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Worms in horses

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Worms can be harmful to the horse and make feeding and
walking in the pasture a very miserable and a difficult
experience. If a horse has too many worms in its body, it
could die. De-worming a horse once a year is recommended to
ensure that worms will not survive to multiply and take
over the horses body. Ask a veterinarian which medications
the best for preventive de-worming. There are many on the
market today that can kill one or more species of worm.
Horses contract worms from poor living conditions, other
horses that have been mistreated, and from contaminated
drinking water. Cleaning out stalls and refreshing water
everyday is one way to prevent spreading the worms to the
other horses living in the stable. 


Left: De-worming a horse. Right: Ascarids

Types of

There four types of
worms that can affect a horse. These include strongyles, tapeworms, ascarids, and
. The first three can infect a horse through the
feces of other horses. If a contaminated horse leaves feces
on the ground and another horse steps on it and moves it
around the rest of the stable, it will eventually get into
the feed, grass, and into the water.

• Strongyles, which
seem to affect younger horses the most, begin as larvae
growing up in the arteries, gut wall, and liver. As they
grow, they travel through the body heading for the large
intestine where they will live out their lifespan. Once
inside the large intestine, strongyles will feed of the
digested food leaving little nutrients for the horse. This
can cause several problems. Stunted growth, intestinal
problems, artery collapse, and eventually death are common
in horses affected by strongyles. By separating the older
horses from the younger horses, this parasite has less
chance to infect the horses. 

• Tapeworms are usually
uncommon in horses. They, too, are transferred by unclean
stall conditions and through feces. Tapeworms can live for
years inside the stomach lining of its host. But if many
tapeworms gather in the stomach, this can cause blockage,
which could cause the horse to die. Tapeworms can be up to
twelve inches long. They too keep a horse from receiving
proper nutrients from food. There are many things horse
breeders can do to prevent the spread of tapeworms.
Rotating feed to make sure it is free of feces and clean
out stalls often will prevent the spread of this parasite.
Since the tapeworm is the least common of all parasites, if
stalls are cleaned, infestation should not be a problem.
Keep in kind that getting rid of a tapeworm is far more
difficult to deal with than contracting one. Tapeworms can
grow back if the head of the worm is not removed with the
rest of its body. Killing one with medicine takes time. The
damage could already be done, so proper prevention is

• Ascarids are worms
that affect the liver and the small intestine. These worms
are similar to strongyles in that they affect younger
horses. As with the other worms, proper cleaning of stalls
is important in keeping infestation to a minimum. If not
treated, the horse will probably die from colic or an

• Bots are transferred
differently from the other worms. These worms transport by
insects that land on the horses hair, such as flies. The
horse ingests the eggs, which turn into larvae on the
horses tongue. Eventually, the worms make their way to the
stomach where they live on digested food and stomach acids.
This can result in a smaller, weaker horse that has not had
the proper nutrients to survive. Bot eggs should be removed
by cutting eggs out of the hair on the horse or by wiping
them off with warm water. This will prevent the horse from
digesting them. 

Horses must be kept in clean stalls that are refreshed
every few days with new grass and hay. Drinking water
should be changed at least once a day. Grooming horse often
will prevent bots and other worms from getting into the
horse. Young horses need to be separated from the older
ones during pasture times if at all possible. This will
prevent the spread of strongyles and ascarids. Keeping all
horses that live in the same stable together and not
letting them graze with horses from another stable is a
good idea. Since worms are easy to spread, proper
precautions will make it harder to contaminate a horse.

There are many types and brands of the paste
dewormers on the market now. An essential thing to remember
about these paste dewormers is that no matter what the
makers may say on the box, you should always rotate types
of chemicals used (according to your vet’s instruction). If
you fail to rotate, the parasites can develop an immunity
to the type of chemical being used and begin to prosper
inside your horse again despite the dewormer being