COUNTRY LIFE IN BC • FEBRUARY 2020


41


Researcher provides deworming tips for sheep Resistance to existing treatments places animals at risk


by BARBARA JOHNSTONE GRIMMER ABBOTSFORD – “The goal of a good parasite


program for sheep is to control parasites without allowing for the development of dewormer resistance,” University of Calgary professor Dr. Michel Lévy told the BC Sheep Federation conference in Abbotsford last fall. “It is a balancing act, involving the judicious use


of dewormers and the management of pastures.” Lévy has been investigating drug resistance of parasites with University of Calgary parasitologist John Gilleard since 2013. Their research has involved sheep producers from BC, Alberta, Saskatchewan and Manitoba to look at the prevalence of different worms and the effectiveness of deworming. The different species of worms present in fecal samples are identified using NevaBiome, a novel molecular technique that can identify the type of worm, since most worm eggs look the same. The study is determining parasitic resistance to dewormers in Western Canada. This work involves on-farm deworming assessments and a fecal egg count resistance test. The results to date have given producers insights into improved deworming


strategies. Resistance to existing vermicides has been increasing. New strategies could


extend the usefulness of these drugs and slow resistance to new drugs becoming available to producers. Drugs available are Ivermectin, Valbazen and Safeguard. Flukiver was


approved in 2017 for liver flukes and barber pole worm. Startect was approved in 2018. Levamisole was taken off the market in Canada, but it is still available in the US and can be compounded. “Drenches are best; injectables work fast but persist at low levels and will enhance resistance,” says Lévy. He recommends fasting the animals 24 hours before drenching to enhance absorption. He also says to avoid pour-on drugs because absorption is variable. Combination drugs have been in use in the US for the last four to five years.


“There is an additive effect of wormers, less


resistant worms, and a dilution of resistant worms on pasture,” says Lévy. Producers should do what they can to prevent


resistance from developing, he adds. “Use fecal egg count to check for resistance to


drugs. If you treat your sheep, you should see over 95% efficacy at two weeks,” he says. “If efficacy is less than this, you are developing resistance. Stop using that drug when resistance starts to show. The producer is the best one to judge if a dewormer is effective or not.” Lévy says that if you deworm everybody,


resistance happens faster. Producers should only deworm the sheep that need it. Treatments should be strategic and targeted. Reduced efficacy is not always due to resistance. Drench failure, an insufficient dose, underestimated


weight, faulty equipment or poor technique can all be factors. Out-of-date or poor-quality products may play a role. Take advantage of refugia, the practice of not treating some sheep so that


they have susceptible worms and increase the number of susceptible worms on pasture. Pasture management is critical as well. Pastures that were harvested hay


fields, ungrazed pastures, left idle for 90 days in summer or 180 days in fall and winter, are safe for grazing. He recommends reducing stocking rates and use rotation; leave land vacant; avoid grazing sheep, goats and llamas together; cograze with cattle or horses; or rotate species through the pasture. When producers buy new sheep, they should aggressively worm upon arrival, quarantine for 10 to 14 days and perform a fecal egg count to confirm that no eggs are shedding. Use new wormers on these sheep. “Use a cannon to kill a parasite,” says Lévy. ”Don’t buy resistant worms.” He advises working with a veterinarian to customize and implement control


programs that include components such as refugia, surveillance, treatment, effective drugs and best practices. As a professor of veterinary medicine, Lévy has encouraged veterinary students to take an interest in sheep and learn about them. “Having a vet interested in sheep is important,” he says.


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