The climatic potential for beef cattle production in tropical Australia: Part II— liveweight change in relation to agroclimatic variables

Abstract

Part I of this series demonstrated a method of simulating a ‘green season’ and a ‘dry season’ which corresponded closely to the main period of liveweight gain and loss respectively of cattle on native grass pastures. This paper attempts to further characterise these seasons, using agro-climatic variables derived from a weekly pasture growth index, as to their quantitative relation to cattle liveweight changes. Neither the duration of the green season nor the variable most closely related to cumulative pasture growth (‘growth weeks’) accounted for much of the variation in amount of gain in the green season. In the dry season, however, the amount of liveweight loss was closely related to the estimated number of weeks without green feed (‘dry weeks’). Extraordinary weight loss in the dry season occurred in the years with few growth weeks in the green season, indicating pasture quantity as well as quality limitations in dry season nutrition in these years. In comparison to the green season, marginal response in liveweight to additional green weeks was over two times as great when cumulated over an entire year; this suggests that the main benefit of prolonging the green season is its effect in shortening the dry season. The problem of generalising from the very few stations with cattle data is discussed.