Epidemiological Studies on Gastro-intestinal Nematode Parasites of Sheep: Infection Patterns on Clean and Summer-contaminated Pasture

Abstract

SUMMARY The pattern of infection with gastro-intestinal nematodes in ewes and lambs on clean and autumn-contaminated pasture has been followed by faecal egg counts and pasture larval counts, and lamb weight gains and post-mortem worm counts were also recorded. No overwintering of larvae occurred from the autumn contamination. On clean pasture the ewe ‘spring rise’ in April–May was followed by a pasture larval peak in July, causing a wave of infection in the lambs in August–September. This pattern did not involve a period of multiplication in the lambs by re-infectiou, and it is suggested that not more than 2 generations of parasites occur in the lambs during the grazing season. Dosing the ewes resulted in a statistically significant reduction in lamb egg count, lower worm burdens and increased weight gains in the lambs, but was not associated with lower pasture larval counts.