Effect of Adding Varying Levels of Lysine or Delactosed Demineralized Whey to Wheat Flour on Growth and Body Composition of Young Rats

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Abstract
To a basal diet containing 85% white wheat flour and 4% lactalbumin which furnished 0.49% lysine, increments of 160 mg of lysine were added so that total lysine ranged from 0.49 to 1.29%, but quantities of all other amino acids were constant. The diets were isonitrogenous at 2.22% nitrogen. Weight gains of weanling rats in 28 days were affected significantly (P < 0.01) by added lysine (r = 0.77). The regression of weight gain in grams (Y) on lysine intake in milligrams (X) was Ŷ = 1.91290 + 0.04076X - 0.00010X2. Growth response to daily lysine intakes between 72 and 165 mg of lysine was linear and maximal gain resulted from 165 mg of lysine consumed from the diet containing 0.97% lysine. In a second experiment, dried whey treated by electrodialysis or reverse osmosis was added to white wheat flour but neither lysine nor lactalbumin was included. Ten experimental diets containing 69% white wheat flour and 4, 8, 12, 16 and 20% whey from each source were fed ad libitum to weanling rats for 28 days. Nitrogen content of the diets ranged from 1.53 to 3.36%, and quantities of all essential amino acids were increased simultaneously. Weight gains were influenced significantly (P < 0.01) by level and source of whey and were correlated highly with lysine consumed (r = 0.87). Regression of weight gain (Y) on lysine consumed (X) was Ŷ = -0.73760 + 0.09461X - 0.00029X3. Deposition of nitrogen in liver and carcass paralleled weight gain as in experiment 1. Maximal gains were induced by 101 mg of lysine per day from one diet containing 0.69% lysine and 129 mg from another containing 0.90% lysine. The growth-promoting effects of the two sources of whey did not differ significantly when similar amounts of nitrogen were consumed, but a smaller weight of the whey treated by reverse osmosis than by electrodialysis was needed because of its higher nitrogen content.