INFLUENCE OF AMINO ACID EXCESS ON ENERGY UTILIZATION IN THE GROWING CHICK

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Abstract
Two semi-purified diets equal in classical metabolizable energy level and first limiting essential amino acid level but differing in crude protein content by 25% were fed to 3-week-old chickens. All birds had been carefully selected and were reared either in individual cages for limit feeding or conventional cages for ad libitum trials. The two diets promoted equal growth when fed ad libitum in pelleted form but not if fed in the form of mash, where the higher protein diet promoted a higher rate of gain. The higher protein diet resulted in superior feed efficiency with both pelleted and mash diets fed ad libitum, and also superior performance when fed either as mash or pellets on a limited basis. Total carcass energy was decreased with the higher protein diet, as was the efficiency of energy retention. The data obtained contradict the accepted theory that the better the balance of dietary nutrients, the better the metabolizable energy utilization. A direct measurement of oxygen consumption supported the hypothesis that difference in metabolizable energy utilization was mainly due to heat increment of the diets.