The effect of ruminoreticulum bypass in yarded lambs on the efficacy of oxfendazole against resistant Trichostrongylus spp. helminths

An observational study was performed to investigate the effects of yarding and ruminoreticulum bypass on the efficacy of oxfendazole against resistant Trichostrongylus spp. helminths. Ruminoreticulum bypass was observed in 9- month old Perendale lambs using video-taped fluoroscopy and the efficacy of oxfendazole was estimated using the faecal egg count reduction test. Yardi ng and withholding feed for 24 h before drenching with oxfendazole signific antly enhanced the faecal egg count reduction for resistant Trichostrongylu s spp. parasites (p < 0.05), but ruminoreticulum bypass of the drench in th e yarded animals had no negative effect on anthelmintic efficacy (p > 0.05) . The effect of ruminoreticulum bypass on the efficacy of oxfendazole may d epend on the resistant parasite species present. The positive effects of ya rding sheep for 24 h before drenching, on the efficacy of oxfendazole again st resistant Trichostrongylus spp., probably outweigh any negative effects of ruminoreticulum bypass. However further studies are required, with diffe rent resistant parasite genera present, before firm recommendations can be made. (C) 2000 Elsevier Science B.V. All rights reserved.