Evidence for multiple anthelmintic resistance in sheep and goats reared under the same management in coastal Kenya

Four experiments, two with sheep and two with goats, were carried out to determine the efficacy of ivermectin, fenbendazole, levamisole, closantel and some of their combinations by faecal egg count reduction tests. In the first experiment, injectable ivermectin, oral ivermectin, fenbendazole and levamisole were tested in 6-month-old lambs, and their reduction percentages were 77 percent, 13 percent, 42 percent and 92 percent, respectively. In the second experiment, with yearling sheep, the reduction percentages were 35 percent for injectable ivermectin, 32 percent for fenbendazole, 99 percent for levamisole, 48 percent for closantel, 92 percent for injectable ivermectin combined with fenbendazole, 99 percent for injectable ivermectin combined with levamisole, and 100 percent for fenbendazole combined with levamisole. In the study with 18-month-old goats given the same does rates as those recommended for sheep, the reduction percentages were 73 percent for injectable ivermectin, 25 percent for fenbendazole, and 78 percent for levamisole. another group of 14-month-old goats was treated with does rates 1.5 times those recommended for sheep and the reduction percentages were 93 percent for levamisole, 92 percent for injectable ivermectin, and 97 percent for a combination of levamisole and ivermectin. In all experiments with sheep and goats the gastrointestinal nematode parasites identified by larval cultures were Haemonchus contortus, Trichostrongylus spand Oeso-phagostomum spThe gastrointestinal nematodes of both sheep and goats on this farm are resistant to ivermectin and fenbvendazole, whereas levamisole is still effective in sheep, but not in goats. The results are discussed in relation to the farm as a source of breeding stock to smallholder farmers and its potential to spread anthelmintic resistance.