Short Communications Influence of drench volume on the disposition of oxfendazole in sheep

THERE has been considerable discussion regarding the procedure of oral drench administration to ruminants with the potential for oesophageal groove closure or rumen bypass to influence drug availability. Using a glucose marker techhique, Prichard and Hennessy (1981) demonstrated that approximately one-third of sheep drenched with oxfendazole (oFz) formulation at 22-65 g/litre (Systamex; Syntex Animal Health) exhibited reduced drug availability due to complete rumen bypass and approximately one-third of the treated sheep exhibited a partial rumen bypass. Because it is the duration of exposure that is a significant determi-nant of benzimidazole action (Lacey and others 1987), the reduced oFZ residence time in sheep which displayed rumen bypass was reflected in lower anthelmintic efficacy. Similar reduced benzimidazole availability, attributed to oesophageal groove closure, has been reported in cattle (McEwan and Oakle