ABSTRACT The objective with this study was to determine the lysine maintenance requirements (LMR) of male and female broilers as animal models. A total of 252 birds were used for nitrogen balance trials during three periods (I: 6-21, II: 22-37, and III: 38-53 days). Six lysine levels were used (2.76, 5.88, 8.99, 12.1, 15.2, and 18.3 g kg−1) with six replications. A control group also included, totalizing seven treatments for males and females for each assay. The experimental period was 15 days. The response variables included nitrogen intake (NI) and excretion (NEX), and their difference was assumed to be deposited as nitrogen. An exponential regression between NEX and lysine intake (LI) was fitted, and LMR was estimated when LI = 0. The daily values for LMR were 9.29, 33.4, and 40.2 mg BW0.67 kg−1 for males and 9.36, 30.0, and 39.4 mg BW0.67 kg−1 for females. The final value for both sexes were 10.1 (period I), 31.5 (period II), and 39.8 mg BW0.67 kg−1 (period III). Expressed as body protein weight at maturity (BPm), the LMR were 172 and 148 (period I), 216 and 207 (period II), and 189 and 180 mg BPm0.73 kg−1 (period III) for males and females, respectively. The results provided ranges of LMR values recommended in previous studies, validating this procedure. The procedure to estimate the requirements presented here provides new insights into the model of amino acid requirement estimations.

RESUMO O intuito desta pesquisa foi analisar o ajuste da função Gompertz fixando, ou não alguns parâmetros para descrever o crescimento corporal e dos principais constituintes químicos corporais de frangas de postura em crescimento. Foram coletados semanalmente os dados de peso corporal e os componentes químicos da carcaça depenada e penas de 1.200 pintainhas de quatro linhagens de postura: Hisex marrom, Hisex branca, Hy Line marrom e Hy Line branca W36, até a 18ª semana de idade. As variáveis foram submetidas a dois ajustes, fixando-se ou não alguns parâmetros da função Gompertz. Foram calculados os parâmetros de um modelo alométrico para os componentes químicos. Lipídeo e proteína foram os componentes da carcaça depenada com maior variação nas últimas semanas. Por outro lado, a composição química da pena apresentou pouca variação. Os parâmetros da função Gompertz assumiram valores de acordo com o ajuste empregado, sobretudo para proteína e gordura da carcaça depenada. O ajuste da função Gompertz, fixando os dois parâmetros, permitiu coerência e significado biológico. Os coeficientes alométricos indicaram que à medida que aumentou o peso proteico, aumentou a proporção de gordura e reduziu a proporção de água e cinzas no corpo. O ajuste do modelo, fixando os parâmetros, possibilita coerência com significado biológico, sem perder a precisão nas estimativas.

ABSTRACT The purpose of this research was analyze the fit of Gompertz function with or without fixing some of the parameters to describe body growth and major bodily chemical constituents of growing pullets. Weekly, data of body weight and chemical components of body free of feathers and feathers were collected from 1,200 chicks of four laying strains (Hisex Brown, Hisex White, Hy Line Brown and Hy Line White W36) until 18 weeks of age. The variables were subjected to two adjustments fixing, or not, some parameters of Gompertz function. The allometric model parameters were calculated for the chemical components. The lipid and protein composition of the body free of feathers were the components with the biggest change in the last weeks. Moreover, the chemical composition of the feather showed small variation. The parameters of the Gompertz function assumed values according to the employed adjustment, especially for protein and fat of the body free of feathers carcass. The adjustment of the Gompertz function by fixing the two parameters allowed coherence and biological significance. The allometric coefficients indicate that as the protein weight increased, the proportion of fat increased and the proportion of water and ashes in the body decreased. The fit of the model allows setting the parameters with consistency and biological significance without losing accuracy in the estimates.

The objective of this study was to measure the response of Dekalb White laying hens to different intakes of digestible methionine + cystine (met+cys) to optimise their performance. Two hundred eighty-eight Dekalb White laying hens, ranging in age from 33 to 48 weeks, were used in the study. The birds were randomly allocated into eight treatment (levels of met+cys and the control treatment) groups with six replicates of six hens per unit. The experimental diets consisted of seven increasing levels of met+cys (1.37, 2.75, 4.14, 5.51, 6.89, 7.92 and 8.95 g kg−1) and were prepared using a dilution technique. A control treatment was used to confirm that the limiting response was due to met+cys intake. Egg production, feed intake, egg weight, egg mass and feed conversion per mass were measured. The data were analysed with repeated measures and regression analyses using Broken Line and Quadratic models, as well as using the combination of both models. The different met+cys intakes influenced the studied variables; all the variables except feed conversion per mass were significantly different between the periods and levels. The digestible met+cys intakes based on the association of the Broken Line and Quadratic models to optimise the birds' response to egg mass are 671 mg/bird d for 33 to 36 weeks, 728 mg/bird d for 37 to 40 weeks, 743 mg/bird d for 41 to 44 weeks, and 770 mg/bird d for 45 to 48 weeks.

