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Lysine and Threonine Supplementation of Rice

Stine Laboratory, E. I. du Pont de Nemours and Co., Inc., Newark, Delaware

Precooked rice diets, supplemented with graded amounts of lysine and threonine, the first two limiting essential amino acids, were fed to over 800 weanling male rats. Fourteen different levels of lysine were tested in various combinations with 7 different levels of threonine. Equations expressing the animal's growth and efficiency of feed utilization were developed and verified by regression analysis using the Univac. According to these calculations best performance occurs when 0.34% of lysine (0.425% L-lysine · HCl) and 0.18% of threonine (0.36% DL-threonine) are added to this rice diet. On the basis of the microbiologically determined lysine and threonine content of the unsupplemented rice diet, the diet supplemented for optimum performance contains 1.4 times as much L-lysine as L-threonine.

When the amount of one amino acid is held constant at a suboptimal level and the other varied, a slightly greater amount of the second is required than expected from the above ratio to give optimal performance. Mass action is a possible explanation of this phenomenon.

The experimental results support the principle that multiple essential amino acid supplementation of a protein should be carried out in such a manner that, according to the needs of the organism, the supplemented amino acids are present in the proper ratio to each other and in balance with the next limiting amino acid or nutrient in the diet.