Nemabiome metabarcoding of wild conservation bison herds and co-grazing cattle reveals different species compositions and low-level benzimidazole resistance

Gastrointestinal nematodes (GIN) live in complex communities within American plains bison (<i>Bison bison</i>), a keystone ungulate species of North American prairie ecosystems. These trichostrongylid nematode species vary in their level of pathogenicity and can cause disease ranging from subclinical to clinical. However, the GIN species diversity and distribution of North American bison are understudied, especially in conservation herds in the United States. Fecal samples from conservation bison were collected from six herds in 2022, with five of those herds resampled in 2023 across six states (Colorado, Iowa, Nebraska, North Dakota, South Dakota, Oklahoma). Fecal samples from a herd of longhorn cattle that co-graze with a bison herd from Oklahoma were also collected in both years. Following fecal egg counts and coproculture, third-stage larvae were processed using ITS2 rDNA metabarcoding to determine the trichostrongylid species composition and screened for the 200Y (TTC > TAC) polymorphisms of the isotype-1 β-tubulin gene to assess possible benzimidazole resistance. Alpha diversity was determined for each herd using the Shannon and the inverse Simpson diversity Index. The Beta diversity was assessed between herds using the Bray-Curtis dissimilarity index. The three most common species found were <i>Haemonchus placei</i>, <i>Ostertagia ostertagi</i>, and <i>Cooperia oncophora</i>. The herds with the highest parasite species diversity were in Oklahoma, Iowa, and North Dakota. The herd in Colorado showed the least diverse parasite communities. Over the course of the two-year study, moderate to high GIN species diversity was observed across several of the conservation bison herds. Additionally, different parasite species proportions were determined between co-grazing bison and cattle herds. Lastly, low frequencies of the 200Y (TTC > TAC) polymorphisms, associated with benzimidazole resistance, were detected. Our study reveals differences in species diversity and richness among conservation bison herds across the United States and provides the first evidence of benzimidazole resistance markers in wild bison in North America.