Field efficacy of moxidectin 0.5% pour-on against Chorioptes bovis, Damalinia bovis, Linognathus vituli and Psoroptes ovis in naturally infected cattle.

Field efficacy of a pour-on formulation of moxidectin, a macrocyclic lactone endectocide, was evaluated in cattle naturally infested with Chorioptes bovis, Damalinia bovis, Linognathus vituli and Psoroptes ovis. In trial 1, two experimental groups of cattle naturally infested with P. ovis were formed. Group 1 animals remained as untreated controls whereas Group 2 animals were treated on day 0 with 0.5% moxidectin cattle pour-on at a dose of 0.5 mg kg-1 bw. Efficacy was assessed by (a) taking skin samples from each animal on days -4, 7, 14, 21, 28, 42 and 56 post treatment (PT) and observing the numbers of viable P. ovis mites and (b) clinical examination of animals on days 7, 14, 21, 28, 42 and 56 with the percentage of affected body surface calculated and live body weights recorded for each animal on days 4, 28 and 42. The pour-on formulation of moxidectin yielded excellent efficacy as no live mites were found in treated animals at 14, 21, 28, 42 and 56 days PT, except in one animal from which one adult mite was collected on day 42. Clinical indices showed a regular decrease in the affected body surface area. All untreated animals but one remained positive until day 28 and their clinical condition worsened rapidly. In trial 2, two experimental groups of cattle naturally infested with D. bovis and L. vituli were selected. Group 1 remained as untreated controls whereas Group 2 individuals were treated on day 0 with 0.5% moxidectin cattle pour-on at a dose of 0.5 mg kg-1 bw. Efficacy was assessed by identifying and counting lice on eight 15 cm hair partings at predefined anatomical sites on days 0, 14, 28 and 42. On the basis of animals cured and lice count reduction, efficacies were 100% on day 14 and from then onwards for both species. In trial 3, 24 animals naturally infested with C. bovis were divided into three experimental groups comprising eight (Group I), seven (Group 2) and nine animals (Group 3). Group 1 was the untreated control group whereas Groups 2 and 3 animals were treated on day 0 with 0.5% moxidectin cattle pour-on at a dose of 0.25 mg and 0.5 mg kg-1 bw, respectively. Efficacy was assessed as in trial 1. Skin scrapings were collected on days -3, 7, 14, 28, 42 and 56 PT. A clinical index was calculated for each animal on days 0, 28 and 56 whereas body weights were recorded on days 0 and 56. At 0.25 mg kg-1 bw, the efficacy of moxidectin cattle pour-on against C. bovis was incomplete. In contrast, at a dose of 0.5 mg kg-1 bw, moxidectin cattle pour-on was fully effective and by day 14 PT all animals were negative for C. bovis and remained so until the end of the trial. No side effects were observed during these three trials. These results indicate that at a dose of 0.5 mg kg-1 bw, the pour-on formulation of moxidectin is highly effective against C. bovis, D. bovis, L. vituli and P. ovis.