Contrasting Isotype-1 β-Tubulin Genotypes at Benzimidazole-Resistance Loci in Haemonchus contortus from Yining and Tacheng, Northwestern Xinjiang, China

Benzimidazole (BZ) resistance in Haemonchus contortus constrains sheep production worldwide. Northwestern Xinjiang is an important livestock region, yet a parallel comparison of isotype-1 β-tubulin genotypes at the three canonical BZ-resistance loci has not been reported for Yining and Tacheng. Between July and August 2025, 148 adult male worms (77 from Yining and 71 from Tacheng) were collected from sheep processed at local abattoirs. Adult males were identified morphologically by the asymmetrical dorsal ray and the organisation of the bursal rays; females showed a barber-pole appearance. No other abomasal nematode species were observed in the examined material. Species identity of the 148 genotyped males was confirmed by ITS-2 PCR, with Sanger sequencing of 22 amplicons. Remaining males were identified by morphology only and were not subjected to molecular identification. A fragment of the isotype-1 β-tubulin gene spanning codons 167, 198 and 200 was amplified and Sanger-sequenced. Genotypes were coded SS, rS and rr. F167Y was absent from all worms. The two samples differed at E198A and F200Y. The Tacheng sample contained only heterozygous (rS) genotypes at these codons, with substitution-allele frequencies of 11.3% (E198A) and 13.4% (F200Y); SS genotypes predominated. The Yining sample contained rr genotypes at both codons, with higher substitution-allele frequencies (44.8% for E198A and 20.1% for F200Y) and more frequent co-occurrence of non-SS genotypes at the two codons. These findings provide a side-by-side molecular comparison of the two areas. Because sampling was abattoir-based, phenotypic assays were not performed, and individual treatment histories were unavailable, the results should not be read as confirmed clinical resistance or as a basis for region-specific drug protocols. They provide a baseline for further surveillance and for field efficacy testing of benzimidazoles in northern Xinjiang.