Efficiency and incorporation of methionine and cystine in broilers in dose response and marked stable isotope assays

The aim of this study is to determine the relationship between methionine and cystine to optimize the performance of broiler chickens using dose response and stable isotope assays. For the dose-response assay, 600 males, Cobb 500®, 14-28 days old, meeting the requirement for sulphurised amino acids for age (0.851% met+cys), digestible Of 60:40; 54:46; 48:52; 43:57; 37:63, will be obtained by adding synthetic amino acids (DL-methionine and L-cystine) to the basal diet, in the proportions: 100: 0; 75:25; 50:50; 25:75 and 0: 100. The performance (consumption, weight gain and feed conversion) will be evaluated and the amino acid composition of the plucked body and feathers will be obtained by comparative slaughter technique. The efficiency of utilisation will be obtained by sloping the line between consumption and deposition of the amino acid and related to the values obtained in the isotope test for validation of the method. The optimal ratio of methionine to cystine will be determined by a regression analysis between the response and consumption of amino acids. For the stable isotope technique, 60 males, Cobb 500®, will be used. The feed enriched with L-(15N) methionine and L- (15N) cystine will be administered as a function of the body weight of the bird. There will be 3 treatments in reference to the dose response with the ratios of digestible met: cis: 60:40; 48:52; 37:63, obtained by adding synthetic amino acids (Lmethionine and L-cystine) to the basal diet, in the proportions: 100: 0; 50:50 and 0: 100. Feathers, plucked and excreted bodies will be collected, analyzed by na isotope ratio mass spectrometer (IRMS) to quantify isotopic enrichment of tissues. This study aims to promote a better understanding of the metabolism of methionine and cystine and contribute to the traditional methods of quantification of the requirements and the ideal relationship between these amino acids in the diet of broilers. (AU)