Improvement of body weight and nitrogen balance of chicks fed histidine-free or lysine-free diets with supplementation of graded levels of sulfur-containing amino acids.

To demonstrate the nutritional specificity of essential amino acids, body weight change and nitrogen balance were compared in chicks equalized-fed a histidine-free or lysine-free diet with 0, 20, 40, 60, 80, or 100% requirement of sulfur-containing amino acids (SAA). With an increase of SAA level up to 40% of its requirement, body weight and nitrogen balance increased irrespective of complete deficiency of histidine or lysine. Above 40% of the SAA requirement, these parameters reached plateaus. The intersection points of the two regression lines at which the responses of body weight change and nitrogen balance altered were 49.8 and 52.1% in the chicks fed the histidine-free diet and 44.7 and 32.6% in the chicks fed the lysine-free diet, respectively. These values are quite agreeable with the estimate of the nutritional score of the amino acid mixtures in an earlier report (Kino and Okumura, 1986). It was demonstrated that the effect of essential amino acid deficiency does not always directly associate with the percentage deficit relative to its requirement, and there exists nutritional specificity of essential amino acids.