Clinic Hours:
Mon-Fri 8 to 5:30
Sat. by appointment only

31310 Woodhaven Trail
Cannon Falls, MN 55009

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Phone Numbers:
651-258-4050 office
651-258-4051 fax
651-222-0885 Twin Cities


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Equine Intestinal Parasites
(In order of clinical significance)
Small Stronglyes (Threadworms)
Currently the most common parasite of the adult horse! It is easily picked up while grazing. They can live encysted within your horse for up to 3 years and when they emerge they can cause dramatic symptoms such as weakness, colic, diarrhea, weight loss, and death. The eggs can survive freezing temperatures but die at about 85 degrees (in compost).
Large Stronglyes (Bloodworms)
The life cycle begins where the female lays eggs in the intestine and are passed in the feces. Under cold and dry conditions, the eggs can survive unhatched for long periods to emerge when conditions are warm and moist. The hatched larvae are ingested by grazing horses. After a period of migration (up to 300 days) the young adults arrive back into the intestine. A female strongyle can lay up to 500 eggs per day. They are also called bloodworms because the immature worms migrate through the blood vessels of the intestine sucking blood and causing arterial damage. Sudden death can occur from an aneurism caused by larval damage.
Ascarids (Large Roundworms)
They mostly affect young horses by large numbers accumulating in the small intestine interfering with the horses nutritional absorption. Foals acquire infective eggs from feces passed by other horses, contaminated hay, or water. The eggs hatch in the intestinal tract and the young worms burrow into the intestinal wall. It takes about a week for them to travel to the lungs, where they are coughed up and swallowed a second time. They mature in the intestine in 2-3 months and eggs are passed in the feces starting anew. Females can lay up to 200,000 eggs per day.
They are the larvae of the Bot fly. Since they are common in the horses environment, it is almost impossible for a horse not to be infected. In late summer and fall the bot fly lays its eggs on the hair of the chest, forelegs, throat, and nose. Stimulated by the horses licking ,the eggs hatch and migrate into the horses mouth and settle in the gums, cheek, and tongue. After a month the larvae then move to the stomach and attach to the stomach wall interfering with digestion and blocking the opening to the small intestine. They are then passed in the feces 8 to 10 months later and mature to adult bot flies to start the cycle over. Bots can also invade humans mouth tissue and cause irritation but can not develop so they die in a few days.
Eggs are found in contaminated feed, water or bedding. After ingestion, the worms mature in the colon and crawl part way out the anus to deposit their eggs on the anus. This causes severe irritation and the horse will often rub its tail and anal region excessively resulting in broken tail hair and bare spots.
Three types of tape worms can be found in horses. Horses become infected when they accidentally ingest mites that are infected with immature forms of the tapeworm. It takes 2 months for the tapeworm to mature. It is hard to detect if a horse is truly infected without seeing a full worm passed in feces. For this reason Dr. Winter highly recommends targeting tapeworms at least once a year preferably in the fall.
Other Parasites
Other parasites, such as stomach worms, whipworms, and lung worms can cause problems but are more rare. Lungworms are most commonly found in donkeys.

Click here to print/view the Paste De-wormer Chart.



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