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Diets providing three levels of protein (14, 18.5 and 23%) and six levels of lysine (3.43, 3.93, 4.43,4.93, 5.43 and 5.93% of C.P.) were fed to triplicate groups of eight male crossbred chicks for the period 14 to 28 days posthatching. The basal 23% protein ration contained protein from sesame meal and gelatin and was supplemented with quantities of essential amino acids equal to the difference between the level supplied by the dietary protein and that recommended by N.R.C. (1971). Amino acid pattern of the 14 and 18.5% protein diets was similar to that of the 23% protein diet since proteinaceous ingredients and crystalline amino acids were reduced in direct proportion to the reduction in protein level. The lysine requirement for maximal weight gain was estimated to be 4.73,4.72 and 4.60% of the protein at 14, 18.5 and 23% dietary protein, respectively. Expressed as a percent of the diet the requirement values were estimated at 0.66, 0.88 and 1.05% at 14, 18.5 and 23% dietary protein, respectively. The results confirm earlier observations that the requirement for an essential amino acid remains essentially constant as dietary protein level is varied between deficiency and adequacy.

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Several 6-day growth assays were conducted to delineate the amino acid limitations of gelatin for chick growth. At a dietary level of 14.5% crude protein, gelatin was observed to be severely deficient in nine essential amino acids. Tryptophan, sulfur amino acids and isoleucine were first, second and third limiting, respectively. Aromatic amino acids, threonine and valine were found to be equally fourth limiting, while leucine, histidine and lysine were seventh, eighth and ninth limiting, respectively. Arginine, glycine-serine and proline were observed to be adequate to super-adequate. Rate and efficiency of gain by chicks fed the completely-supplemented diet were such as to suggest rather high availabilities of amino acids in the protein of gelatin.