Life Cycle of Worms
1. General Signs of Worms
a. Excellent appetite, but unable to gain weight
b. Rough, dull hair coat
c. Thin, unthrifty appearance
d. Rapid tiring during hard work
e. Tucked up flanks
f. Digestive disturbances, such as diarrhea, constipation or colic
g. Anemia
h. Acute, heavy infestation may result in fever, depression and lack of appetite
2. Ascarids (roundworms)
a. Appearance
i. Yellowish/white in color
ii. 9-12 in in length
iii. Commonly found in foals and young horses
b. Life course
i. Adult female worm deposits eggs in small insects
ii. Eggs passed on in feces and live in soil for long periods
iii. Horse eats contaminated dirt, food, water or manure
iv. Eggs pass to small intestines where they latch to larvae
v. Larvae penetrate the intestine wall and enter bloodstream
vi. Larvae travel to blood to the liver and lungs
vii. Large are coughed up from lungs
viii. Larvae are swallowed again
ix. Larvae reach small intestine where they develop into manure adult
roundworms.
c. Damage
i. To lungs and liver
ii. Severe blockage of intestines and get colic
iii. Lunge damage can result to pneumonia
3. Strongyles (bloodworms)
a. Appearance
i. Can get up to 2 inches
ii. Horses of all ages get this
iii. These are the most important and serious parasite
b. Life course
i. Worm eggs are passed out of feces
ii. Eggs develop into larvae on the ground
iii. Larvae crawl onto vegetation
iv. Horse ingests larvae while grazing
v. Larvae penetrate the wall of small intestine and enter bloodstream
vi. Larvae travel through bloodstream to cecum and colon
vii. Larvae penetrate wall of cecum and colon and develop into adults.
c. Damage
i. To lunge, heart, liver and intestines wall
ii. Permanent damage to blood vessels causing blood clots
4. Pinworms (rectal worms)
a. Appearance
i. Female measure up to 6 inches, males measure up to 1 inch
ii. White color and thread like
b. Life course
i. Female pinworms are passed out feces and deposit eggs in feces or
around anal area
ii. Horse ingests eggs by eating contaminate feed, water, manure or dirt
iii. Adults live in dorsal colon. Mature female worms crawl out of rectum and
deposit more eggs on surrounding skin. These eggs are rubbed off or
passed out in feces and infest other horses.
c. Damage
i. Mild inflammation of the lower intestinal tract
ii. Presence of eggs around anus causing itching
5. Large Stomach Worms
a. Appearance
i. White in color and slender in appearance
ii. Measure ½ to 1 ¼ inch in length
b. Life Course
i. Adults in stomach. Females lay eggs in stomach
ii. Eggs are passed out with feces
iii. Flies lay eggs in feces
iv. Worm eggs are eaten by fly maggots; young worms develop in the fly
maggots and pupa
v. Adult flies carrying infective larvae emerge
vi. Horse ingest infective flies or larvae when flies feed on horse’s saliva
vii. Larvae are ingested by horse and travel to stomach to mature and lay
eggs again.
c. Damage
i. Inflammation of the stomach wall
ii. Summer sores in eyes or moist wounds
6. Bots
a. Appearance
i. Not worms. Larvae of the bot fly
ii. Bot flies are yellowish, hairy and bee-like flies
iii. Bot eggs are white, yellow or black
1. Found on forelegs, around moth of under jaw
2. Size of pin head.
b. Life Cycle
i. Mature fly lay eggs on horse’s body
ii. Horse licks or scratches eggs with tongue or teeth
iii. Moisture from Tongue induces the eggs to hatch. Larvae invade the
mucous membrane of horse’s mouth
iv. Larvae migrate to stomach where they attach to stomach wall and
mature.
v. Mature bots are passed out in feces.
vi. Larvae pupate in the ground
vii. Adult flies emerge
c. Damage
i. Inflammation of stomach wall
ii. Heavy infestation can cause rupture of stomach
7. Prevention
a. Worm horses every 3 months or on schedule set by vet
b. Take regular fecal samples to vet to to check for eggs.
c. Foals wormed 6 seeks of age.
d. Worm mare 30 days before foaling
e. Proper sanitation measures
i. Place horses on clean pastures
ii. Dispose of manure properly
iii. Keep stalls clean and paddocks clean
f. Avoid putting a large number of horse on a single pasture
g. Pasture rotation.
h. Wash rectal or dock are to remove eggs. Don’t use clothes or brushes on any
other areas of horse
i. Take bot flies off by clipping, shaving or saturating them with vinegar or take off
with bot knife.
j. Eradicate flies in barn