This work, evaluated by means of an economically simulation, the beef production systems with heifers calving by first time at two ("one year" system), three ("two years" system) and four ("traditional" system) years old. In "one year" system, the female calves had three different nutritional systems during 100 days, after weaning in the first autumn/winter, constituted by one of the alternatives: a) continuous grazing on cultivated annual ryegrass - PAST; b) continuous grazing on natural pasture plus diet - CNR; c) feedlot, with sorghum silage plus urea - SIL. After 100 days, the heifers of the three alternatives grazed together on improved natural pastures. The models to compare the systems were constructed on an Excel spreadsheet, based on an original model. The biological data of "one year" system were collected at Guatambu Farm, Dom Pedrito, RS, of 395 beef calves. Annual gross margin was R$ 44.066,99, R$ 41.001,32, R$ 40.509,86, R$ 40.045,65 and R$ 14.148,08, respectively, for "two years", "one year" SIL, "one year" PAST, "one year" CNR and "traditional" beef productions systems. The variable cost was higher at "one year" CNR. Production systems using more intensifies technologies showed better results than the "traditional" beef cattle system.
age at first calving; beef cattle economicity; gross margin; production systems; variable costs
