Amino acid requirements for pullets based on potential protein deposition and the efficiency of amino acid utilization.

Abstract

The aim of this study was to estimate lysine (Lys), methionine (Met) and threonine (Thr) requirements for pullets based on protein deposition and efficiency of amino acid dietary, based on the Goettingen University approach. Three assays of nitrogen balance were conducted with White Dekalb pullets, in periods I (14 to 28 days), II (56 to 70 days) and III (96 to 112 days). In each experiment, 56 pullets were distributed in a completely randomized design, with five treatments and six replications. The treatments were five diets with different nitrogen levels keeping constant the ideal ratio (amino acid/Lys), except for the amino acid being tested. Each trial included a control treatment in which a small amount of the amino acid under investigation was added to a diet with the same composition as the diet with the lowest content of the test amino acid to verify that the amino acid under test was first limiting in each trial. The data for nitrogen intake (NI) and nitrogen excretion (NEX) were collected and fitted by an exponential equation for each period to determine the nitrogen maintenance requirement (NMR). The maximum theoretical potential for nitrogen retention (NR_maxT) was determined by the exponential relation between NI and nitrogen deposited (ND) for each period. Based on diets limiting in Lys, Met and Thr, the efficiency (bc^-1) was obtained. The quality of dietary protein (b) is dependent on concentration of the limiting amino acid in the protein of the diet (c). Intake limiting amino acid (LAAI) was calculated. All fitted equations were significant (P<0.01). The NMR values determined were 270 mg/kg^0.67/day, 303 mg/kg^0.67/day and 348 mg/kg^0.67/day, and the NR_maxT values were 3208 mg/kg^0.67/day, 2353 mg/kg^0.67/day and 1739 mg/kg^0.67/day for each period. The bc^-1 values were: 50, 90 and 100 for Lys; 170, 230 and 350 for Met; and 100, 160 and 180 for Thr, for periods I, II and III, respectively. These parameters were used in the formula and LAAI was determined considering 40%, 50% and 60% of NR_maxT for the periods I, II and III, respectively. In general, based on 50% of the NR_maxT values the requirements are lower than recommended in the literature, which is due to the methodology applied in this study (factorial model, type of approach), although the requirements are consistent for pullets.