Page 19 - Parker Co. 4-H Connection September 2021

4 - H H O R S E P R O J E C T

Small Strongyles
These worms are much more common. The symptoms can be similar to that of large strongyles, but the way
these worms cause symptoms and where they live within the gastrointestinal system is different. The larvae,
or immature stage of small strongyles, encyst in the lining of your horse’s small intestine over winter after
your horse has grazed contaminated pasture. The following spring, these encysted larvae, come out of their
winter homes within your horse’s gut lining in a mass exodus. This can cause significant damage to the
intestines.

Ascarids

Ascarids live in the small intestine of the gut. They are common in foals and can be particularly dangerous.
Worms are acquired from grazing. The worms can penetrate through the gut wall and migrate to the liver
and/or lungs. They are then coughed up and swallowed, where they then develop into adults within the
gastrointestinal system. Because these worms can migrate to the lungs, infected horses may show signs of
respiratory disease such as cough or nasal discharge.

Bot Flies
During the summer months, bot flies lay small yellow eggs on your horse’s legs and coat. Horses ingest these
eggs when they itch or groom each other. The eggs molt to the larval stage within your horse’s mouth and then
migrate to the stomach, where they attach to the gut lining. They do not usually cause serious health problems
but can lead to ulcers within the stomach.

Pinworms
The most common clinical sign of pinworms is a horse that is continuously rubbing its bum. The worms live
in your horse’s rectum and exit only to lay their eggs around the perineum. This is particularly itchy, so horses
may be seen to itch their hind end on water buckets, feeders, and other objects. Pinworms are a problem for
horses housed indoors because they will itch where they eat, and therefore ingest the worms again,
continuing the worm’s life cycle. To diagnose pinworms, your veterinarian will use the scotch tape test and
look for the eggs under a microscope.

Habronema

Habronema are stomach worms that can cause inflammation of the stomach as well as sores on the skin.
These worms have an interesting life cycle and require an intermediate host, or middleman. Horses are
infected by ingesting flies that are carrying the larval stage of the worm. These flies can also lay the eggs on
your horse’s coat and cause the characteristic “summer sores” that present as yellow or white crust-covered
wounds that normally have a blood-tinged draining fluid.

Tapeworms

There are several species of tapeworm, and each species colonizes a different part of your horse’s gut. The
most common tapeworm, Anplocephala perfoliata, often causes impactions at the ileocecal junction. This will
cause your horse to show signs of colic. Horses may also show signs of unthriftiness and anemia.
Gastrointestinal ulceration can occur where the tapeworms attach to the inner lining of your horse’s gut. Eggs
are shed in feces sporadically, so they are often difficult to detect from fecal samples. Tapeworms also require
an intermediate host, the mite. Once the eggs are passed in your horse’s feces, the mites ingest the eggs, and
then your horse will inadvertently ingest the mite when grazing pasture or eating hay.

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