way out of the anus to deposit their eggs on the adjacent surface. The eggs hatch outside of the horse's body and become infective in a few days, although they can survive unhatched for several months.
Pinworms can be treated successfully with the same drugs that are effective against strongyles and ascarids.
Tapeworms
Mites living in a horse pasture may consume tapeworm eggs from the feces of infested horses. Grazing horses may then swallow the mites and become infested with tapeworms. Tapeworm infestation in horses may lead to varying degrees of colic. Therefore, it is important to include treatment for tapeworms in your deworming plan. Because many deworming agents do not kill tapeworms, a specific product may need to be added to your deworming program. Consult your veterinarian for the most effective treatment plan for your horse.
A final note on parasite prevention
Environmental measures that break the life cycle of internal parasites are as important as administering dewormers. Follow good management practices to control the frequency and spread of internal parasites.
- Remove manure daily from stalls and weekly from pastures.
- Be sure pastures and paddocks are well-drained and not overpopulated.
- Compost manure rather than spreading it on fields where horses graze.
- Use a feeder for hay and grain and avoid ground feeding.
- Initiate effective fly control programs.
- Routinely examine horses for telltale signs of infestation.
- Establish a parasite prevention and monitoring program with your veterinarian.