Comparison of Metabolizable Energy and Productive Energy Determinations with Growing Chicks

Abstract

Experiments have been conducted to compare the determination of metabolizable and productive energy of a semipurified reference diet for the growing chick. Metabolizable energy was found to be independent of plane of food intake in the range from 100 to 30% of ad libitum intake. Replicate determinations gave a mean value of 3.34 Cal. per gram of dry matter with standard deviation ± 0.04. In contrast, replicate determinations of productive energy were highly variable, ranging from 2.06 to 3.31 Cal. per gram with a mean of 2.49 ± 0.42. From a regression analysis of all available data, its mean productive energy was 2.58 Cal. per gram. No consistent relationship between plane of food intake and productive energy value was found. The observed productive energy was approximately 20% greater than estimated from the productive energy data of Fraps for the components of the diet. This was considered to be due to the superiority of the diet used in the present work as compared to the earlier studies of Fraps. Productive energy in the present experiments was approximately 77% of metabolizable energy. The large difference between the two measures was not diminished by changes in method of computation involving the relation between body size and maintenance requirement or the energy equivalent of tissue protein. Its possible significance was discussed.