Determination of the Biological Availability of Methionine and Cystine

Abstract

THERE is no adequate method to determine the biological availability of the sulphur-containing amino-acids in the chick, but Schweigert and Guthneck¹ have described a technique for the rat A method has therefore been developed for the bioassay of methionine using White Leghorn chicks at 11–18 days of age: it can readily be modified to determine methionine plus cystine in terms of methionine equivalence. By difference an indication can be obtained of available cystine. The basal ration contains (per cent) 48.6 maize starch, 35 extracted soybean meal, 5 dried whey, 5 beef tallow, 6 mineral and vitamin mixture², 0.2 choline chloride and 0.2 glycine. All supplements to this ration replace part of the maize starch. Where test materials are calculated to contribute less ‘metabolizable’ energy than starch additional tallow is included to correct for the difference.