Exigência de metionina + cistina digestíveis para frangos de corte de menor potencial genético

Abstract

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.