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Deworming treatments are often a regular component of horse
health maintenance, but many horse owners may not understand the
best schedule for their horse. While deworming regimens vary by
region, there are some ground rules for owners to follow as they
work with their veterinarians on a proper deworming schedule.
Dr. Thomas Craig, professor at Texas A&M University College
of Veterinary Medicine & Biomedical Sciences (CVM), who
specializes in epidemiology and the control of internal parasites
in equines and grazing animals, offered some insight into
deworming. Craig explained that in a given population of horses,
about 20 percent will have 80 percent of the total internal
parasites of the herd.
Another basic guideline is that deworming should be based on the
age of the horse. There is a drastic difference in the deworming
needs of a foal (less than a year) and an adult horse.
"What's effective in adults may not be effective in foals,"
Craig suggested deworming foals for the first time at two months
of age. Parascaris equorum are of particular concern at this
"I recommend using fenbendazole, a broad spectrumbenzimidazole anthelmintic, such as
Safe-Guard, or a pyrantel dewormer such as Strongid for foals two
months old," Craig said.
As the foal matures, it is recommended that the same treatment
be used at four and six months of age. When the foal reaches a year
old, Craig suggested using an ivermectin or moxidectin treatment
When worming adult horses (older than one year), the approach
changes considerably. The most dangerous parasitic threat to horses
are small strongyles, which are present in most horses. Craig
recommended testing mature horses through fecal samples to
determine the number and types of parasitic eggs in the horse's
"After strongyles, the rest of parasitic control is really just
a numbers game," Craig said. "In older horses, you really only need
to deworm horses with high numbers of parasites. Adult horses with
less than a few hundred eggs per gram can be relatively left
Craig suggested treating all horses during the winter with
ivermectin to combat bot fly larvae "A good reminder, is to treat
your horse with ivermectin around Christmas time," Craig said.
"They often acquire bot larvae during the fall months, so winter is
really the best time to deworm with ivermectin.
Aside from bot fly larvae, other, less common parasites are
pinworms and tapeworms. Horses with pinworms are typically kept in
stalls. One of the most common signs of pinworm infected horses is
an itchy tail. Craig suggested treating an infected horse with a
fenbendazole dewormer once a month, for three months along with a
good shampoo of the horse's rear end.
"The pinworm eggs can only survive about 30 days, so I recommend
vacating the stall for a month until the eggs die on their own,"
Craig added. "There is no product to kill the eggs, but allowing
them to die on their own can be helpful in preventing
Tapeworms can cause mild colic in horses because they often
attach to the valve between the small and large intestine. Craig
recommended deworming in the fall (September, October, or November)
with a dewormer containing praziquantel or a double dose of
These recommendations are all suggested guidelines for parasite
management in horses. Craig recommended following these guidelines,
particularly in the Texas region. Altering deworming according to
your horse's age and parasite testing results are the two most
important guidelines and can help horse owners develop an effective
and sustainable parasite program, Craig said.
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