Nutritionists have been discussing whether the dietary supplementation of cyst(e)ine is required as a part of the dietary methionine (Met) in the total sulfur amino acid (TSAA) requirement to achieve optimum performance in broilers. Part of Met is converted to cysteine (Cys) to meet the Cys requirement, especially for feather growth. The TSAA requirement has been determined by using graded levels of free Met in the diet, without supplementation of free cyst(e)ine. It has also been argued that the Met to Cys ratio (Met : Cys) changes with age and even with different Met sources. The objective of this study was to evaluate the two sources of Met, while determining the proportion of Met and Cys in total dietary TSAA that optimize the performance of broilers. A performance assay was carried out in a factorial arrangement (5 × 2) using 1080 broilers from 42 to 56 days of age fed diets having different dietary proportions of Met and Cys (44 : 56, 46 : 54, 48 : 52, 50 : 50 or 52 : 48) while maintaining the same dietary TSAA in the diets. Two synthetic Met sources (dl-Met or l-Met) were used for each of the diets with different dietary Met : Cys ratios. Twenty-one broilers of the same age were fed the diets 44 : 56, 48 : 52 and 52 : 48 by supplementing the diet with L-(15N) Met or L-(15N2) Cystine to study the metabolism of TSAA. No differences were observed between Met sources for feed intake, BW gain and feed conversion ratio (FCR; P > 0.05); however, FCR was numerically improved at 50 : 50 Met : Cys. Regarding TSAA utilization, the conversion of Met to Cys increased with increase in Met : Cys ratios, but the concentration of Met intermediates decreased. Broiler chickens responded to different dietary proportions of sulfur amino acids by altering their sulfur amino acid metabolism, and diets containing 50 : 50 Met : Cys is recommended for broilers of age 42 to 56 days.

营养学家一直在讨论囊肿（E）INE的饮食补充是否需要作为膳食的一部分甲硫氨酸（Met）在总含硫氨基酸（TSAA）要求，以实现在肉鸡最佳性能。Met的一部分会转化为半胱氨酸（Cys），以满足Cys的要求，尤其是对于羽毛的生长。TSAA要求是通过在饮食中使用分级的游离Met水平确定的，而无需补充游离的胱氨酸（e）。也有人认为Met与Cys的比率（Met：Cys）随年龄甚至Met来源的变化而变化。这项研究的目的是评估Met的两种来源，同时确定Met和Cys在总日粮TSAA中的比例，从而优化肉鸡的生产性能。使用因子水平（5×2），使用42至56天龄的1080只肉鸡，以不同的Met和Cys饮食比例（44：56、46：54、48：52、50： 50或52：48），同时在饮食中保持相同的饮食TSAA。两种合成的Met来源（dl -Met或l -Met）用于具有不同饮食Met：Cys比的每种饮食。通过向日粮中补充L-（15 N）Met或L-（15 N 2）胱氨酸研究TSAA的代谢。在Met来源的采食量，体重增加和饲料转化率之间未见差异（FCR；P > 0.05）；但是，FCR的数值在50:50 Met：Cys时有所改善。关于TSAA的利用，Met向Cys的转化随着Met∶Cys比的增加而增加，但是Met中间体的浓度降低。肉鸡通过改变硫氨基酸代谢来应对不同饮食比例的硫氨基酸，对于42至56日龄的肉鸡，建议日粮中含有50:50 Met：Cys的日粮。