Anthelmintic resistance of gastrointestinal nematodes in cattle herds in mid-mountain central France

Abstract

Anthelmintic resistance (AR) in gastrointestinal nematodes is insufficiently studied in cattle in many European regions, including France, where only three studies have been conducted in the north-west. This study evaluated the efficacy of benzimidazoles and avermectins in cattle from a mid-mountain region in central France. Faecal egg count reduction tests (FECRT) were performed in 22 groups of 10–25 calves from 16 dairy or beef farms. Each group received either oral oxfendazole (OFZ, 11 groups) or injectable ivermectin (IVM, 11 groups). Faecal samples were collected in a paired study design before (D ₀ ) and after treatment (D _10-14 for OFZ, D _14-17 for IVM). Individual faecal egg counts (FECs) were determined using the Mini-FLOTAC method, and pooled faecal samples were cultured per group to determine the proportions of Ostertagia and Cooperia larvae using droplet digital PCR. Efficacy classification (resistant, susceptible or inconclusive) was determined for each group according to the WAAVP guidelines, using the fecrt.com web application and the clinical protocol scenario with a grey zone of 90–99%. IVM resistance was detected on 10 of 11 farms, with 33–49% and 51–67% of larvae being Ostertagia and Cooperia after treatment, respectively. The remaining farm had inconclusive results. OFZ resistance was detected on 2 of 11 farms, with 100% and 97% of larvae being Ostertagia after treatment. The remaining 9 farms were classified as susceptible. This study provides valuable local insights into AR, which could help raise awareness among farmers and veterinarians and encourage changes in treatment practices.