Field evaluation of doramectin for treatment of gastrointestinal nematode infections and louse infestations of cattle

Abstract

Objective - To evaluate the safety and efficacy of doramectin given by injection at a dosage of 200 μg/kg of body weight for treatment of gastrointestinal nematodiasis or louse infestations of cattle. Animals - 1,031 mixed-breed cattle were treated in the nematode study and 418 were treated in the louse study. Procedure - Naturally parasitized cattle were given 200 μg of doramectin/kg or an equivalent volume of saline solution, SC. In nematode experiments, fecal samples were collected from each animal 1 week before treatment, at time of treatment, and at weekly intervals thereafter for 3 weeks. In louse experiments, louse counts were carried out for each animal on the day of treatment and 14 and 28 days later. All cattle were weighed at the time of treatment and at the end of the experiment. Results - By 21 days after doramectin treatment, fecal egg counts had decreased to zero in 9 of 10 experiments and to 1 egg/g in the remaining experiment. Differences between treatment groups were significant (P < 0.0001) in all instances. Pretreatment coproculture identified Haemonchus, Ostertagia, Cooperia, Trichostrongylus, and Nematodirus as the represented genera. Doramectin was 100% effective in eliminating infestation with Linognathus vituli, Haematopinus eurysternus, and Solenopotes capillatus. Infestation with the chewing louse Damalinia bovis was reduced overall by 86%. For all species, posttreatment louse counts were significantly (P < 0.02) less for doramectin-treated cattle than for controls. Adverse reactions to doramectin were not apparent in either study. Conclusion and clinical relevance - Injectable doramectin at a dosage of 200 μg/kg is safe and effective for treatment of gastrointestinal nematodiasis and louse infestations of cattle under field conditions.