Seasonal variations in pasture quality on New Zealand sheep and beef farms

Nineteen sheep and beef farmers in the Waikato, Tararua, Canterbury and Southland regions collected two pregrazing pasture samples offered to either lambs or bulls once every month from autumn 2000 to autumn 2001. One sample of pasture on offer was collected to ground level and the other was hand plucked to represent pasture selected by animals. The samples were analysed by NIRS for chemical composition and dissected into morphological components. Energy concentration of herbage was lowest in autumn and highest in spring. Energy concentrations of offered pasture were 8.1, 9.2, 7.6 and 10.0 MJME/kg DM in autumn and 10.3, 11.6, 10.8 and 11.4 MJME/kg DM in spring in Waikato, Tararua, Canterbury and Southland, respectively. Crude-protein, fibre and soluble-carbohydrate concentrations reflected the changes in ME. Variations in dead material and reproductive stem were the main causes of changes in ME. Predicted liveweight gain of 350-kg bulls grazing pasture with a pre- and post-grazing herbage mass of 2500 and 1500 kgDM/ha respectively, were 0.4, 0.8, 0.0, and 1.1 kg/d in autumn, and 1.2, 1.5, 1.4 and 1.6 kg/d in spring, for Waikato, Tararua, Canterbury and Southland regions, respectively. It is concluded that high animal performance in summer and autumn may not be achieved in summer-warm regions without the addition of high-quality forages or supplements.