Pastures in Brazil represent almost 50% of the arable area and about 80% of them are cultivated with species of the genus Brachiaria sp. Modelling is a useful tool in predicting forage mass and weight gain by cattle and can be applied in the management of pasture (rate of occupancy, height of pasture and cutting frequency) and animals, from the knowledge of soil variables, climate, and animal behavior, affected by variables linked to morphology and structure of the forage canopy and food supplementation practices.