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Previous issue date: 2015-12-01 === Two experiments were conducted to determine methionine + cystine requirements. The treatments were determined from the basal diet, which was supplemented with increasing values of 99% DL-methionine as a replacement for corn starch. The following values were studied: 0.531; 0.648; 0.765, 0.882, and 0.999% of digestible methionine + cystine for the growth stage and 0.493, 0.600, 0.707, 0.814, and 0.921% of digestible methionine + cystine for the final stage. The experimental design was completely randomized with five treatments and four replicates of 28 chickens per experimental unit, in a total of 560 chickens in experiment 1 and 24 chickens per experimental unit, in a total of 480 chickens in experiment 2. The responses were studied by means of regression analysis, and the estimates of nutritional requirements were determined, when possible, through the study of the quadratic model. Methionine + cystine requirements were estimated at 0.915% for greater weight gain and 0.990% for better feed conversion in the period from 29 to 56 days of age and at 0.815% for greater weight gain and 0.777% for better feed conversion in the period between 57 and 84 days of age. The results of this experiment showed that there are high nutritional requirements for broilers with lower genetic potential, when expressed as a percentage. This is partly due to lower daily consumption when compared with chickens with higher genetic potential. Given the high economic worth of this product on the market, suitable values can be 0.915% methionine + cystine in the period from 28 to 56 days of age and 0.815% methionine + cystine in the period between 57 and 84 days of age. The ratio methionine + digestible cystine/lysine for maximum performance are 83.49% in the period from 28 to 56 days and 74.36% in the period from 57 to 84 days. === Foram realizados dois experimentos para a determina??o da exig?ncia de metionina + cistina digest?vel, sendo os tratamentos estabelecidos a partir da ra??o basal que foi suplementada com valores crescentes de DL- metionina 99% em substitui??o ao ingrediente amido de milho. Foram estudados os valores de 0,531; 0,648; 0,765; 0,882 e 0,999% de metionina + cistina digest?vel para a fase de crescimento e de 0,493; 0,600; 0,707; 0,814 e 0,921% de metionina + cistina digest?vel para a fase final. Foi utilizado o delineamento inteiramente casualizado, com cinco tratamentos e quatro repeti??es de 28 aves por unidade experimental, totalizando 560 aves no experimento 1 e 24 aves por unidade experimenta, totalizando 480 aves no experimento 2. As respostas foram estudadas por meio de an?lise de regress?o, sendo as estimativas de exig?ncias nutricionais estabelecidas, quando poss?vel, atrav?s do estudo do modelo quadr?tico. As exig?ncias de metionina + cistina digest?vel foram estimadas em 0,915% para maior ganho de peso e 0,990% para melhor convers?o alimentar no per?odo de 29 a 56 dias de idade e em 0,815% para melhor ganho de peso e 0,777% para melhor convers?o alimentar no per?odo de 57 a 84 dias de idade. Os resultados do presente experimento evidenciam que as exig?ncias nutricionais de frangos de corte de menor potencial gen?tico, quando expressas em porcentual, s?o elevadas, em parte devido ao menor consumo di?rio quando comparado aos frangos de maior potencial gen?tico. Devido ? grande valoriza??o econ?mica deste produto no mercado podem ser recomendados os valores de 0,915% de metionina + cistina no per?odo de 28 a 56 dias de idade e de 0,815% de metionina + cistina no per?odo de 57 a 84 dias de idade. As rela??es metionina + cistina/lisina digest?vel para m?ximo desempenho s?o de 83,49% no per?odo de 28 a 56 dias e 74,36% no per?odo de 57 a 84 dias.
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