The objective of the present study was to propose the use of protein free diet (PFD) associated with synthetic amino acids (AA) as method to determine the amino acid and protein endogenous loss in broiler chicks, as the normal endogenous flux is underestimated in PFD use. Eighty-four Ross 308 male chickens were used, aged from 17 to 22 days in a randomized complete design, totaling two treatments with six replications, with seven birds per experimental unit. The endogenous amino acid losses were determined from the results of the analyses. No difference was observed in the endogenous losses of protein and amino acids in broilers fed with PFD+AA or PFD, except for the nonessential amino acid cystine (0.216 × 0.162 mg/g Dry Matter Intake, DMI) and serine (0.432 × 0.356 mg/g DMI), that was greater in birds fed with PFD+AA than in those fed PFD, respectively. With the exception of lysine, tryptophan, arginine, leucine and histidine, all other amino acids were lost in a considerable amount when the birds received PFD+AA. In both diets, the amino acids with lowest losses were methionine (0.087 and 0.096 mg/kg DMI) and tryptophan (0.079 and 0.066 mg/kg DMI) and the greatest losses were threonine (0.481 and 0.600 mg/kg DMI) and acid glutamic (0.623 and 0.648 mg/kg DMI). The use of PFD+AA is an alternative method to the use of the protein-free diet to determine the endogenous loss of amino acids in broiler chickens.
digestibility; metabolism; physiology; protein; protein free diet; synthetic amino acid
