Anthelmintic activity of paste and drench formulations of oxfendazole in horses

Oxfendazole was administered in paste or drench formulations to groups of five horses carrying naturally acquired worm burdens. At a dose rate of 10 mg/kg the efficacy of either formulation appeared similar. One hundred per cent of the adult populations of the following genera was removed: Parascaris, Oxyuris, Strongylus (S edentatus, S vulgaris), Triodontophorus and Trichostrongylus axei. Efficacy against adult small strongyles, adult Habronema microstoma and immature Oxyuris equi was in the region of 96 to 99 per cent. The level of efficacy against immature small strongyles was at least 74 to 75 per cent, against fourth stage larvae of S vulgaris in the mesenteric arteries between 83 and 88 per cent and against fourth stage S edentatus in flank lesions between 97 and 99 per cent. Early fifth stage sheathed S vulgaris larvae in arteries were less susceptible. The drug failed to remove very young parascaris and habronema and had no effect against Anoplocephala perfoliata and various instars of Gasterophilus intestinalis and G nasalis. Hatching tests on strongyle eggs passed in the faeces indicated that 24 hours must elapse before all become sterile.