ACTIVITY OF FENBENDAZOLE AGAINST INHIBITED EARLY 4TH-STAGE LARVAE OF OSTERTAGIA-OSTERTAGI

Abstract

The efficacy of fenbendazole against inhibited early 4th-stage larvae of O. ostertagi and other nematodes of the abomasum and intestinal tract was investigated in naturally infected, yearling cattle in April 1978. The time when peak levels of inhibited larvae occurred was determined by epizootiologic study which began in Nov. 1977. All animals were removed from pasture and maintained free from further helminth infection until slaughter (19-21 days). The fenbendazole liquid suspension was administered as an oral drench at dose level of 10 mg/kg to 10 animals and then at dose level of 15 mg/kg to an additional 10 animals at 10 days after removal from pasture. Eleven animals were maintained as untreated controls. In cattle given the dose of 10 mg/kg, the following reductions were observed: O. ostertagi adults, 100%; developing stages, 80%; inhibited larvae, 97%; and other worm genera in the abomasum and nematodes of the intestinal tract, 100%. In the cattle given the larger dose, the following reductions were observed: O. ostertagi adults, 100%; developing stages, 98%; inhibited larvae, 99%; and other worm genera in the abomasum and nematodes of the intestinal tract, 100%.