then again 14 days after deworming,
and the two numbers are compared.”
“To know which products work,
there’s no other way to determine
this but to use fecal testing on high
shedders and working with your vet,”
says Cheramie. “When you look at
FECRT, you hope to see 90 to 95
percent or better reduction; anything
less than that raises concerns about
“Testing the efficacy of dewormers
after use (through FECRT) defines
the best drug for your horse,” says
Kennedy. “If the dewormer you used
is working and you used it correctly,
you can keep using it.”
Efficacy testing should always be
done on a group of horses; it is not an
individual horse diagnosis.
FOR BEST PROTECTION,
ALL HORSES ON THE SAME
PREMISES SHOULD BE
DEWORMED THE SAME
WAY AT THE SAME TIME.
The most effective parasite control program is based on a specific
population of horses that share an
environment. The drug class used also
depends on the timing and the class
of horse being treated.
dewormed more often during the grazing season in your area.” Talk to your vet for
advice about which dewormers to use, how often and when.
“Checking for the presence of worm eggs is a valuable check-up for your chosen
approach to parasite control,” says Kennedy. “[But] testing must be conducted and
MY HORSE’S FECAL ALWAYS COMES BACK NEGATIVE,
SO THAT MEANS I DON’T NEED TO DEWORM HIM.
“A negative fecal egg count test does not mean a horse is para-
site-free,” says Gray. A horse with a negative fecal may still have
intestinal parasites; those parasites simply are not actively shedding eggs.
However, parasitologists emphasize that egg counts do give valuable information. Even when results are negative, these horses still need to be dewormed but
will only require a minimum of recommended treatments.
“It’s important to keep in mind that even though a fecal egg count may not
always directly correlate with the magnitude of an intestinal worm burden, it
is still the best tool to determine parasite risk and to help direct our course of
treatment,” says Morgan.
ROTATING DEWORMERS EVERY TWO MONTHS
IS THE BEST WAY TO PROTECT AGAINST PARASITES.
Several decades ago, horse owners were advised to rotate between
the three chemical classes of dewormers: benzimidazoles (such as
fenbendazole and oxibendazole), pyrantel, and macrocyclic lactones (ivermec-
tin and moxidectin). Over the years, parasites have become widely resistant
to benzimidazoles, somewhat resistant to pyrantel, and are showing emerging
resistance to macrocyclic lactones.
“We’ve learned that rotating between chemical classes didn’t slow parasite resist-
ance like we thought it would,” says Gray. “It’s important to make sure the dewormer
you’re giving is still effective in your horse and on your farm. Your veterinarian can
help with that by performing a fecal egg count reduction test (FECRT),” she contin-
ues. “Instead of counting eggs just once, a fecal egg count is done before deworming, M E L O R Y
No. 5 Myth