Sixty-five sheep flocks were studied in Santa Catarina State to determine parasites resistance to anthelmintics based on ivermectin (0.2mg/kg), levamisole (10mg/kg), closantel (10mg/kg) and albendazole (10 mg/kg). The evaluation was carryed out when a particular sheep flock showed a control group with EPG (eggs per gram) level above 500. Larvae culture was also performed to allow the parasite identification. Four randomized groups of 10 animals were formed and treated with one of the four anthelmintic products. Faecal samples were collected of each group seven to ten days after the treatment, aiming to perform the eggs count and larvae identification. These results were compared with results of the control group. The anthelmintics were considered to present evidence of parasite resistance when the efficacy of the product was lower than 95%. From the total of 65 sheep flock studied, seventy-seven percent presented parasite resistance to ivermectin, with Haemonchus larvae only (100%); sixty-five percent to albendazole, with Haemonchus (74%), Ostertagia (15%) and Trichostrongylus (11%); thirteen percent to closantel, with Haemonchus (100%); and fifteen percent to levamisole, with Thichostrongylus (44%), Ostertagia (39%) and Haemonchus (17%). The results detected the presence of a multi-resistance to anthelminthics in the great majority of the sheep flocks of Santa Catarina State.
Keywords: Anthelmintics, nematodes, resistance, sheep.