Responses to the anthelmintic treatment of lambs at weaning: The relative importance of various sources of contamination in trichostrongyle infections

Abstract

Three trials were conducted in successive years to evaluate responses to a weaning anthelmintic treatment of lambs subsequently grazed on pasture contaminated with trichostrongyle larvae from different sources. The contamination deposited by ewes and lambs before weaning appears to be more important than residual overwintered infection or that arising from lambs after weaning. An appreciable live-weight-gain advantage resulted from the anthelmintic treatment when it was accompanied by the removal of animals to “safe” pasture. However, when lambs were not moved the response to drenching was small. A move to safe pasture at weaning, without anthelmintic treatment, provided a response similar to or better than anthelmintic treatment alone. The results suggest that earlier New Zealand studies have considerably underestimated the importance of trichostrongyle worm infection in lambs during the early post-weaning (summer) period.