Lana,
Found out recently that internal parasites have become resistant to Ivomec. Lost some "good ole'" cows before we got it figured out.
Any input on this subject?
Thanks,
Lee
I just started reading an article about this in the Nebraska Farmer yesterday. Heres the start of the article.
THE glowing orb of nearly magical
cattle dewormers may be setting
in the west.
A growing body of worldwide
research is showing
cracks of resistance in the
armor of these mighty drugs,
with sheep, goats and horses
leading the downfall and cattle
teetering on the edge.
The buzz these days in the
cattle industry is about how
important parasites, especially
some of the roundworms, may have
become resistant to the anthelmintics.
This refers to such amazing dewormers
as the ivermectins, the benzimidazoles
and the imidazoles.
Said brusquely, all the major dewormers
— the most-used, mostcommon
and most-effective dewormers
on the market — are creeping toward
failure.
Naturally, there is much snarling and
gnashing of teeth among the industry
giants and some among scientists, but
the evidence suggests beef producers
Even the best dewormers
could lose their potency
need to become more insightful and vigilant
about how they use and monitor
these potent potions.
“You’ve got two groups of people
out there: those who say
anthelmintic resistance is
rampant and those who
say it doesn’t exist at all,”
says Louis Gasbarre, a wellknown
researcher in this
fi eld and the research leader
of the Bovine Functional
Genomics Laboratory, a USDA
Agricultural Research Service
facility at Beltsville, Md. “And
it depends on who’s selling what drug.
“The problem is that everybody
who’s out there telling the producers
what to do has a horse in the race,”
Gasbarre says.
Indeed, if you listen to the anthelmintic
manufacturers long enough, and
read between the lines of their banter
about what’s more effective and which
tests and studies are valid and which
aren’t, you could get the idea they’re
fi ghting over market share.
Meanwhile, there now have been
documented cases of resistance and/or
Why the fecal egg count reduction test?
SOME people have cast dispersions on the fecal egg count reduction test, implying
it is not an appropriate method of determining anthelmintic effi cacy.
However, it is the currently accepted method, the standard, and probably the
best method available at this time, says Bert Stromberg, parasitologist at the
University of Minnesota.
It is the method chosen by consensus of nine parasitologists on the
Anthelmintic Resistance Roundtable, which was sponsored by the company
Intervet and fi rst met during the 2005 American Association of Veterinary
Parasitologists annual convention. Stromberg says this group is well distributed
across the U.S. and also has reasonable variation in experience and opinion.
“I think it is not the ideal test. But it is the best thing that we have,” Stromberg
says.
This test has some strengths. Regardless of herd size, a sample of 20 animals
is considered statistically adequate.
It is standardized, and it has been consistent. Stromberg says the three labs
involved in the National Animal Health Monitoring System survey have all run
samples on an 80-head herd and found they are only decimal points apart on
percent reduction — which is the key measure.
lowered effi cacy in the U.S., not to mention
England, Brazil, Argentina and New
Zealand. The current pattern in this
country seems to be problem areas or
operations where resistance to anthelmintics
is becoming more common.
“The real question that has yet to be
answered is how extensive is it and what
exactly is going on,” Gasbarre adds.
He hopes the new National Animal
Health Monitoring System report that
will be released sometime this year will
provide more insight. He adds that yetunpublished
work just being completed
is confi rming this trend toward anthelmintic
resistance, while other reports
in the U.S. show anthelmintics are still
working well.
“What we’re telling producers right
now is — as with any antimicrobial, and
that’s essentially what anthelmintics are
— repeated use of the drug is going to
select for resistance,” Gasbarre says.
“I think the real point is we’ve selected
parasite populations by selection
over about 40 years of use of macrocyclic
lactones. They’ve been wonderful
drugs. We may never see anything quite
that good again,” he notes.
On the farm or ranch, beef producers
need to be monitoring the effects
of their deworming programs, he
suggests. If they apply the right products
in the right manner and the normal
results don’t appear, it may be time to
check product effi cacy with fecal samples
before and after treatment.
Gasbarre says in a yet-unpublished
study of a West Virginia bull test, he saw
this sporadic pattern continuing.
New day dawning
Further, the villains in this drama may
be changing.
The brown stomach worm Ostertagia
ostertagi has long been looked upon as
the most economically damaging worm
in cattle. There is good reason for this,
Gasbarre explains. It is very pathogenic,
or very able to cause disease; it has the
ability to evade the immune response
of cattle; and it tends to persist in the
animals’ systems.
However, two other nematodes
may be becoming newer and more
powerful animals, so to speak. It’s possible
new, pure strains of Cooperia and
Haemonchus could yet show themselves
to be quite problematic for cattle,
Gasbarre suggests.
“We don’t know how pathogenic
these pure cultures are,” Gasbarre says.
“We know they can exist in extremely
high levels. We also know that in one
case it is well documented — we actually
documented this working with
Larry Smith up in Wisconsin — that
the producer actually had animals die.
That turned out to be an almost pure
Cooperia infection. I would say that’s
pretty indicative the parasite is pathogenic
or can be pathogenic.”
Further, he adds that knowledge
about the Cooperia parasite has been
done with a strain known as Cooperia oncophora,
which prevails in the northern
and central U.S. and in Europe. The
small amount of study of pure strains
of Cooperia has been on this critter. Yet
there appears to be a southern strain
of the Cooperia nematode that is more
highly pathogenic, he warns.
“I think to say, ‘This is not going to
pose an economic problem because it’s
a nonpathogenic species’ is a real understatement
of the problem,” Gasbarre
says. “I think if you were a prudent individual
you would say, ‘We don’t know
enough about these forms to adequately
say that they’re going to be nonpathogenic.’
I think we have enough evidence
that shows that they can be, and the
producer needs to be concerned about
them.”
“When you use ivermectin, you
have Cooperia and Haemonchus both
persisting post-treatment,” says Tom
FREQUENCY MATTERS: Cattle
operations that use dewormers the most
could be most at risk.
RSC
