Resistance of gastrointestinal nematodes to five different active principles in sheep infected naturally in São Paulo State, Brazil

Abstract

This study evaluated the efficacy of commercially available anthelmintic drugs by calculating the percent reduction of eggs per gram (EPGR%) and appropriate statistical tests. A total of 350 animals selected from five commercial sheep farms was divided in seven groups with 10 animals each: Group 1 - control, Group 2 - Albendazole (5 mg/kg); Group 3 - Levamisole hydrochloride (5 mg/kg); Group 4 - Ivermectin (0.2 mg/kg); Group 5 - Moxidectin (0.2 mg/kg); and Group 6 - Closantel (10 mg/kg); Group 7 - Ivermectin + Levamisole + Albendazole (200 mcg/kg Ivermectin, 7.5 mg/kg Levamisole and 5 mg/kg Albendazole). EPG percent reduction was determined between day zero and day 10 after treatment had started and compared between groups. It was observed that, practically, almost all the tested drugs had some level of parasitic resistance while Moxidectin was the most effective during treatment. The results show that more sustainable procedures such as pasture rotation system, plant‑based products, certain fungi and earthworms need to be adopted to reduce parasitism and anthelmintic resistance in ovine herds.