Long-term parasitological consequences and production responses in ewes and lambs after a single post-parturient anthelmintic treatment of ewes

Abstract

A study was made of the long-term parasitological and production consequences of a post-parturient (docking) anthelmintic treatment for spring-lambing ewes given about 3 weeks after the mean lambing date. During summer, treated and untreated ewes continued to graze their respective pastures which were subsequently grazed by lambs during the autumn and winter. Faecal egg counts of the treated ewes were significantly lower than those of untreated controls throughout spring and summer. In the lambs, there was no significant difference in the mean egg counts at weaning. On all sampling occasions in autumn and winter, mean faecal egg counts of lambs on pasture previously grazed by treated ewes in summer were lower than those of lambs on pasture grazed by untreated ewes. The difference was significant on 50% of the sampling dates. Maximum larval availability on pasture grazed by the treated ewes was respectively 78, 58, and 35% lower in summer, autumn, and winter than on pasture grazed by the untreated controls. Treated ewes and their lambs were 3.3 and 0.8 kg heavier respectively at weaning than the controls. During summer, treated ewes produced 0.18 kg more wool. During the autumn-winter period, the lambs grazing pasture previously grazed by the treated ewes showed mean liveweight gain and greasy fleece production advantages of 1.5 and 0.15 kg respectively. Although possible paddock interaction was not measured, the trend of parasitological parameters suggests that the production responses recorded can be largely attributed to the treatment. Both the parasitological and production consequences of the post-parturient parasite burdens in ewes may therefore be more extensive than has been demonstrated previously. The data also illustrate an important, practical correlation between the decrease in the levels of residual dry matter on pasture over winter and an increase in the availability of infective larvae to the grazing animal.

Keywords:

• trichostrongylid nematodes
• anthelmintics
• ewes
• lambs
• post-parturient drenching
• larval availability
• liveweight gain
• wool production