Survey finds routine bison deworming often outpaces testing
Bottom line
Most ranched bison producers in a new U.S. survey said they deworm at least once a year, but few reported using fecal diagnostics or refugia strategies first, a pattern researchers say could speed anthelmintic resistance in gastrointestinal nematodes. The study, published in Veterinary Parasitology and led by Texas A&M investigators, surveyed 79 producers from 15 states and found 87.3% dewormed annually, nearly one-third treated in both warm and cool seasons, and fewer than 10% intentionally left animals untreated to preserve refugia. Researchers also found that dosing was often imprecise, with only 34.8% of respondents reporting weight-based dosing, while many operations relied on visual estimates or herd averages. (pubmed.ncbi.nlm.nih.gov)
Why it matters: For veterinary professionals working with bison herds, the findings reinforce a familiar stewardship problem in a less-studied species: treatment is common, but diagnostic guidance is not. Texas A&M researchers said bison producers often adapt cattle protocols even though parasite control in bison has important handling, pharmacologic, and management differences, and only one product is FDA approved for gastrointestinal nematodes in bison. That matters because prior Texas A&M work found high frequencies of benzimidazole-resistance–associated mutations in parasites from 16 ranched bison herds in Texas and Oklahoma, suggesting resistance pressure is already more than theoretical. USDA’s Bison 2022 report points in the same direction at the industry level, finding just 23.2% of operations performed laboratory fecal testing for intestinal parasites, while 46.2% to 50.9% in some regions reported rotating dewormer types to deter resistance, a practice livestock parasitologists have increasingly moved away from as a standalone resistance strategy. (today.tamu.edu)
What to watch: Watch for bison-specific parasite-control guidance, broader U.S. surveillance on resistance patterns, and whether more herds shift toward fecal testing and targeted selective treatment. (today.tamu.edu)
Key facts
- Study type
- Survey of bison producers
- Journal
- Veterinary Parasitology
- Lead institution
- Texas A&M
- Sample size
- 79 producers
- States represented
- 15 states
- Annual deworming
- 87.3% dewormed at least annually
- Refugia use
- Fewer than 10% intentionally left animals untreated
- Weight-based dosing
- 34.8% reported dosing by individual body weight
- FDA-approved product
- Only one product is FDA approved for gastrointestinal nematodes in bison
A new Veterinary Parasitology survey is putting numbers behind a growing concern in bison medicine: many producers are deworming routinely, but relatively few are using diagnostics to decide when treatment is needed. In the study, led by researchers at Texas A&M, 79 producers from 15 states reported parasite-control practices that were largely drug-centric, with 87.3% deworming at least annually and nearly one-third treating more than twice a year. The authors say those patterns may increase selection pressure for anthelmintic resistance in ranched bison herds. (pubmed.ncbi.nlm.nih.gov)
The backdrop is a species that’s commercially important, but still understudied compared with cattle. Texas A&M noted that many bison operations use management approaches adapted from cattle production, even though bison can be harder and riskier to handle, making repeated chute work less practical. The same researchers also said the evidence base for ideal drug dosing and treatment strategies in bison remains limited, which complicates efforts to use dewormers precisely and sustainably. (today.tamu.edu)
The survey’s details help explain why researchers are concerned. Macrocyclic lactones and benzimidazoles were widely used, often in rotation or combination, and 28.1% of respondents who answered that question said they administered multiple dewormers simultaneously. Only about one-third reported dosing based on individual body weight, while fewer than 10% said they intentionally left some animals untreated as refugia, a core resistance-management concept meant to preserve a susceptible parasite population. Although about two-thirds of respondents said they had moderate-to-high concern about internal nematodes and anthelmintic resistance, the study found that fecal egg counts, fecal egg count reduction tests, and targeted selective treatment were rarely used in routine practice. (pubmed.ncbi.nlm.nih.gov)
That survey lands after earlier Texas A&M work raised the alarm on resistance itself, not just management risk. In a 2025 Texas A&M report on ranched herds in Texas and Oklahoma, researchers said they found resistance-associated genetic mutations in parasites from all 16 herds sampled, with average relative frequencies around 68% in Ostertagia ostertagi and 70% in Haemonchus contortus and H. placei. Some samples showed even higher levels. Verocai said at the time that the findings mattered not only for bison, but also for other ruminants, because parasite transmission between species is plausible where operations share pastures or management systems. (stories.tamu.edu)
Researchers’ public comments around the new survey were practical rather than alarmist. Verocai said fecal testing can help determine whether treatment is necessary and may ultimately reduce drug use and cost, while also slowing resistance pressure. Kipp emphasized the long game, arguing that refugia needs more attention if parasite-control programs are going to remain sustainable over five, 10, or 20 years. Those comments align with the study’s conclusion that bison-specific, evidence-based guidance is still needed. (today.tamu.edu)
Why it matters: For veterinarians, the study sharpens an emerging stewardship issue in food animal and mixed practice settings that include bison. If most herds are still treated on a calendar schedule, often with estimated rather than measured dosing, and with little routine fecal monitoring, resistance management becomes harder at exactly the moment drug options are limited. Texas A&M said only one product is FDA approved for gastrointestinal nematodes in bison, which means extra-label adaptation from cattle remains common. That leaves veterinarians in a key role: building herd-specific protocols around fecal testing, treatment thresholds, handling realities, and client education on refugia and targeted selective treatment, rather than default whole-herd deworming. (today.tamu.edu)
The broader industry context suggests this isn’t just a small-survey outlier. USDA’s Bison 2022 study found that 75.0% of operations used some dewormer from July 1, 2021, through June 30, 2022, but only 23.2% performed laboratory fecal testing for intestinal parasites. Among operations that did test, private veterinarians handled the majority of fecal testing most often, underscoring how central veterinary access and workflow may be to changing practice. Taken together, the federal data and the Texas A&M survey suggest there’s room for veterinarians to move parasite control in bison toward the same diagnostic-driven stewardship framework increasingly emphasized in other ruminant species. (direct.aphis.usda.gov)
What to watch: The next signals to watch are whether Texas A&M’s work expands into broader national resistance surveillance, whether bison-specific dosing and control recommendations begin to formalize, and whether producers adopt more routine fecal testing before treatment decisions are made. (today.tamu.edu)