Efficacy of pour-on and injectable formulations of moxidectin and ivermectin in cattle naturally infected with Psoroptes ovis: parasitological, clinical and serological data.

On the basis of Psoroptes ovis counts performed on day -7, 32 animals were randomly allocated to a control group of five animals or to four groups comprising six or seven animals which were treated, respectively, with pour-on ivermectin (IPO), injectable ivermectin (II), pour-on moxidectin (MPO) and injectable moxidectin (IM). Living mites were counted in skin scrapings on days 0, 7, 14, 28, 42 and 56 post-treatment (PT). Lesions were recorded on a standardized map on days 0 and 56 PT. Antibody kinetics were studied using ELISA on serially diluted sera. The antibody titres were expressed as the dilution giving the positive/negative cut-off. Until their treatment on day 28, the control animals remained parasitologically positive and their antibody titres increased. In treated groups, all living mite counts were negative on days 28 and 42 PT but some animals were still infected on days 7 and 14 PT. On day 56, living P. ovis were found in one animal of the IPO group. An equation of regression describing the antibody decrease was calculated with each individual data set. In most of the treated animals, the coefficient of determination R2, which describes the closeness of fit to the linear model, was above 0.9. The linear model could not be applied (low R2) to the antibody kinetics of four animals: the day 56 positive animal and its two neighbours in the IPO group and one animal from the MPO group. In the treated groups, the differences between the numbers of infected animals, the mean daily weight gains or the mean antibody titres were not statistically significant. Mean daily weight gains of the treated groups were higher than in control animals.