A simulation modelwas developed and validated with the objective of evaluating and predictingthe productive performance of steers with different weights and initial ageskept on Panicum sp. or Brachiaria sp. cultivated pastures in tropicaland subtropical regions. The model established the direct relationships betweentwo main components (animal and fodder plant) and two indirect components (climateand soil). The animal component included: intake of forage dry matter, supplementintake, stocking rate, initial weight and age of the animals, biotype (adultweight and weight at birth), energy requirement for maintenance and production(live weight gain). The forage components included: growth, senescence, digestibilityand availability. The results obtained with the model were compared to thoseobtained in the literature under similar conditions in Brazil and a low percentageof estimated error was found (35%). The model is an adequate tool to evaluatecertain nutritional strategies and thus to assist in decisions that depend onthe weight gain of the animals and pasture conditions over time.