O objetivo deste estudo foi desenvolver um procedimento baseado na função Gompertz para determinar a eficiência de utilização do aminoácido. O procedimento foi aplicado para determinar a eficiência de utilização da lisina, metionina+cistina e treonina da dieta de frangas de postura em crescimento, e com base nas eficiências foram estimadas as exigências para fase de crescimento das aves. A função Gompertz foi ajustada aos dados de consumo de ração, peso corporal, peso proteico do corpo depenado e peso de penas de quatro linhagens de aves de postura na fase de crescimento. As taxas de consumo e deposição diária de proteína (DP) foram calculadas. A deposição do aminoácido foi obtida multiplicando a DP pela concentração do aminoácido nas penas e corpo depenado. Os resultados obtidos demonstraram que as eficiências de utilização dos aminoácidos diminuíram com a maturidade e, inversamente, houve um aumento proporcional da exigência por kg de ganho de peso. O procedimento baseado na função Gompertz para determinar a eficiência de utilização do aminoácido mostrou ser adequado para avaliar a eficiência de utilização do aminoácido e pode ser uma ferramenta útil para diagnosticar a eficácia do manejo nutricional auxiliando na tomada de decisões sobre o manejo nutricional.

The aim of this study was to develop a procedure based on Gompertz function to determine the efficiency of utilization of amino acid. The procedure was applied to determine the efficiency of utilization of dietary lysine, methionine+cystine and threonine by growing pullets and based on the efficiencies were estimated the requirements for the growth phase of birds. The Gompertz function was fitted to the data of feed intake, body weight, feather-free body protein weight and feather protein weight of four strains of laying hens in the growth phase. The rates of consumption and daily protein deposition (PD) were calculated. The amino acid deposition was obtained by multiplying the PD by the amino acid concentration in feather protein and feather-free body protein. The results showed that the efficiency of utilization of amino acid decreased with maturity and, conversely, there was a proportional increase of the requirement per kg of weight gain. The procedure based on the Gompertz function to determine the efficiency of utilization of amino acid proved to be suitable to evaluate the efficiency of utilization of amino acid and can be a useful tool to diagnose the effectiveness of the nutritional management, aiding in decision-making on the nutritional management.

Broiler strains available in the poultry industry present different requirements for dietary lysine due to their different growth potentials as a result of their genetic makeup. This study aimed to determine the model parameters for maximum nitrogen retention (NRmaxT), the nitrogen maintenance requirement (NMR) and the efficiency of lysine utilization (bc-1) to reevaluate the lysine (Lys) requirements of male and female broilers. Nitrogen balance trials were performed during three periods (I: 6-21 days, II: 22-37 days, and III: 38-53 days). Seven treatments were used for males and females; the treatments consisted of seven diets with protein levels ranging from 61 to 364 g kg-1 dry matter, with Lys being limiting in the dietary nitrogen (4.91 g of Lys in 16 g of N). Nitrogen intake (NI), excretion (NEX), deposition (ND, ND=NI-NEX) and retention (NR, NR=ND+NMR) values were obtained. The NMR was represented by the exponential relationship between NEX and NI. The NRmax T and bc-1 were estimated by the exponential fit between ND and NI. The NRmax T, bc-1, and NMR values were combined in a model to estimate Lys intake by simulating different percentages of the NRmaxT. The Lys intake estimates were 581, 1,538, and 2,171 mg day-1 for males and 512, 1,340, and 1674 mg day-1 for females during periods I, II, and III, respectively. Due to the flexibility of the model, it is possible to calculate the Lys intake for percentages of NR in the range of practical performance data.

Objetivou-se descrever o máximo potencial de deposição de nitrogênio e estimar a ingestão de metionina+cistina pela técnica do balanço de nitrogênio e abate comparativo. Foram realizados ensaios no período de 14 a 28, 56 a 70 e 98 a 112 dias de idade, utilizando 168 frangas Dekalb White, distribuídas em sete tratamentos e oito repetições. Os tratamentos consistiram de níveis de proteína na dieta, variando de 75 a 435 g kg-1 de matéria seca, em que a metionina+cistina foi o primeiro aminoácido limitante. As variáveis coletadas pelo abate comparativo foram nitrogênio ingerido e depositado e, nos ensaios de balanço de nitrogênio, coletaram-se ingestão e excreção de nitrogênio. Por meio da relação exponencial entre ingestão e deposição de nitrogênio, determinou-se a máxima deposição de nitrogênio. As técnicas foram comparadas pelo teste da razão de máxima verossimilhança. As técnicas descrevem de forma diferente o máximo potencial de deposição pela ave, mas são similares na estimativa da exigência de metionina+cistina. Com base em 60% do máximo potencial, as ingestões de metionina+cistina digestível foram estimadas em 163, 243 e 343 mg dia-1 para os período de 14 a 28, 56 a 70 e 98 a 112 dias de idade, respectivamente.

This study aimed to describe the maximum potential of nitrogen deposition and to estimate the intake of methionine+cystine by nitrogen balance and comparative slaughter. Assays were performed in the periodsof 14 to 28, 56 to 70 and 98 to 112 days of age, using 168 Dekalb White pullets, distributed in seven treatments and eight replications. Treatments consisted of protein levels in the diets ranging from 75 to 435 g kg-1 dry matter in which methionine+cystine was the first limiting amino acid. The variables collected by comparative slaughter were nitrogen intake and deposition and, in nitrogen balance trials were collected nitrogen intake and excretion. With the exponential relationship between nitrogen intake and deposition was determined the maximum nitrogen deposition. The techniques were compared by the test of maximum likelihood ratio. The techniques described differently the maximum potential for deposition by the bird, but were similar in the estimation of methionine+cystine. Based on 60% of the maximum potential the intakes of digestible methionine+cystine were estimated at 163, 243 and 343mg day-1 for the period of 14 to 28, 56 to70 and 98 to 112 days of age, respectively.