Survey of management practices related to parasite control from ranched North American bison (Bison bison) in the southern United States.

Anthelmintic resistance (AR) in gastrointestinal nematodes (GIN) is an emerging concern in grazing livestock, including the North American bison (Bison bison). Nevertheless, little is known about routine parasite control practices in ranched bison herds. This cross-sectional survey of bison producers in 22 states across the southern and central United States characterized herd demographics, pasture management, nutrition, animal sourcing, and anthelmintic use. Seventy-nine producers from 15 states responded, most managing herds on fewer than 300 acres. Parasite control was predominantly drug-centric: 87.3% (69/79) dewormed at least once annually, 31.6% (25/79) treated in both warm and cool seasons, and nearly one-third dewormed more than twice per year. Macrocyclic lactones (ivermectin: 65.7%, moxidectin: 29.9%) and benzimidazoles (fenbendazole: 50.8%, albendazole: 28.4%) were widely used, frequently in rotation or combination; 28.1% (18/64) administered multiple dewormers simultaneously. Only 34.8% (23/66) dosed based on individual body weights, while most relied on visual estimates or herd averages, and fewer than 10% (7/70) intentionally left animals untreated as refugia. Although 64% (46/72) and 65% (47/72) reported moderate-to-high concern (≥3/5), about internal nematodes and AR, respectively, routine diagnostics (fecal egg counts, fecal egg count reduction tests, targeted selective treatment) were rarely employed. These findings reveal that intensive whole-herd deworming, minimal diagnostics, and limited refugia are common within the US bison industry, likely increasing selection pressure for AR and underscoring the need for bison-specific, evidence-based, diagnostic-driven parasite control guidelines and education.