The first survey of parasite control on bison ranches shows most herds are dewormed on a schedule, with little testing to see whether they need it. Researchers say the habit could make resistance harder to manage.
Most US bison producers deworm their herds at least once a year, and many do it more often. Very few check first to see whether the animals need it. That's the main finding of a new Texas A&M University survey. The researchers say the pattern could increase pressure for drug resistance in a species with only 1 FDA-approved treatment for gastrointestinal nematodes.
The study, published in Veterinary Parasitology, is the first survey of parasite control practices in ranched North American bison (Bison bison).1 Researchers surveyed 79 producers across 15 states in the southern and central United States. Whole-herd deworming on a set calendar was the norm. Two of the core tools for managing resistance, fecal diagnostics and refugia, were largely missing.
“Gastrointestinal nematodes are one of the most economically important health concerns for bison,” lead author Kaylee Kipp, PhD, said in a university news release.2 “We have both anecdotal and diagnostic evidence showing that bison seem to have more parasitic issues compared to beef cattle.” Kipp earned her doctorate at the Texas A&M College of Veterinary Medicine and Biomedical Sciences (VMBS). She is now an associate professor of ranch management at Texas Christian University.
Heavy gastrointestinal nematode burdens in bison can cause diarrhea, poor weight gain, and reduced productivity. In severe cases, they can contribute to the death of adult animals.2
The survey found a lot of treatment and not much testing1:
The findings point to a gap between concern about resistance and use of practices that can help manage it.1
Part of the problem is that bison producers have limited options. Many borrow protocols from the cattle industry, and those protocols don't always fit bison.
“There is only one product that is FDA approved to treat gastrointestinal nematodes in bison,” said senior author Guilherme Verocai, DVM, MSc, PhD, DACVM (Parasitology). He is an associate professor in the VMBS Department of Veterinary Pathobiology and director of its Parasitology Diagnostic Laboratory.2
Handling is another obstacle. Bison are challenging and dangerous to work with, so rounding them up for frequent hands-on treatment isn't realistic. Some producers give dewormers in medicated feed instead, according to the release.2
Verocai warned that repeated deworming without diagnostic testing to guide it gives resistance a chance to build.2
“The concern is that over time, we could reach a point where the majority of those parasites are resistant,” Verocai said.2
The researchers point to diagnostics as one way to make treatment decisions more targeted. Fecal testing can help estimate parasite burdens and help determine whether treatment is warranted. With that information, producers can treat selectively instead of dosing the whole herd.
“What might look like extra labor—collecting the fecal sample, sending it to the lab, and waiting on those results—most likely means you would treat fewer animals and save money on drug use,” Verocai said.2
Refugia is the other main strategy. Leaving part of the herd untreated maintains a population of drug-susceptible parasites, which can reproduce alongside resistant parasites and help slow the increase of resistance in the population. Kipp said refugia deserves more attention and that using it well means planning further ahead than most producers do now.
“We can't only be thinking about the next growing season, the next breeding season, or the next calving season,” Kipp said.2 She added that producers need to think 5, 10, or even 20 years out.
She also flagged biosecurity as an overlooked risk when new stock arrives. “Every time you buy an animal, you are buying parasites,” Kipp said.2
The authors conclude that bison-specific, evidence-based parasite control guidelines are needed rather than relying on approaches adapted from cattle.1
“It's a double-edged sword,” Kipp said.2 “Parasites can cause serious problems in bison, so the natural response is to deworm them, but more treatment isn't always better.”
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