Lack of efficacy of topical administration of eprinomectin against gastrointestinal nematode in a French dairy sheep farm: A case of underexposure of worms

Resistance to eprinomectin was suspected in a dairy sheep farm southwestern France. The efficacy of topical and injection formulations against gastrointestinal nematodes (GINs) compared using faecal egg count reduction test. GIN species were identified by real-time PCR, concentrations measured serum High-Performance Liquid Chromatography 2 5 days after treatment. Efficacies 99.6% 86.1% for formulations, respectively. Before treatment, the three Haemonchus contortus, Teladorsagia circumcincta Trichostrongylus colubriformis both groups. After H. contortus T. group only. Two above ng/ml under this value group, suggesting underexposure latter group. High levels exposure are important avoid loss field.