A Simulation Approach for Evaluating Management Decisions for Grassland-based Beef Production Systems in the Low-altitude Region of Kyushu : Land Use, Animal Density and Target Liveweight Gain

Abstract

A simulation approach was made to evaluate management decisions for grassland-based beef production (growing cattle) systems in the low-altitude region of Kyushu. Two hundred scenarios which differed in land use, animal density (AD, 2-10 head/ha), target liveweight gain (TLWG, 0.2-0.8kg/head/day) and sex of animals (steers and heifers) were tested using data from a case farm. The land was utilized as a forage crop field (FCF), a permanent pasture (PP) or their mixture. A variety of agroecological and economic criteria were used for evaluation. As an example of the quest for optimal management for a given goal, scenarios for a sustainable system were searched for. Three scenarios were finally selected as most appropriate, but they were not regarded as sustainable because of their high potential N impact on the environment. The similar management options among the 3 scenarios (proportion of FCF area=0.5-0.75, AD=6 head/ha, TLWG=0.4kg/head/day) reflected the trade-off between the FCF and PP, and this was considered to be one of the central issues in many grasslandbased animal production systems of the region.