Efficacy of moxidectin pour-on against gastrointestinal nematodes and Dictyocaulus viviparus in cattle.

Twenty crossbred beef heifer calves were used for an efficacy evaluation of 0.5% moxidectin pour-on against gastrointestinal nematodes and Dictyocaulus viviparus. The latter parasite and Bunostomum phlebotomum were the target species. The calves were exposed to natural infection on pasture from late September to December 22. Additionally, all calves were experimentally infected with B. phlebotomum at 71 and 29 days before treatment and with D. viviparus at 29 days before treatment. The 20 calves were randomly allocated into two groups of ten, based on presence of patent lungworm and hookworm infections on days -6 and -1. Treatments were as follows: Group A, moxidectin 0.5% pour-on (PO) at 500 micrograms kg-1 BW; Group B, moxidectin vehicle (controls) by PO application. General strongyle and hookworm egg counts and lungworm larval counts were reduced to zero at 13 days after moxidectin treatment; treatment effect was significant (P < 0.05) only for the strongyle and hookworm counts. Percentage reduction for adult hookworms and mature-immature adult lungworms was 100.0 and also for adults and L4 Haemonchus placei and Ostertagia ostertagi and Trichostrongylus axei adults, adult males of Cooperia pectinata and C. spatulata, and Oesophagostomum radiatum adults. Efficacy values for C. punctata adult males, Cooperia spp. adult females, and Cooperia spp. L4 were > 99.9%, > 99.9%, and 92.4%, respectively. All efficacy values were significant (alpha = 0.05, 1-sided) except for Cooperia spp. L4.