Anthelminthic resistance of bovine nematodes against ivermectin in two farms of the south of Chile

Abstract

Anthelminthic resistance of bovine nematodes against ivermectin was determined in two farms in the south of Chile: one of them located near Purranque (Farm 1) and the other near San Pablo (Farm 2), in which 14 and 22 bovines aged 7 to 8 months were treated with 0.2 ml/kg of ivermectin, respectively. Faecal samples were obtained from each animal 7 days before and 21 days after the treatment to carry out the faecal egg count reduction test (FECRT). A 90.3% of egg count reduction was found in Farm 1, with Trichostrongylusand Cooperia as the most resistant genera. In Farm 2 there was 73.5% of egg count reduction, with Nematodirus as the most resistant genera followed by Cooperia and Trichostrongylus. It was concluded that there was anthelminthic nematode resistance to ivermectin in Farm 2, while in Farm 1 resistance was gradually appearing.