Effectiveness of the most often used anthelmintic molecules on digestive nematodes in sheep

Anthelmintic resistance (AR) is an increasing problem globally. Antiparasitic strategies that rely mainly on chemical molecules are increasingly threatened by the emergence of parasite strains resistant to numerous classes of anthelmintic substances. Benzimidazoles, imidazothiazoles, and macrocyclic lactones are the most frequent classes of broad-spectrum anthelmintics used against sheep nematodes. Multiple resistances are increasingly being reported for these compounds. In 2022, we performed a study in a herd from Cluj County, Romania, aiming to evaluate the efficacy of four anthelmintic synthetic molecules [albendazole (ABZ), levamisole (LEV), eprinomectin (EPR) and doramectin (DOR)]. Faecal samples were collected, before and 14 days after the treatment. The faecal egg count reduction test (FECRT) was used and coprocultures were performed for each group. Third-stage larvae (L3) were collected after 10 days from coproculture and identified using morphological and morphometrical keys. Before the treatment, we identified 5-6 strongyle genera/species in each group. Haemonchus contortus was the most resistant species. The population of digestive strongyles found in the herd under study showed resistance to all four used molecules; only the therapeutic combination consisting of levamisole and doramectin had efficacy > 95%. For Strongyfollowing the administration of doramectin, eprinozole + doramectin and levamisole + doramectin.