A field evaluation of anthelmintics for control of cyathostomes of horses in Brazil

Abstract

The anthelmintic efficacy of ivermectin (IVM), piperazine citrate (PPZ) and fenbendazole (FBZ) alone, and combinations of FBZ with varying dosages of PPZ, was evaluated for the control of strogyles of Mangalarga equids. In all cases of positive strongyle egg counts per gram of faeces (EPG) before and after treatment, pure populations of cyathostome larvae with eight gut cells were consistently observed in faecal cultures. The faecal egg count reductions (FECR) were evaluated between Day 7 and Day 56 post-treatment. Significant differences ( P⩽0.05) were found between Day 7 and Day 49 when comparing the mean EPG values of IVM with those of the other anthelmintics. PPZ alone and the combination of FBZ (7.5 mg kg −1) and PPZ (55 mg base kg −1) did not show significant differences during the trial; both groups exhibiting an FECR of > 90% between Day 7 and Day 30. Horses treated with the combinations of FBZ (7.5 mg kg −1) and PPZ at either 40 or 25 mg base kg −1, and with FBZ alone at either 7.5 or 15 mg kg −1, showed an FECR of <90% 2 weeks after treatment. The emergence of a degree of resistance of strongyles to FBZ and PPZ in a segment of the cyathostomes in this population is suggested.