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Sat. by appointment only
31310 Woodhaven Trail
Cannon Falls, MN 55009
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651-222-0885 Twin Cities
Equine Intestinal Parasites
(In order of clinical significance)
||Small Stronglyes (Threadworms)
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)
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 horse’s 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 horse’s 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 horse’s 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 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, 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