Clearwater County Highlights October/November | Page 24

24 | NOV. 2016

Livestock Producers Concerned Over Growing Parasite Resistance
Some Suggested Management Practices
to Help Maintain Effectiveness

Producers are
encouraged to
consult their
veterinarian
to develop
a long term
parasite control
strategy.

www.clearwatercounty.ca

The evolution of parasite resistance is an
increasing concern for livestock producers
and the cattle industry in particular.
Controlling parasites in livestock has been
a challenge since man first domesticated animals. By the end of the nineteenth century a
demand developed for control methods that
would reduce disease and livestock losses.
Over time different methods such as arsenical solutions and organic acaricides were
developed to treat external parasites, each
losing effectiveness over time.
More recently introduced were the macrocytic lactone family of chemicals, which are
designed to deal with internal and external
parasites. Today only three major anthelmintic families are used in Canada: endectocides, benzimidazoles and imidazoles.
Over the past dozen years, it has become
evident that many of the modern anthelmintics, upon which the cattle industry relies on
for effective disease control, have begun to
show diminished efficacy.
Increasing resistance means producers
using the same ectoparasite products are
finding them less effective.
A 2012 Canadian study of roundworms
found that Ostertagi was the dominant species of internal parasite causing production
losses in mature cows. Ostertagia has been
shown to alter immune system response to
vaccines. One third of Alberta farms did not
respond well to treatment with ivermectin,
meaning it could no longer guarantee the

removal of all round worms.
With no new, effective products on the
horizon livestock managers need to develop
best management practices to offset growing
resistance.
Frequent use of the same anthelmintic
drug class is a considerable risk factor in
building resistance. Low doses, instead of
full, can have the same effect. Producers
are encouraged to alternate between drug
classes and methods of application as well as
ensure the correct dosage.
Producers developing a program should
keep in mind the concept of a regime developed to totally suppress parasites may not be
the best approach, as it tends to accelerate
development of resistance. A realistic program that keeps the parasite population at
an economically acceptable level, will extend
producer efficacy and maintain profitability
in the long run.