FIELD-EVALUATION OF A FENBENDAZOLE SLOW-RELEASE BOLUS IN THE CONTROL OF NEMATODE INFECTIONS IN FIRST-SEASON CATTLE

The efficacy of a fenbendazole slow release bolus in controlling nemat ode infections of first-season cattle was evaluated in a field study i n northern Germany, Two groups, each of 11 male calves, were set-stock ed on separate pastures from May until October 1989 (157 days). The an imals of one group were given the bolus at turnout and the animals of the control group were treated with fenbendazole (7.5 mg/kg bodyweight ) eight weeks after turnout, Clinical inspections and measurements of faecal egg and larval counts, herbage trichostrongyle larval counts, p lasma pepsinogen concentrations and bodyweight were made throughout th e study, All the animals were slaughtered for worm counts and the eval uation of carcase quality two weeks after housing, The pasture grazed by the control group showed a marked increase in trichostrongyle larva e from late August onwards and, as a result, the control calves had in creasing faecal egg counts and increased plasma pepsinogen concentrati ons in the latter part of the grazing season, although no clinical sig ns of parasitic gastroenteritis were apparent, The fenbendazole slow r elease bolus suppressed the trichostrongyle infections during the graz ing season, and larval counts on the pasture grazed by the bolus-treat ed group remained low throughout the study. Postmortem examination sho wed that the bolus-treated calves harboured significantly (P<0.01) few er trichostrongyle worms, including inhibited stages, than the control s, Because of an inadequate lungworm challenge during the grazing seas on it was not possible to evaluate the efficacy of the fenbendazole sl ow release bolus in preventing parasitic bronchitis, At slaughter, the bolus-treated animals weighed more than the controls and tended to ha ve a better carcase quality.