Therapeutic and protective efficacy of doramectin injectable against gastrointestinal nematodes in cattle in New Zealand: A comparison with moxidectin and invermectin pour-on formulations

Abstract

Two similar studies were conducted in New Zealand to compare the therapeutic and persistent activity of doramectin injectable, moxidectin pour-on, ivermectin pour-on and oxfendazole oral drench when administered to nematode-infected cattle which were then grazed on common pastures. On day 0 (treatment day), 40 cattle were weighed, faecal sampled and allocated on the basis of day −3 faecal egg counts (FEC) to four treatment groups. Cattle were then treated with either doramectin by subcutaneous (SC) injection, moxidectin and ivermectin by topical application, or oxfendazole orally using label-recommended dosages. Oxfendazole treatment served primarily as a control to monitor reinfection without persistent activity. Faecal samples for nematode egg counts and coprocultures for larval differentiation were collected six times between day 0 and day 56 and all cattle were reweighed on day 56. Doramectin reduced pretreatment FEC by 99.1% in the first study and by 100% in the second study when assessed at 14 days posttreatment. Corresponding reductions for moxidectin were 80.8% and 85.2%, for ivermectin 86.0% and 80% and oxfendazole 78.3% and 100%, respectively. Posttreatment rise in FEC indicated that reinfection of moxidectin-treated animals occurred at the same time as oxfendazole controls in both trials. Posttreatment rise in FEC with ivermectin pour-on was similar to moxidectin and oxfendazole in one study, but in the other study ivermectin pour-on delayed the rise by 14–21 days. The rise in FEC for doramectin was delayed for 14–21 days in one study and at least 21 days in the other. The better parasite control provided by doramectin resulted in greater weight gains for cattle over the 56-day period as compared to moxidectin pour-on, ivermectin pour-on and oxfendazole in both trials. Gains of doramectin treated cattle were significantly ( p < 0.05) greater than those of ivermectin and moxidectin groups in one trial and the oxfendazole group only in the other.