FORAGE QUALITY AND FEED-INTAKE RESPONSES OF CATTLE TO IMPROVED PASTURES, TREE KILLING AND STOCKING RATE IN OPEN EUCALYPT WOODLANDS OF NORTH-EASTERN AUSTRALIA

The effects of oversewing introduced grasses and legumes, tree killing and stocking rate on simulated diet quality and feed intake of cattle were studied in an open eucalypt woodland in the semi-arid tropics of north-eastern Australia in 1990. Rainfall during the experimental per iod was above average, producing good conditions for pasture growth, w hich resulted in little influence of stocking rate on pasture or dieta ry attributes. During the growing season, forage quality, as measured by nitrogen concentration and in vitro digestibility, was higher in so wn pasture than in native pasture, and higher in plots with live trees than in plots with killed trees. Treatment differences in herbage qua lity disappeared later in the year when pastures senesced. In sown pas ture treatments, there was no effect of tree killing on legume (Stylos anthes spp.) quality. However, Stylosanthes made a greater contributio n to the diet of cattle grazing in wooded paddocks than in paddocks wh ere trees had been killed. The proportion of Stylosanthes in the diet reached a peak in May and then declined. Oversewing increased both die t quality and feed intake while, to a lesser extent, killing trees res ulted in generally lower diet quality and feed intake. Estimates of li veweight change were made from the quantities of energy and protein co nsumed by the cattle. As expected, large increases in liveweight gain were predicted to occur in oversewn pastures compared with native past ures. However, estimates indicated that animal performance may be bett er where trees are left intact rather than killed. While carrying capa city is greatly increased with the removal of trees, this may be at th e expense of individual animal performance. Possible reasons for this significant negative response in dietary attributes and predicted live weight gain to tree killing are discussed.