Study finds resistance to de-wormers in Ontario beef cattle
By Lilian Schaer for Livestock Research Innovation Corporation
Gastrointestinal nematodes, also known as roundworms, are common in beef cattle, mostly spread orally on pasture. In small ruminants like sheep and goats, anthelmintic resistance – resistance to de-worming products – is a significant problem, and University of Guelph researchers suspected this might also be a problem in Ontario beef herds.
Dr. Jessica Gordon, veterinarian and Assistant Professor in Ruminant Health Management, headed up a trial to learn more about the issue in Ontario cattle and how widespread it might be.
“Parasitism in cattle doesn’t often cause death the way it does in small ruminants, but it will affect production,” she explains. “The animals won’t grow as well, won’t breed as well, will be on the thinner side and their calves won’t be as healthy at birth; that’s why we de-worm. And when de-wormers don’t function properly, we see these problems come back in.”
Parasites need grass to complete part of their life cycle so in a cold climate like Canada where fresh grass doesn’t grow year-round, there is a least part of the year where there is no transmission.
Part of Gordon’s research included determining whether those parasites can overwinter in the field and re-emerge the following year, contributing to resistance issues. Mature cows can also carry the parasites in their gut, and excrete the eggs onto pastures in the spring where other animals can pick them up.
In a trial at the Elora Research Station, Gordon followed three groups of cows over two years: those not treated with de-wormer, those treated with commonly used pour-on Ivermectin, and those treated with a newer de-worming fenbendazole product.
They evaluated every cow’s body condition score, weight and calf performance, including weight while nursing, as well as taking fecal egg counts every month. Gordon found that while the control animals had higher fecal egg count numbers than the de-wormed cattle, there was little difference between them when economic performance measures were looked at.
Researchers did find evidence of resistance to Ivermectin, as well as fenbendazole, which was unexpected.
“The interesting thing for us was that we saw evidence of resistance to Ivermectin, but we also saw evidence of resistance to fenbendazole, which is the first time this has been identified in cattle in Ontario,” Gordon said.
“This is a pilot project in only one herd at the research station, but considering the fact that these cows are de-wormed only once in their life, it is surprising to see resistance to both of the products, especially one they hadn’t seen before our trial,” she added.
Pending funding approvals, Gordon is hopeful another de-worming trial, this time involving stocker cattle, will start this coming summer to look for evidence of resistance on commercial farms.
“We went into this thinking we had a resistance problem in Ontario in cattle, but to find resistance to a de-wormer we rarely use was surprising,” she said. “It does suggest that there is likely resistance in the commercial herd as well.”
Once resistance is present in a herd, it’s nearly impossible to get rid of but it can be managed. She advises producers to speak with their vet about testing their herds for parasites and follow up with targeted de-worming of particularly vulnerable animals. This includes first calvers, thinner animals, or yearlings coming off pasture.
The last extensive parasite work done in commercial beef cattle in Ontario prior to Gordon’s project was completed in the 1970s, which means there aren’t currently good measures on what the economic impact of resistance could be on a beef operation.
The project was funded by Beef Farmers of Ontario and the Ontario Farm Innovation Program.
This article was published in Ontario Beef, May 2019. It is provided by Livestock Research Innovation Corporation as part of LRIC’s ongoing efforts to report on Canadian livestock research developments and outcomes.