Determination of the Metabolizable Energy of Organic Nutrients for the Rat

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Abstract
With the purpose of ascertaining the applicability of the Atwater energy conversion factors to rat nutrition, three balanced diets differing widely in their proportions of calorigenic nutrients (casein, starch, and a mixture of fats) were fed to 12 adult rats according to a 3 × 3 latin square design, and the metabolizable energy for each diet for each rat was determined in 34 metabolism periods. The metabolizable energy values were then factorized into values for the three energy-yielding nutrients, using a multiple regression equation of the type: ME = cC + sS + fF, in which ME is the determined metabolizable energy for the diet, C, S and F the weights consumed of casein, starch and fat, respectively, and c, s and f the constants to be determined from the 34 sets of data by the method of least squares, representing the metabolizable energy per gram of the respective nutrients. The metabolizable energy values thus obtained with their standard errors are as follows: Analyses of the urine of rats on a very high-protein diet for energy and total nitrogen yielded 6.29 cal. per gram of urinary nitrogen. This value was used in correcting urinary energy to nitrogen equilibrium.

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