The results of a three#x2010;year study in New Zealand undertaken to compare the effect of alternating sheep and cattle grazing and of different pasture species on internal parasitism in lambs is reported. Despite the commonly held belief that the use of cattle in sheep production systems improves sheep health by reducing nematode burdens, this did not occur. Cattle substantially reduced pasture larval numbers. However, this failed to reduce parasite burdens in lambs as those managed in the absence of cattle apparently developed increased immunity to parasites in response to the greater larval availability. Varying the number of successive grazings by sheep or cattle from 1 to 4 did not change this result. Lamb carcass weights were improved by the presence of cattle, primarily because of improvements in pasture quality. Substituting 30 of the ryegrass area with lucerne or replacing ryegrass with a multi#x2010;species mix consisting predominantly of bromes, tall fescue, phalaris, timothy, and red and white clover, had no effect on lamb faecal egg counts or worm burdens. Lamb liveweight was not affected by herbage species. Both lucerne and the multi#x2010;species mix increased the requirement for conserved feed during winter compared with ryegrass#x2010;based systems.
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