Effect of Dietary Energy Concentration on Sulfur Amino Acid Requirements and Body Composition of Young Chicks

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Abstract
A crystalline amino acid diet (17.4% CP) devoid of sulfur amino acids (SAA) was fed at 2,600, 3,000 and 3,400 kcal ME/kg diet. Energy concentration was varied by 400 kcal increments by adding one part cellulose and one part arenaceous flour (ground sand) at the expense of two parts of cornstarch. This method of energy dilution kept the density of the diet essentially constant. At each level of energy, SAA (58% L-cystine and 42% DL-methionine) were fed at 1.72, 2.41, 3.10, 3.79 and 4.48% of the protein. The minimal level of SAA required for maximal gain, evaluated by the method of least squares, was 3.97, 4.08 and 3.85% of the protein at 2,600, 3,000 and 3,400 kcal ME/kg diet, respectively. Similar values were obtained using maximal gain/feed and protein retention as the criteria of adequacy, thus suggesting that the SAA need remained essentially constant at 4% of the CP at all three energy levels studied. Body protein concentration decreased while body fat concentration increased quadratically (P<0.05) as dietary energy content increased from 2,600 to 3,400 kcal ME/kg diet. SAA supplementation caused a linear (P<0.05) increase in body protein and a linear (P<0.05) decrease in body fat. Energy consumption data iluustrated that the chick ate to meet its energy need, since energy intakes were similar at all dietary energy concentrations. Copyright © 1973. American Society of Animal Science . Copyright 1973 by American Society of Animal Science.