ChileanJAR

A mathematical model, with estocastic variability in function of animal feed intake, was developed. It simulates three different extensive beef production systems, based in continuous grazing. The principal management decisions (initial herd structure, herd reproductive and management data, sward fertilization, feed supplementation, and animal purchasing and selling management) that can affect the system, are inputs of the model. Forage availabil ity and nutritive value in each field are actualized weekly, according to amount of old and new material, which determines animal feed consumption. Liveweight changes, within each animal category, are estimated through the energy and protein balances. Animals are changed to another category, according to physiological status or age. A summary, containing meat and forage production/ha and average stocking rate in each field, is generated at the end of each.simulated year. The model was validated using experimental data from the Cauquenes Exp. Sta. (INlA, Chile). The maximum differences between model and experimental weight gains were 11.5%, for cows, and 0.2%, for calves, in the raising system, and 1.9%, for steers, in the beef production system.