Persistent activity of doramectin injectable formulation against experimental challenge with Haemonchus placei in cattle

Two studies were conducted in North America to evaluate the persistent acti vity of doramectin injectable formulation against experimental challenge wi th Haemonchus placei. In both studies, calves were randomly assigned to 1 o f 4 treatment groups (n = 10 per group) or a larval viability group (n = 2) . Calves were treated subcutaneously in the lateral midline of the neck wit h saline (1 ml/50 kg) on Day 0, or with doramectin (200 mg/kg = 1 ml/50 kg) on Day 0, 7, or 14. Animals used to assess larval viability did not receiv e any treatment. Beginning on Day 14 and continuing through Day 28, each of the 40 treated calves were given approximately 300 infective larvae of H. placei per os. The two larval viability animals received approximately 10,0 00 larvae as a single dose on Day 28. Approximately two weeks later, all an imals were slaughtered and the abomasum from each calf processed for nemato de recovery. A 2% aliquot of abomasal contents plus wash was examined for e numeration and identification of nematodes. Geometric mean H. placei counts were calculated from the log (H. placei count + 1) and used to estimate pe rcentage reduction. Overall, doramectin was greater than or equal to 96.9% efficacious in reducing infection with H. placei when challenged daily 14-2 8 days after treatment. (C) 1999 Elsevier Science B.V. All rights reserved.