Hence, the objective of this work was to evaluate decreasing levels of crude protein (CP), without altering theratio of essential amino acids, in free-range broiler chickens. Two experiments were conducted, which evaluated broiler chickens during the growing (43 to 56 days, Experiment 1) and finishing (57 to 70 days, Experiment 2) periods. A total of 630 males chickens of the Colonial lineage were housed in 30 boxes (21 chickens/box), with shelter area and paddocks. A completely randomized design composed of five treatments and six repetitions was used. The levels of CP tested were: 17.5, 17.0, 16.5, 16.0 and 15.5%, and 17.0, 16.5, 16.0, 15.5 and 15.0% for growing and finishing periods, respectively. The performance traits, carcass and cutsyield, and meat quality were evaluated. No effect of CP levels on the performance traits was found in broilers evaluated in two periods. Lower hot and cold carcass yield, and higher b* values in chickens were observed at the levels of CP of 16.26, 16.25 and 15.81%, respectively. However, the higher b* values may be a result of the higher corn gluten concentration in the diet. When the ideal ratio between amino acids and lysine is met, it is possible to reduce the levels of dietary CPin free-range broiler chickens down to 15.5 and 15.0% in the growing and finishing periods, respectively, without leading to a decreased performance, and carcass and cutsyield.
amino acids; carcass yield; ideal protein; low-protein diet
