Protein and Energy Utilization by Chicks Fed Graded Levels of a Balanced Mixture of Crystalline Amino Acids

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Abstract
Graded levels of a balanced amino acid mixture from zero to 30.85% of the diet were fed to chicks from day 8 to day 21 posthatching to evaluate performance, body composition and protein (N × 6.25) as well as energy utilization. Body and liver composition changed markedly in response to changes in the dietary calorie/protein ratio. Percentage body fat increased and percentage body protein decreased as the concentration of dietary amino acids was increased from zero to 11.57% of the diet. However, dietary amino acid increments between 11.57% and 30.85% resulted in a precipitous decrease in percentage body fat and an inverse rise in percentage body protein and water. Liver fat reached a maximum at a low level of protein intake, then steadily declined. Throughout a dietary range of zero to 23.14% of the amino acid mixture, body protein retention, weight gain and liver protein increased linearly when evaluated as a function of protein intake. Energy utilization was found to be constant at all levels of metabolizable energy consumed. Our results support the conclusion of Hegsted and Neff that protein utilization is constant throughout a wide range of protein intake up to the point of maximal protein retention and weight gain.

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