FLIC
KR/B
AALA
NDS
with varying exposure to
dewormers. Most experts
claim that the dewormer is
effective if the levels of the
targeted parasite are reduced
by 90 to 95 percent from the
fecal to when you complete
the follow-up. They recom-
mend selecting a different
class of anthelmintics for
the targeted species if the
reduction in the percentage
suggests resistance.
However, knowing your
selected dewormer failed
the FERCT isn’t enough
information to guide you in
selecting the next dewormer.
When faced with resistance,
it’s important to know which
class the failed dewormer
falls in, because resistant
parasites will be resistant to
every dewormer within that
same class. Thus, you’ll need
to select a dewormer from a different class that’s indicated for your specific ani-
mal and parasite. All anthelmintics fall into one of three main classes, each with a
main active ingredient (see “Determine Your Dewormer,” above).
When you’ve chosen your next anthelmintic, be sure to administer it as soon as
possible to ensure the last FEC is valid for the next FERCT. It may take more than
a couple of attempts to find which dewormer works in your situation. Once you
find one, though, you’ll know which medication to grab the next time it’s needed
for that specific parasite. Just be sure to always conduct the FERCT to catch any
resistance as early as possible.Selective Deworming
Unfortunately, the prevalence of parasite resistance is so high that livestock
owners must do more than just FECs and FERCTs. You must also be judicious in
selecting which animals to deworm. One reason to choose carefully is that you’ll
want some parasites that haven’t developed resistance to remain in your pastures
and livestock. The theory is that allowing nonresistant parasites to remain will
cause them to share their genetics with the resistant parasites, thus weakening their
overall resistance over time.
This selective deworming may be accomplished in a couple of ways (although
you’ll still need to use FECs to help make your selections). The first option is to
select individual animals with possible genetic resistance to parasites. Generally,
animals that are healthy, productive, have good body condition, and tend to maintain
a low parasite load without deworming are often going to be the ones to select to not
deworm. They’re also the animals you’ll want to breed in an attempt to bring those
resistant genetics into your breeding program. But don’t wait to think about de-
worming until an animal becomes skinny, develops a shaggy coat, or goes off feed.
Always conduct a FEC first, and then assess for possible resistance next. The pri-
mary goal is to keep your livestock healthy and productive, regardless of resistance.Determine Your
Dewormer
Below are some of the popular anthelmintics
on the market. Use this as a guide when deciding
on the proper treatment for your livestock.BENZIMIDAZOLE CLASS
■ Albendazole (Valbazen)
■ Fenbendazole (Panacur; Safe-Guard)
■ Oxibendazole (Anthelcide)
■ Oxfendazole (Synanthic)IMIDAZOTHIAZOLE/TETRAHYDROPYRIMIDINE CLASS
■ Levamisole (Tramisol; Prohibit)
■ Morantel tartrate (Rumatel)MACROCYCLIC LACTONE CLASS
■ Ivermectin (Ivomec)
■ Eprinomectin (Eprinex)
■ Doramectin (Dectomax)
■ Moxidectin (Cydectin)The most significant change
required is the frequent use of fecal
tests. Just as war commanders must
know who their enemy is before they
can attack, livestock owners must
know what parasite has invaded their
stock. Each species of animal has its
own prime parasite. For goats, it’s
the barber pole worm; for cattle, it’s
the roundworm. But just because
a species has a primary parasite
doesn’t mean that’s the one afflicting
your herd. Fecals will identify the
specific parasites present, allowing
you to better select a dewormer that
targets those species.
At a minimum, a Fecal Egg
Count (FEC) should be performed
at least once each season, and a
Fecal Egg Reduction Count Test
(FERCT) should be conducted 10
to 14 days after administering a
dewormer (see “Tips for Collecting
Fecal Samples,” Page 68). While
the first fecal identifies the culprit,
the follow-up fecal is an invaluable
tool to determine the effectiveness
of your chosen dewormer, because
what works on one farm, or even for
one animal, doesn’t work in every
situation. Parasite resistance varies
within a herd, since most animals
tend to originate from different farms