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Combatting Intestinal Parasites
The Enemy
Smart horse owners know the best offense against equine parasites is a strong defense based on identifying
and understanding the enemies that threaten your horse’s health.* Check out the six worst offenders below.
Roundworms
Threat: High to Severe
LIFECYCLE:
Mature eggs are ingested
when eaten through the feces and
environment; larvae migrate through
intestinal wall to the liver; blood carries
larvae from the liver to lungs; larvae enter
airways and are coughed up into mouth;
larvae are swallowed and become adults in
the small intestine; adults lay up to 200,000
eggs per day; eggs are expelled in feces.
Approximate 80-day cycle.
SYMPTOMS:
Signs of respiratory
disease including nasal discharge and
cough. Signs of intestinal disease including
weight loss, pot belly, poor condition,
digestive problems, impaction colic, bowel
rupture, and death in some cases.
Encysted Small Strongyles
Threat: Moderate to Severe
LIFECYCLE:
Eggs in feces; 1st & 2nd
stage larvae in soil or feces; 3rd stage larvae
ingested by horses from mangers, grass, feed,
etc.; larvae burrow (encyst) into intestinal
walls for months or even years; when large
numbers of cyathostomes emerge from
“hibernation”within the intestinal wall and
re-enter the intestines, severe disease can
occur; adults live in large intestine and
produce millions of eggs expelled in feces.
SYMPTOMS:
During the encysted stage,
the horse may have poor feed conversion
and lethargy. Upon sudden emergence from
encysted stage, loss of appetite, diarrhea,
anemia, lethargy, colic, and even death in
extreme cases can occur.
Large Strongyles
Threat: Moderate to Severe
LIFECYCLE:
Eggs in feces; 1st & 2nd
stage larvae in soil or feces; 3rd stage
larvae ingested by horses from mangers,
grass, feed, etc.; larvae migrate from large
intestine through blood vessel walls
or other organs; adults live in the large
intestine and produce millions of eggs
expelled in feces.
SYMPTOMS:
Weight loss, digestive
problems due to obstructed blood flow to
portions of the large intestine, dull coat,
poor appetite, lethargy, pot belly, liver
problems, colic, and even death in extreme
cases.
Pinworms
Threat: Moderate
LIFECYCLE:
Eggs are laid around the
anus of an infected horse; eggs fall to the
ground and are ingested by other horses;
eggs hatch in the stomach (occasionally
other organs) and remain there until
larvae are mature; larvae migrate to the
large intestine and colon; adults migrate
to the anus and lay eggs there before
withdrawing back inside.
SYMPTOMS:
The adhesive nature of
the deposited eggs is irritating and causes
horses to rub their tail and rectal area to
relieve the itching resulting in damage to
hair and skin.
Tapeworms
Threat: Moderate
LIFECYCLE:
Horse ingests a mite
infected with larval tapeworm; larvae
develop into adult tapeworms in the
intestine in about two months; adult
tapeworms live in intestine and absorb food
as it passes by; adults produce eggs that are
passed in horse feces; mites eat eggs; eggs
produce larval tapeworms inside the mites
in two to four months.
SYMPTOMS:
Poor growth in young
horses, poor condition overall, inflamed
intestines, intermittent diarrhea, and/or
colic.
Bots
Threat: Low
LIFECYCLE:
Bot flies (three species)
lay yellow or gray eggs on horse’s hair on
legs, mane, flanks, jaws, throat or lips in late
summer; eggs enter the mouth when licked
by horse; eggs hatch into larvae, remaining in
the mouth up to three weeks; larvae migrate
to stomach and small intestine and attach
to the lining for about seven months; larvae
pass out in feces and enter the soil; over two
months, larvae develop into adult flies; adult
flies lay eggs on hair on horse’s legs and trunk.
SYMPTOMS:
Digestive problems, dull
coat, and colic.
*A fecal exam is the most reliable way to be sure you’re treating your horse for the right
parasites. Check with your veterinarian before starting any deworming program.
AFFECTS:
Foals and young horses
under age two are most vulnerable, as
an infestation can severely affect both
respiratory and digestive systems. Adult
horses develop some immunity unless
infestation is extreme and unchecked.
AFFECTS:
All ages are vulnerable, but
young horses and immunocompromised
adults are most susceptible. Upon
emergence, severe inflammation and
bleeding in the intestine causes normal gut
action to be affected, resulting in diarrhea,
anemia, colic, and occasionally death.
AFFECTS:
Especially dangerous to
young horses under age two, and all horses
if infestation is left unchecked. Migrating
larvae damage blood vessels, intestinal
walls, and organs such as the liver.
AFFECTS:
Can affect all ages. Although
relatively harmless to a horse’s overall
health, itching from pinworms can cause
damage to hair and skin.
AFFECTS:
All ages are affected, as
immunity isn’t apparent. Young horses
under age two may be more susceptible
to problems. Heavy infestation may affect
various areas of the intestinal tract, causing
scarring or severe inflammation.
AFFECTS:
All ages can be affected. Bot
larvae damage the lining of the stomach
and small intestine, interfere with the
passage of food, and may cause other
digestive problems.
