Persistent efficacy of doramectin pour-on against artificially induced infections of nematodes in cattle

Two studies were conducted to determine the persistent efficacy of doramectin pour-on against an artificial, trickle challenge of mixed nematodes in calves. In each study, 42, 4-8 months old calves were randomly assigned into four groups of 10 animals each (T1-T4), plus two larval-viability monitor animals. All animals were treated with fenbendazole (10 mg kg(-1)) 14 days prior to the start of the study to clear any existing infection. Doramectin pour-on at 500 mu g kg(-1) was used on each animal in Groups T2, T3, and T4 with intervals of 1 week (Day 0, 7, and 14, respectively). Calves in Group T1 were treated with saline solution on Day 0 and at the same volumetric rate (1 mi 10 kg(-1)) as the doramectin treated animals. All treatments were applied in a single passage along the midline of the back, from the withers to the tailhead. Subsequently, trickle inoculations with infective larvae were administered to all calves for 22 consecutive days (Days 14-35), Doramectin pour-on provided greater than or equal to 91.9% efficacy against challenge with Dictyocaulus viviparus, Haemonchus spp., and Ostertagia, ostertngi for up to 35 days post-treatment anh against challenge with Cooperica ancophora, Cooperia punctata, and Oesophagostomum radiatum for up to 28 days post-treatment. (C) 1999 Elsevier Science B.V. All rights reserved.