Calory and Protein Intake as Related to Growth

Numerous recent papers on calory and protein nutrition of fowls have been concerned with the “Calory-Protein Ratio.” This ratio is the nutritional caloric value of the diet divided by the percentage of protein. There has appeared no consistent relation of this ratio to biological results unless either protein or caloric value of the diet has been relatively constant.

Exp. In an experiment on protein and caloric needs, B. B. Bronze hens on range were provided definite intakes of practical formula feeds and grain per day (Table I). Protein intake was calculated from analyses. Caloric intake was expressed as “Productive Energy Values” of Fraps, revised by Titus(1). Most of the reports referred to have also employed such values. These have been expressed as calories per lb. of feedstuff. Correlation of calory-protein ratio to growth results was found to be negligible. It was observed that the product of the caloric and protein intakes showed a good correlation with body weights (coefficient 0.83).

Discussion. The ratio remains the same whether calculated from composition of diet or from intakes, and is independent of the magnitude of intakes. Hence such anomalous findings appear as a decrease in growth when the ratio is increased, due to decreased total feed or decreased protein intake or both(2,3). Protein is represented in the numerator of the ratio as protein calories and in the denominator as percent protein. This implies that all protein simultaneously is consumed to produce calories, and also is utilized for growth purposes, which, obviously, is impossible. Since the ratio includes all the protein calculated both as calories and as percentages of protein the ratio may be expressed:

The first term is a constant. The variability resides entirely in the ratio of non-protein calories to percentage protein.