Efficacy of albendazole against inhibited early fourth stage larvae of Ostertagia ostertagi.

Twelve untreated controls and 12 treated beef yearling steers were used in trials of albendazole (Smith Kline Animal Health Products) at 7.5 mg per kg (oral drench) against natural infections of inhibited fourth stage larvae of Ostertagia ostertagi. Albendazole had an efficacy of 83.8 per cent in removal of inhibited larvae. The mean number of inhibited larvae in untreated controls was 48.9 per cent. Efficacy against developing stages and adults of O ostertagi was 92.8 and 99.7 per cent, respectively. Efficacy against other worm genera in the abomasum, primarily thaemonchus and Cooperia adults, was 99.4 per cent. No signs of toxicity were observed following administration of albendazole. Some aspects of inhibition of O ostertagi in cattle in the USA are reviewed.