EFFICACY OF INJECTABLE ABAMECTIN AGAINST GASTROINTESTINAL-TRACT NEMATODES AND LUNGWORMS OF CATTLE

Efficacy of abamectin against gastrointestinal tract nematodes and lun gworms of cattle was determined in 4 experiments. The first 2 experime nts were controlled trials in which efficacy was determined at necrops y in calves with either experimentally induced (n = 14) or naturally a cquired (n = 16) infections. Half the calves in each experiment mere t reated with abamectin (200 mu g/kg of body weight, SC), and half were left untreated as controls. Efficacy Ras > 99% against adult stages of Dictyocaulus viviparus, Haemonchus placei, Ostertagia ostertagi, Tric hostrongylus axei, Cooperia punctata, Trichuris discolor, and C oncoph ora, and was 92.4% against Nematodirus helvetianus. The second 2 exper iments were clinical trials in which efficacy was determined by fecal egg count reduction in naturally infected yearling heifers (n = 75) or 2-year-old heifers (n = 75). Within replicates of 5, 4 heifers were a ssigned at random to treatment with 200 mu g of abamectin/kg and 1 was left untreated as a control. Abamectin was 100% effective in eliminat ing strongylate nematode eggs from the feces of these heifers. In all experiments, adverse reactions were limited to small, clinically unimp ortant injection site swellings in 29% of abamectin-treated calves. Ab amectin was judged to be safe and effective in these trials.