Energy/protein ratio in natural-ingredient diets for weanling rats. II. Energy and protein retention and efficiency of retention

Abstract

A 3 × 3 factorial experiment was carried out, in which natural ingredient diets formulated at 3 digestible energy levels (DE) (100, 90 and 80% of NRC, 1978 recommendations) and at 3 energy: protein ratios (EPR) (63, 71 and 79 kJ DE/g crude protein (CP)) were fed to 8 weanling male Wistar rats/group. Half of these animals were sacrificed at the end of the 6-week experimental period and their body composition analyzed. Retentions of protein and energy were assessed by difference from a similar group of 8 rats killed and analyzed at the beginning of the experiment. No interaction was found between the 2 factors studied. Main results showed a decrease in intake and retention of both energy and protein, without affecting the efficiency of retention when energy level of diets was reduced by 20%. An increase in the EPR of the diets led to a decrease in protein intake and to an increase in efficiency of protein retention, without affecting the amount retained. No changes in body composition, nor in composition of live weight gains were found as a result of treatments. It is concluded that a 10% reduction in DE level of the diet is of no consequence, and that an EPR of 79 kJ/g leads to more efficient use of the dietary protein without detrimental effects over any other nutritional indicator.