The importance of subclinical parasitic gastroenteritis (PCE) in terms of reduced productivity has recently been recognised, and this has caused attention to be focussed on prevention of infection as opposed to cure. The process of strategic treatment with anthelmintics and movement to fresh grazing proposed by Michel (1969), has been superseded by the need for preventative measures based solely upon anthelmintic control, rather than strict grazing rotation, and in response to this demand several systems have been developed.

In this trial the efficacy of a controlled release bolus containing albendazole, Captec, (Smith Kline Animal Health, Ltd., CSIRO) against gastro-intestinal nematode infections in first season calves was evaluated, the nematode challenge being monitored using untreated control calves.

2 groups of 20 heifer calves of approximately 9 months of age at turnout, were grazed from May to October on separate, adjacent paddocks obtained by splitting a single field which had been grazed by cattle the previous autumn. The allocation of calves to each group was such that the mean liveweight and range of liveweights within each group were similar. At turnout each calf in group A received a Captec bolus, group B being untreated controls. Total numbers and species of infective larvae present on the pasture were monitored throughout the grazing period. The calves were weighed and samples were regularly collected for the determination of faecal egg output, serum pepsinogen and plasma gastrin concentration. Post mortem worm burdens were assessed in 7 calves per group on day 100 after turnout, and again in 3 calves per group 1 week after housing.