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Roundworm study may help form control plan

A three-year study at Agriculture Canada’s research centre in Lethbridge and at the University of Calgary will focus on roundworm resistance to ivermectin, and on the prevalence and better identification of the pests.

Livestock parasitologist Doug Colwell of Agriculture Canada and University of Calgary veterinarian and researcher John Gilleard will use fecal samples collected from Alberta cattle to develop molecular tools that will identify roundworm species.

They will use those tools to determine whether roundworm parasites that affect cattle productivity have become resistant to common treatments.

The research is funded through the Alberta Livestock and Meat Agency.

Ivermectin resistance has been found in other countries but no data is available for Canada, said Colwell. It could be a major issue for Canadian cattle producers, given that ivermectin is the “gold standard” in effective cattle nematode control.

“We simply want to know if it’s there,” Colwell said about ivermectin resistance. “It’s present in cattle parasites, cattle nematodes in other parts of North America, and we’d like to have a baseline … so we’ll be able to track it.”

Colwell said researchers want to avoid the problems that developed with ear tags infused with insecticide to control horn flies, which came into general use about 20 years ago. A resistance problem became evident when producers began complaining that the tags weren’t working.

“By then it was almost too late,” he said. “Now, with the nematodes, if we can be a little bit ahead of the curve, have a diagnostic tool ready, have some molecular tools ready, we can then be prepared to give advice to producers.

“If we don’t have (ivermectin resistance), it’s a good thing and we can make a plan. If it’s here already, then there’s some things we can do to kind of mitigate the problem and prevent it from getting any worse.”

However, before more detailed studies can be done, scientists must first find better ways to identify the different species of nematodes, or roundworms. Some are more economically damaging than others for the cattle industry.

Studies on roundworm prevalence depend largely on fecal egg counts, but eggs from different species look almost the same.

“There’s at least four species that all look very similar and some of them are more important than others, and we can’t, unfortunately, just by looking at them, tell what they are,” Colwell said.

Gilleard will take the lead in developing better identification tools, and through use of molecular speciation assays, he will assess ivermectin resistance in roundworms if any is found.

New imaging techniques will allow him to study large numbers of worms in a sample, speeding up data collection.

Fecal sample collection for the studies will be done at a feedlot near Nanton, Alta., which receives cattle from across Western Canada.

Researchers will take samples directly from young animals and track their origins to evaluate worm populations and species in various geographical regions.

At another feedlot, researchers will take fecal samples when cattle arrive and are treated with ivermectin. A second set of samples will be taken 14 to 21 days later and analyzed to gauge the effectiveness of the treatment.

“If there’s no change in egg numbers, we probably have a pretty good indication that there’s drug resistance out there,” Colwell said.

“If there’s no drug resistance, we should see somewhere between 80 and 95 percent reduction, because that drug should go in there and zap all the worms.”

Studies on ivermectin resistance are vital to the cattle industry, according to a background paper prepared by Colwell and Gilleard.

“In Alberta, the economic benefit of treating calves is well established. A large, peer-reviewed published study has shown a $7.04 per head benefit of treatment of calves against roundworms at feedlot entry,” the paper said. “A second study showed a $4.20 per head production benefit in yearlings.”

It said public research is required because “the pharmaceutical industry has not traditionally supported research into anthelmintic (endectocide) resistance and this is unlikely to change in the foreseeable future.”

Colwell said ALMA recently accepted a grant application to map western Canadian cattle roundworms using global information system techniques.

He believes a risk map can be created to help cattle producers identify problems by using roundworm data already collected and then factoring in soil type, moisture and other environmental data.

“Then we’d be able to forecast whether, based on changing environmental conditions, the nematode populations are going to be high or low in a particular area.”

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