Tryptophan Utilization in a Threonine-induced Amino Acid Imbalance in Weanling Rats: Gain in Weight and Carcass Nitrogen with Two Feeding Methods

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Abstract
The effect of a threonine-induced amino acid imbalance on tryptophan utilization in weanling rats was evaluated by determining weight gain and carcass nitrogen. Balanced and imbalanced niacin-free casein diets were either fed ad libitum or fed by a method in which the protein portion of the diet was given separately, twice daily, with the remainder of the diet available ad libitum. The depression in weight gain and food consumption, normally observed with ad libitum feeding of an imbalanced diet, was eliminated with separate feeding of the protein at levels equivalent to 0.4 to 0.8 g casein/day. Thus utilization of the protein did not appear to be impaired by the imbalance when the proteins were fed separately. When the percentage of the imbalanced mixture was increased in the diet of the ad libitum-fed animals, growth and food consumption were lower than those of the casein controls. Incorporation of niacin in the diet eliminated the adverse effects of the imbalance in the ad libitum-fed animals. Although there had been no depression in growth in the animals fed the proteins separately, the addition of niacin caused an increase in both weight gain and carcass nitrogen.