Benzimidazole Resistance of Donkey Gastrointestinal Nematodes in Xinjiang, China, Assessed by the Faecal Egg Count Reduction Test and 18S r2b Amplicon Sequencing

Abstract

Gastrointestinal nematode (GIN) infection constrains equid production, and benzimidazole (BZ) resistance is widespread. Xinjiang is a major donkey-breeding region of China, yet anthelmintic-resistance data for donkeys are scarce. This study combined a faecal egg count reduction test (FECRT) with 18S r2b amplicon sequencing in female donkeys aged 1.0 and 1.5 years on one large-scale farm. Faecal samples from 74 animals were screened by the McMaster method; 30 with more than 150 eggs per gram (EPG) were enrolled and allocated to an albendazole-treated group (n = 15) and an untreated control group (n = 15), with counts on Days 0, 7 and 14. Overall, 63.51% (47/74) were excreting nematode eggs; strongyle-type eggs occurred in 62.16% (46/74) and Parascaris spp. eggs in 2.70% (2/74). The Day-14 group-level FECR was −24.49% (90% CI −93.56 to 19.93), far below the 99% target efficacy for benzimidazoles in equids, so the population is classified as resistant. No effect of treatment over time was detected when the control group was included in the models. Sequencing assigned almost all reads to a single genus, Trichostrongylus, and no cyathostomin genus was recovered; the 18S r2b marker resolves the strongyles of equids poorly, so these results are exploratory and species-level identification will require a different marker.