The objective of this study was to determine the protein requirements of Zebu sterrs grazing grazing five Bracharia decumbens paddocks. Twenty-seven steers averaging initial body weight (BW) of 311.0 kg and 14 months old were used. Three animals were slaughtered after the adaptation peiod to serve as reference for the estimate of empty body weight (EBW), and the initial body composition of the animals kept in the experiment. Among the 24 remaining animals, four were placed in the maintenance group, with restricted grazing time. The other 20 were allotted to four treatments: mineral mixture, self-feed and two feeding frequencies (three times a week, Monday, Wednesday and Friday, or daily. The net protein requirements for gain decreased as body weight increased. The protein requirement detected for an animal with 250 kg BW was 153.71 g/kg EBW, while for an animal of 400 kg live weight it was 141.86 g/kg EBG. The following equation was obtained to estimate the retained protein (RP) in function of the fasting live weight gain (LWG) and the retained energy (RE): RP = -34.6109 + 257.956*LWG – 17.01*RE. The metabolizable protein requirements estimated for maintenance and gain were 357.77 and 288.33 g/kg BW, respectively, for a 400 kg BW grazing steer. The animals fed protein supplementation presented greater degradable protein requirements in the rumen than non-supplemented animals, due the greater intake of total digestible nutrients (TDN). For an animal with 400 kg BW fed protein supplementation, the daily requirements for degradable protein in the rumen and non-degradable protein are, respectively, 764.22 and 73.89 g that corresponded to a crude protein requirement of 838.10 g/day.
crude protein; pasture; requirements; zebu cattle
