SMART: a Simple Model to Assess Range Technology

Abstract

A model, more detailed than a set of stocking rate response curves but less detailed than large process models such as SPUR, was needed to evaluate the short-term effect of grazing management practices on range herbage growth and livestock production. SMART (Simple Model to Assess Range Technology) simulates the effects of stocking rate and rotation on herbage production and steer performance. Herbage growth rate is a quadratic function of herbage biomass and is adjusted for seasonal differences. Herbage intake increases with herbage biomass and digestibility and animal weight. Animal gain increases logarithmically with digestible dry matter intake and decreases with animal weight. Output of these simulations confirms that early removal of steers from pasture in autumn will increase net returns, and that short-duration rotation grazing will produce little increase in gains or returns over those achieved under season-long grazing. Development of the SMART model revealed deficiencies in our understanding of the factors controlling herbage intake.