LINEAR AND NON-LINEAR MODELS OF NUTRIENT UTILIZATION TO FORMULATE DIETS FOR RUMINANTSThe costs of beef cattle production were estimated for: 1) least-cost diets (DCM) formulated using traditional linear programming; and 2) maximum-profit diets (DLM) formulated using a non-linear program based on the Cornell Net Carbohydrate and Protein System adjusted to Brazilian conditions. The proposed model (RLM - 1.0) minimizes the cost per unit gain while attending energy, protein, and mineral requirements. The production costs were simulated using diets programmed through both methods (DCM and DLM). Performance parameters for the animals, carcass selling prices, feed composition and feed prices were representative of those available at three different states in Brazil. The DCM diets had 68% of TDN and 13% of protein, typical of brazilian feedlot diets. The DLM diets converged by the program had higher TDN values and consequently higher rates of gain were attained. Although the daily cost per animal was higher for DLM diets, cost per unit gain was lower as compared to DCM. This difference was greater with decreasing concentrate prices. In conclusion it is recommended that diets should be formulated using non-linear programming systems, which are capable of simulating growth and corresponding nutrient requirements. Least-cost tools should be used with caution in different production environments.
least-cost diets; maximum-profit diets; ruminants