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A total of 56 Hy‐line W‐36 hens from 28 to 30 weeks were used on nitrogen balance (NB) trial to estimate daily N maintenance requirements (NMR) and the genetic potential for daily N retention (NRmaxT). The treatments consisted of six graded levels of nitrogen in the diets (N1 = 8; N2 = 16; N3 = 24; N4 = 32; N5 = 40; and N6 = 48 g N/kg of feed), formulated using the dilution technique. The regression analyses between nitrogen intake and excretion were performed to fit the exponential function and to determine the NMR = 292 mg/BWkg 0.67, which was applied for further calculation of NRmaxT = 1,883 mg/BWkg 0.67. A second NB trial was conducted, and a total of 96 Hy‐line W‐36 hens were used in the same period to estimate the ideal amino acid ratio (IAAR). Twelve treatments with eight replicates and one bird per cage were used. A balanced diet (BD) was formulated to meet the IAAR and the requirement of other nutrients for pullets. The limiting diets were formulated diluting BD with cornstarch and refilled with synthetic AAs and other feed ingredients, except for the AA under study. In each trial, the data of nitrogen intake, excretion, deposition and retention were obtained in a NB trial. The IAAR determined by Goettingen approach was Lys 100, Met+Cys 88, Trp 21, Thr 69, Arg 109, Val 90, Ile 75, Leu 127, Phe+Tir 110, Gly+Ser 73 and His 29%. The IAAR determined by Louvain approach was Lys 100, Met+Cys 88, Trp 21, Thr 69, Arg 104, Val 91, Ile 78, Leu 121, Phe+Tir 119, Gly+Ser 77 and His 29%.

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Context Knowing the broilers’ response to the intake of balanced protein allows nutritionists to choose the optimal level to be used in the feed. Aims The objective of the present study was to describe the response of male and female broilers of two commercial strains to a range of dietary balanced protein levels. Methods In total, 2496 sexed chicks (equal numbers of Ross 308 and Cobb 500) were used. Six dietary balanced protein levels × two strains × two sexes (24 treatments) were randomly allocated to 96-floor pens, using four replications of 26 chicks each. Feed intake, bodyweight, feed conversion efficiency, carcass weight and the weights of the breast without skin, thigh plus drum (leg) and wing were measured at 14, 28, 42 and 56 days of age. Key results Feed intake in all periods in both strains and sexes increased as the dietary balanced protein level decreased, and then decreased markedly at the lowest balanced protein levels. Only at 14 days did the responses differ between strains and sexes; in all other cases, the responses differed only between sexes. At 14 days, the response in bodyweight differed between strains and sexes, whereas at all other samplings they differed only between sexes. The response in carcass, breast and wing yield at 14 days was the same for both strains and sexes but differed between strains and sexes at 28 days. At 42 and 56 days, the response differed only between sexes. The response in leg (thigh-plus-drum) weight at 14 days was the same for both strains and sexes, but after that differed between sexes only. Body lipid content increased linearly initially, and then quadratically, as dietary protein content was reduced. Conclusions Appropriate equations are presented for describing the above responses of broiler chickens, male and female, from two commercial strains. Implications The fitted equations may be used to calculate the optimum economic level of dietary balanced protein to be used under different economic circumstances.

A digestibility assay was conducted in order to determine the digestibility coefficients (DC) of amino acids of feed ingredients in cecectomized adult roosters. In total 48 cecectomized adult roosters were used to assess the coefficient of digestibility of 7 ingredients: corn, soybean meal, soybean concentrate, corn gluten meal, wheat bran, peanut meal, and feather meal. Each ingredient was replicated six times and a group of 6 rooster was used to measure endogenous amino acid losses. After 48 hours of fasting, the roosters were tube fed 20g of ingredients tested twice during a day. At 12 hour-intervals excreta and endogenous losses were collected and immediately freezedried for further chemical analysis. At the end of the assay, excreta were weighed and samples of ingredients, excreta, and endogenous losses were pooled and analysed for dry matter, nitrogen and amino acid content. The coefficients of indispensable amino acids for the most feed ingredients assessed in the current research were similar to published literature like AMINODat ® 5.0 and the 4 th edition of the Brazilian Tables for Poultry and Swine, except feather meal, in which only digestible Trp and Thr content were similar to literature. Particularly, the coefficients for some amino acids like Arg and Gly exhibited large discrepancies from literature in almost all the feed ingredients assessed herein. In general, using cecectomized adult roosters proved to be a reliable technique to assess the digestibility of feed ingredients used in poultry diets.