The application of a simulation model to control strategies in ovine gastro-intestinal parasitism.

A simulation model which describes the pattern of increase in Ostertagia circumcincta infective larvae on pasture grazed by ewes and lambs, was used to test the effect of anthelmintic treatment at different times in the grazing season. Treatment generally resulted in a delay in the rise to peak larval count, and marked differences were recorded in two successive years, which were related to a combination of time of treatment and weather conditions.