Abstract:
Animal production in Australia EFFECT OF STOCKING RATE AND YEAR ON SEASONAL LIVEWEIGHT GAINS OF STEERS GRAZING PERENNIAL PASTURES P.R. BIRD*, M.J. WATSON* and J.W.D. CAYLEY* Seasonal effects on liveweight change (LWG) of cattle are well tropical pastures (Edye et al. 1978) but are not well documented for pastures. Nor is it widely appreciated that the Jones and Sandland relating a linear depression in LWG to increasing stocking rate (SR) hold for the spring grazing season on temperate pastures. known on temperate (1974) model does not The data in Table 1 is from a replicated SR experiment with Hereford weaner steers, described by Bird et al. (1978). The year was divided into two periods corresponding with autumn-winter (Feb-late Aug) and spring-summer (Sept-mid Jan). The usual pattern of pasture growth is a small autumn peak, a marked winter low, an increase from late Aug to a peak in mid Nov, and senescence from Dee-Feb. TABLE 1 Liveweight gains (kg/hd) and compensatory gains (%) of steers f- Data for the autumn-winter period indicate a linear relationship between SR and LWG/hd, as there is for the annual cycle (Bird et al. 1978). However, there is a curvilinear relationship during the spring period, due to compensatory growth of steers restricted during winter at higher SR. This compensation is variable and accentuated in years when the spring period is prolonged by late rains, as in 1978. At the optimum SR most or all of the annual LWG was made during spring and greater emphasis should be given to more effective use of spring pastures. BIRD, P.R., CAYLEY, J.W.D. and WATSON, M.J. (1978). Proc. Aust. Soc. Anim. Prod. 12:216. EDYE, L.A., WILLIAMS, W.T. and WINTER, W.H. (1978). Aust. J. Agric. Res. 29:103. 83:1335. JONES, R.J. and SANDLAND, R.L. (1974). J. Agric. Sci., Camb. * Pastoral Research Institute, Hamilton, Vic. 3300. 467