The effects of grazing management systems on growth and nematode infections of beef cattle

Different grazing management systems were used in autumn and winter on the Tablelands of New South Wales to reduce parasitic infectivity of pastures. The grazing systems were: pasture ungrazed; pasture grazed by undosed adult cattle, by frequently dosed calves, or by sheep. Pasture infectivity was assessed by worm counts made on parasite-free tracer calves during spring, and on permanently grazing steers during summer and the following autumn. Also, liveweight gains of young beef cattle which were dosed and moved to prepared pastures in late July were compared with those of cattle grazing on pastures which had been contaminated by undosed calves. All the grazing systems resulted in reduced levels of pasture contamination with worm eggs, and lower worm burdens of Ostevtagia ostevtagi and other nematodes during spring and early summer. The effects of grazing systems were reflected in greater liveweight responses compared with those of cattle grazing contaminated pasture. Grazing with sheep or adult cattle and using ungrazed pasture produced significant gains of up to 57 kg head-l during spring and summer. In some Tableland areas, continuous grazing of prepared pastures from July to December led to clinical parasitism in summer. The results suggest that pastures were freshly contaminated during spring which, in turn, resulted in a massive increase in O. ostevtagi burdens during summer.