Field studies on the seasonal incidence of Nematodirus battus and N. filicollis in sheep

The seasonal incidence of Nematodirus infection in sheep was followed by faecal egg counts, post-mortem examination and pasture larval studies. 2. It was shown that only one generation of adult worms was produced each year and that the life history required a prolonged resting stage on the pasture, which took 12 months to complete. 3. The influence of this type of life cycle on the parasitic disease caused by Nematodirus , and on its control, are discussed.