When the bugs fight the drugs

Each summer DVM students from the Ontario Veterinary College at the University of Guelph delve into hands-on, practical experience at veterinary clinics across Ontario and additional locales during their Externship Veterinary Course. Funded by the Ontario Ministry of Agriculture, Food and Rural Affairs (OMAFRA), students must complete an eight-week Externship Course between third and fourth year in a rural veterinary practice that works with food animals and/or equine, as well as companion animals.These Externship blog posts are an opportunity to tag along with students this summer. Here student veterinarian Stephanie looks at anthelmintic resistance in sheep. Check out all the student blogs here.

Veterinary medicine is a constantly evolving field, with new pharmaceutical products being released every year. Drugs can play an important role in preserving the health of individuals and populations as a whole. However, they need to be used in a responsible and appropriate manner. In recent years the issue of drug resistance has become a hot topic. We will explore this complex problem by looking at anthelmintic resistance in sheep.

Sheep kept on pasture can become infected with various types of roundworms that live in the gastrointestinal tract. These parasites can cause a decrease in production and be detrimental to the sheep’s health. One parasite in particular, haemonchus contortus, also known as the ‘barber pole worm’, is highly pathogenic to sheep. It attaches to the inner lining of the stomach and feeds on blood, leading to anemia, edema (bottle jaw) and even death. Therefore, most farmers choose to deworm their flock with anthelmintics. This should lead to healthier sheep and higher production numbers, right? Not always.

The issue is that these gastrointestinal nematodes can evolve over time and no longer be affected by the dewormer, leading to overwhelming worm burdens in sheep. In a recent study on 47 Ontario farms, it was found that most farms had resistance to Ivermectin and fenbendazole, 2 commonly used anthelmintics in sheep. To make matters even more interesting, haemonchus contortus, the barber pole worm, was the main parasite responsible for the resistance. The question becomes: do we treat with a new class of drug that has a different mechanism of action, or do we change our current treatment protocols? The answer: we do both and more!

The Ontario Veterinary College and the Ontario Ministry of Food and Agriculture have come up with the 5 star worm plan that focuses on selective treatments as well as minimizing drug use and pasture contamination.

The goal of programs like this one is to promote proper drug use, maximize animal health and mitigate long term problems like drug resistance, ultimately being of benefit to the industry as a whole. It is evident that long-term, sustainable control of parasites in sheep requires integration of multiple control methods.

Through this brief overview of resistance to anthelmintics in sheep, it is important to be aware that drug resistance is a real issue affecting individual animals, to whole industries, and everything in between. The development of guidelines for prudent drug use in both the human and animal world are key to managing resistance. It is our duty as students, veterinarians, readers, members of the general public to stay educated on the matter of drug resistance. After all, it is the choices we make today that will shape our world of tomorrow.

Dr. Henry Ceelen and I are using the FAMACHA score on a ewe; the system estimates the degree of anemia in sheep through use of a color guided chart that is compared to the mucous membranes around the eye. FAMACHA can be used as an aid to determine which ewes require treatment, acting as part of “star 3” in the 5 star approach. Open communication and education of the producer is imperial to ensure that all 5 stars of the worm plan are covered. We are glad to have helped this farmer on the ongoing, ever-changing road towards a healthy flock.

Follow OVC on Twitter, Facebook, and Instagram @OntVetCollege

Comments are closed for this blog post

Welcome to
Ontario Agriculture

Sign Up
or Sign In

Agriculture Headlines from Farms.com Canada East News - click on title for full story

CAAIN receives $50 million from Ottawa

The federal government is investing in Canadian agriculture through technological innovation

Bunge to Present at Barclays Annual Global Consumer Conference

Bunge Global SA (NYSE: BG) today announced that company management will participate in a fireside chat at the upcoming 2026 Barclays Annual Global Consumer Conference on Tuesday, Sept. 8, at 3:00 p.m. ET. To listen to the live event, visit Bunge.com/events-and-presentations and click on the webcast link. A transcript and replay will be available for a limited time following the presentation. About Bunge At Bunge (NYSE: BG), our purpose is to connect farmers to consumers to deliver essential food, feed and fuel to the world. As a premier agribusiness solutions provider, our dedicated employees partner with farmers across the globe to move agricultural commodities from where they’re grown to where they’re needed—in faster, smarter, and more efficient ways. We are a world leader in grain origination, storage, distribution, oilseed processing and refining, offering a broad portfolio of plant-based oils, fats, and proteins. We work alongside our customers at both ends of the value chain

Bunge Reports Second Quarter 2026 Results

Bunge Global SA (NYSE: BG) today reported second quarter 2026 results Q2 GAAP diluted EPS of $3.47 vs. $2.61 in the prior year; $2.00 vs. $1.31 on an adjusted basis excluding certain gains/charges and mark-to-market timing differences Higher results primarily driven by strong performances in Soybean and Softseed Processing and Refining segments, supported by solid execution amid improving market conditions Repurchased ~$250 million of shares, completing the $2 billion program related to the Viterra transaction Increasing full-year adjusted EPS outlook range to $9.25 to $9.75 from $9.00 to $9.50 Overview Greg Heckman, Bunge’s Chief Executive Officer, commented: “Our team delivered another strong quarter, navigating a complex global environment with agility, focus and disciplined execution. Against a backdrop of geopolitical uncertainty and shifting trade flows, our expanded global platform did exactly what it was designed to do — capture opportunities and deliver for customers at both

U.S. livestock groups oppose proposed beef import plan

Four major U.S. agricultural and livestock organizations are urging President Donald Trump to reconsider a proposed plan that would allow additional beef imports over a 90-day period. The American Farm Bureau Federation, Livestock Marketing Association, National Cattlemen’s Beef Association and United States Cattlemen’s Association said in a letter released August 25, 2026, that they are concerned the proposal could have negative implications for U.S. cattle producers and the broader livestock sector. The groups said they support efforts to keep food affordable for consumers but are calling on the administration to work with industry stakeholders on policies that balance affordability with long-term producer viability and domestic food production. In the letter, the organizations argued that increased imports could put pressure on cattle markets and influence producer decisions related to herd expansion and investment. They also expressed concerns about the potential impact on the l

Saskatchewan professor honoured for beef research contributions

University of Saskatchewan researcher Dr. Bart Lardner has received the 2026 Canadian Beef Industry Award for Outstanding Research and Innovation. Lardner, a professor in the College of Agriculture and Bioresources and chair of the Saskatchewan Ministry of Agriculture’s Strategic Research Program in Cow-Calf and Forage Systems, is being recognized for more than 20 years of research focused on beef cattle management and forage production. His work has examined areas including winter grazing, water quality, forage management and heifer development, helping producers improve profitability while managing production costs. “Dr. Lardner’s research has helped producers reduce costs while maintaining performance and profitability,” said Dean Manning, Chair of the Beef Cattle Research Council. Manning said Lardner’s commitment to ensuring producers benefit from research investments, while supporting the next generation of researchers, is widely respected. Lardner has also supervised more th

More…

Badges | Report an Issue | Terms of Service