Efficacy of topically administered doramectin against eyeworms, lungworms, and gastrointestinal nematodes of cattle.
The efficacy of topically administered doramectin against eye worms, lungworms, and gastrointestinal nematodes, was evaluated in 400 cattle (20 in each of 20 trials). Trials were conducted in North America and natural and experimentally induced infections were used. In each trial, cattle were allocated randomly to control (placebo or untreated; n = 10) or doramectin-treated (500 µg/kg of body weight; 10) groups. Treatments were applied in a single passage along the midline of the back, from the withers to the tailhead. Cattle were killed ≥ 14 days after treatment, and worm burdens were determined. Efficacy of doramectin was ≥ 95.3% against adults of Thelazia gulosa, T skrjabini, Dictyocaulus viviparus, Haemonchus contortus, H. placei, Ostertagia lyrata, O. ostertagi, Trichostrongylus axei, Bunostomum phlebotomum, Capillaria spp, Cooperia oncophora, C. pectinata, C. punctata, C. spatulata, C. surnabada, Nematodirus spathiger, Strongyloides papillosus, T. colubriformis, Oesophagostomum radiatum, and Trichuris spp. Efficacy was 95.1% against fourth-stage larvae of D. viviparus, H. placei, O. lyrata, O. ostertagi, T. axei, C. oncophora, C. punctata, C. spatulata, C. surnabada, N. helvetianus, T. colubriformis, O. radiatum, and Trichuris spp. In addition, efficacy against inhibited fourth-stage larvae of O. ostertagi and Ostertagia spp was ≥ 98.1%. It is concluded that a single topical application of doramectin pour-on was efficacious against a broad range of nematode species in cattle.