Wanted: sheep manure, still warm.
Also wanted: sheep producers interested in parasite research.
Researchers John Gilleard and Michel Levy of the University of Calgary veterinary medicine faculty haven’t exactly placed a want ad, but they are trolling for more participants in an ongoing study of sheep parasites and their resistance to treatment.
Now in the fourth year of study, the researchers have found ever-higher levels of parasite resistance to anthelmintics, the treatments used to kill worms and other parasites in sheep.
They’ve drawn that conclusion after studying fecal egg counts in manure samples sent in by producers and through on-site data gathered by the research team.
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“Overall it’s actually quite unusual to find completely effective treatment on those samples that producers are sending in,” said Gilleard.
“You actually see, in the majority of the cases, less than 100 percent reduction in egg counts.”
Ivermectin (Ivomec) and fenbendazole (Safe-Guard) are the two most common products used by producers and they’ve been in use for years. Gilleard said on-site tests by researchers show the products are becoming less effective as parasites develop defences against them.
In fact, he said only a couple of farms studied so far have not developed resistance to those products.
The study includes tests of Levamisol and Cydectin, both used in the United States, and little resistance has been found. That is also true of Flukiver, which is registered in Canada but is only effective against barber-pole worm.
Gilleard said a new Zoetis product called Startect, also approved for Canada, is part of research plans.
“We expect it to be very effective because it’s not been used here yet.”
Monitoring its use over a period of years will show how quickly resistance can develop, he added.
“Canada is in the fortunate position at the moment of having this new product coming on the market, which will help a lot, but of course it’s only a matter of time before that starts to go the same way.”
Most treatments used on sheep in Australia, New Zealand, Western Europe and the southern United States are already seriously compromised in terms of efficacy, Gilleard said.
In Australia and New Zealand, all treatments are a combination of three or four active ingredients and even so, they are not always completely effective.
It seems a losing battle against parasites’ ability to mount defences against treatment, but Gilleard said there are ways to mitigate parasite infection and resistance.
One is to graze larger areas more extensively and avoid heavy use of the same pastures. However, that’s not always possible. Another option is refugia, the practice of leaving some animals untreated so selection pressure on parasites, in which the most resistant parasites are more likely to survive, is reduced.
“That’s where a flock health plan factors in … to really try and minimize the amount of drug you used to use.”
Quite a few western Canadian sheep producers have helped with the study so far and Gilleard said more are needed to increase its scope and gather data that is more robust.
“The nice thing about having producers come back year after year is we can monitor all the time on the same farm. That’s a useful piece,” he said.
Producers with flocks of 20 or more sheep are needed. If interested, they can contact the researchers and once enrolled they will receive a package with an instruction sheet and all that is needed to gather and ship fecal samples.
The research group can be contacted at sheepstudy@ucalgary.ca.
