Field efficacy of injectable and pour-on moxidectin in cattle naturally infested with Psoroptes ovis (Acarina: Psoroptidae)

Abstract

Field efficacy of moxidectin, a macrocyclic lactone endectocide, was evaluated in cattle naturally infested with Psoroptes ovis. Three groups of six animals were used based on parasitolgical and clinical status. Group 1 animals recieved one subcutaneous injection of injectable moxidectin at 0.2 mg kg −1 body weight; Group 2 animals recieved topically one dose of 0.5 mg kg −1 body weight of pouron moxidectin; Group 3 individuals remained untreated as controls. Efficacy was assessed by (a) taking skin samples from each animal on Days −4, 14, 28, 42 and 56 post-treatment (PT) and observing numbers of viable mite stages and species and (b) clinical examination of animals on Days 14, 28, 42 and 56 with the percentage of affected body surface calculated for each animal on Days −4, 28 and 56. Both formulations gave 100% efficacy as no live mites were foun d groups 1 or 2, 14, 28 and 56 days after treatment. Clinical indices showed a sharp decrease in the affected body surface area from a mean of 5.48% and 6.1% on Day −4 in Groups 1 and 2, respectively, to 0% in both groups on Days 28 and 56 PT. All untreated animals remained positive until Day 28. The clinical condition of the controls worsened rapidly during the experiment (mean clinical index: 2.87% and 13.05% on Days −4 and 28, respectively) and they were given an emergency treatment on Day 28. No side-effects were observed with either formulation. These results indicate that the pour-on formulation of moxidectin is as potent as the injectable one against severe P. ovis infestation in cattle, and this is in contrast to results obtained with other pour-on avermectins.