FIELD EFFICACY OF INJECTABLE MOXIDECTIN IN CATTLE NATURALLY INFESTED WITH CHORIOPTES-BOVIS AND SARCOPTES-SCABIEI

Field efficacy of moxidectin, a macrocyclic lactone endectocide, was evaluated in cattle naturally infested with Chorioptes bovis and Sarcoptes scabiei. Eight animals were allocated to two groups of four animals each, based on parasitological and clinical status. Animals of the treated group received one subcutaneous injection of injectable moxidectin at 0.2 mg kg-1 body weight on Day 0. Individuals of the control group received emergency treatment of a single injection of moxidectin at 0.2 mg kg-1 body weight on Day 28. Efficacy was assessed by (a) taking skin samples from each animal on Days 0, 7, 14, 21, 28, 42 and 56 and observing the numbers of viable mite stages and species and (b) clinical examination of animals on Days 7, 14, 21, 28, 42 and 56 with the percentage of affected body surface calculated for each animal on Days 0, 28 and 56. On the basis of the geometric means from treated and control animals, the percentage reductions in the total numbers of living C. bovis mites on Days 7, 14, 21 and 28 were 69, 8 7, more than 99 and 98, respectively. However, at the end of the trial, only two animals were negative for C bovis. The percentage reductions in the total numbers of S. scabiei on Days 7, 14, 21 and 28 were 93, 1 00, 1 00 and 100, respectively. Clinical indices of the treated animals showed a sharp decrease in the affected body surface area from a mean of 43.6% on Day 0 to 0.9% and 0% on Days 28 and 56, respectively. The clinical condition of the controls worsened rapidly during the experiment (mean clinical index 37.5% and 81.6% on Days 0 and 28, respectively). All control animals were positive for both parasites on Day 28, when they were given an emergency treatment. Mean daily weight gains (DWG) were recorded in both groups; mean DWG values were extremely low in control animals (248 g day-1 vs. 723 g day-1 in treated animals). Treatment of the controls on Day 28 was associated with a sharp increase of mean DWG (1431 g day-1). No local or general side effects were observed.