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April, 2008
Internal Parasites
Internal parasites can cause extensive internal damage without your ever realizing that your animals are heavily infected. Contrary to popular belief, horses can have high numbers of internal parasites while still appearing to be healthy. But parasites can take a heavy toll, particularly in young horses. Common signs of an infestation can include a dull, rough haircoat, decreased energy or depression, decreased stamina, loss of condition, slowed growth in young horses, pot belly (especially in young horses) colic, and diarrhea.
Horses can be infected by more than 150 species of internal parasites. The most common and troublesome are large strongyles (bloodworms or redworms), small strongyles, roundworms (ascarids), tapeworms, lungworms, pinworms, bots, and threadworms. Horses are most often infected by the first four; large and small strongyles, roundworms, and tapeworms.
The life-cycle of endoparasites differs from species to species, but generally goes like this; the eggs or larvae are deposited on the ground when the horse defecates. They are internalized when the horse is grazing or nibbling at the ground. The larvae mature into adults in the stomach or intestines. In some parasite species the larvae migrate out of intestines, into other tissues or organs before returning to the intestine, and maturing into egg-laying adults.
The use of dewormers is just one part of an effective
parasite control plan. Since parasites are primarily transferred through
manure, good management should include the following:
• Pick up and dispose of manure regularly (at least twice a week,
even in dirt or sand yards).
• Use a feeder for hay and grain rather than feeding on the ground.
• Compost the waste in an area distant from your pasture rather
than spreading it on fields that are to be grazed by horses..
• Keep the number of horses per acre to a minimum to prevent overgrazing
and to reduce the number of parasite eggs and larvae.
• Mow and harrow pastures periodically so as to break up manure
piles and expose parasite larvae to the elements. (Larvae can survive
freezing temperatures but cannot tolerate extreme heat or dryness.)
• Keep foals and weanlings separate from yearlings and older horses
so as to minimize the foals’ exposure to all parasites, particularly
roundworms.
• Remove bot eggs from your horses’ haircoat.
• Consult your veterinarian; together set up a deworming program
and monitor its effectiveness.
Internal Parasites