Effect of grazing management on minimising effects of parasitic nematodes on lamb production

An integrated management system involving cattle, ewes and lambs developed to minimise levels of parasitic nematode contamination of pasture was evaluated in a 2-year (1989-1991) study. Four experimental farmlets were managed as self-containcd units over a May-May year. Over the two years, stocking rate averaged 15 su/ha and cattle:sheep ratio 35:65. Three treatments (lambs regularly drenched, ewes drenched post-lambing/ lambs undrenchedand undrenchedewes andlambs) were similarly managed (set-stocked, lambing to weaning, 7-day shifts post-weaning, a 77-day interval between consecutive lamb grazings and a strict rotation of lambs followed by ewes with cattle midway between the ewe and subsequent lamb grazing). A fourth treatment differed in each year: in year 1, lambs were set stocked over summer and in year 2 cattle followed lambs, and ewes were positioned mid-way in the rotation between lambs and cattle, In both years, the management system developed to minimise nematode parasitism in lambs mamtained low levels of infective larvae on pasture (~80 L3 larvae/kg pasture), and a faecal egg count in lambs of less than 1500 epg; clinical parasitism was not observed. However, regular anthelmintic drenching of lambs significantly (P~0.01) increased liveweight gain of lambs from weaning in November to May by an average 35% over the 2 years. In year two, grazing ewes ahead of lambs significantly increased (PcO.01) pasture larvae levels and lamb faecal egg counts and decreased liveweight gain compared with grazing cattle ahead. Drenching ewes to minimise effects of the post-parturient rise in faecal egg count had no influence on nematode levels in lambs or on lamb performance.