Gastro-intestinal nematode infection in lambs — A model based on climatic indices for forecasting peak pasture larval contamination

Abstract

The parasiteOstertagia circumcincta is the primary cause of parasitic gastro-enteritis in lambs during their first season at grass. The life-cycle of this nematode parasite involves the development and survival of the free-living stages on pasture. Accordingly the pasture is the site of deposition, development and transmission of infection and meteorological factors affecting the pasture will affect the parasites. In this paper two empirical models for forecasting the timing of the “summer wave” of infective larvae on pasture are presented. These models are similar in form to that described by Starr and Thomas (1980) but involve different approaches to assessing the temperature and moisture components of the daily index value. Further, using the prediction model described by Paton, Thomas and Waller (1984) as an investigative tool, certain tentative suggestions are made as to a general fundamental weakness of empirical index methods.