Epidemiological studies on Nematodirus species in sheep.

Faecal egg count and pasture larval studies on N battus and N filicollis in lambs showed distinct differences in epidemiology, the infective larvae of N battus hatching over a short restricted period in spring, whereas those of N filicollis show an extended period of hatching, beginning in autumn and increasing steadily through the winter to reach a spring peak. This difference was considered to be responsible for the much slower annual rate of increase recorded for N filicollis. Pasture infection with both species survived ploughing and reseeding, though in very small numbers, and one year's rest from sheep by alternate grazing with cattle proved equally effective in reducing the carryover of infection, and offered a practical method of controlling these species.