Evaluation of the Cystine Requirement of the Commercial Laying Hen

Abstract

Five experiments were conducted to determine the contribution of cystine, abbreviated “Cys” to the SAA requirement of the commercial laying hen. En Experiment 1, a corn-soybean meal diet that included casein and gelatin (0.29% Met and 0.16% Cys) was developed for studying the role of Cys in the diet of the commercial laying hen. In Experiment 2, hens responded to Cys supplementation of this diet and in Experiment 3, they responded to supplemental Met. Cystine seemed to be a limiting factor with approximately 3.45 mg Cys required for 1g of egg content (EC). In Experiment 4, a linear response resulted from supplemental Met when Cys was supplemented to furnish in excess of 4.13 mg of Cys/g of EC. In Experiment 5, increasing supplemental Met from 0.28 to 0.32% when the diet contained 0.16% Cys produced a linear response. However, increasing the Cys content from 0.16% Cys produced a linear response. However, increasing the Cys content from 0.16 to 0.18% when the diet contained 0.30% Met resulted in a greater response than from increasing the Met level to 0.32%. It appears that the commercial layer has a Cys requirement of about 3.50 mg/g EC or about 175 mg/day. Therefore, the diet furnished sufficient Cys and it is not necessary to formulate to a requirement for SAA.