Since 1940, the papers published in scientific journals reported that grazing is the most economic way to feed cattle in Brazil. During the wet season continuous growth of animals is observed, but in the dry season there is almost no weight gain or the weight gain obtained in the wet season is lost. During the dry season the high indigestible fibre content of tropical pastures and the very low crude protein intake are the main factors for the weight loss. When forage availability is too low, an energetic supplement must be given, because protein supplements alone do not overcome the energetic demands. Urea is a nitrogen feedstuff of the lowest cost available in Brazil and is source of N-NH₃ for rumen fibrolytic microorganisms which use ammonia for growth. The economic aspects of supplementation during the wet season have so far not been investigated in Brazil. When cattle receive supplements containing large amounts of NaCl (150 - 300 g kg^-1), the animals exhibit a constant pattern of nutrient intake from the supplement, go frequently to the trough and consume more water than non-supplemented animals. Although much research has been done, and positive effects for animal growth and improvement of herd reproductive parameters were confirmed, there has been no investigation on the reduction of phosphorus supplementation when cattle are fed with protein-energetic supplements. Finally, farmers and extension workers should know that the response of animals to protein-energetic supplementation is established by Mitscherlich's law; e.g. non-linear growth and decreasing performance as supplement intake increases.