Energy/protein ratio in natural ingredient diets for weanling rats

The effect of 3 levels of Digestible Energy (DE; 100, 90 and 80% of NRC Recommendations) and 3 different Energy/Protein ratios (EPR; 63, 71 and 79 kJ DE/g Crude Protein [CP]) were studied in a 3 X 3 factorial design using 8 weanling rats per group and diets formulated with natural ingredients. A 20% reduction in DE level decreased significantly energy and protein intake and daily weight gain, and increased the feed intake/body weight gain ratio without affecting protein or energy conversion ratios. Wider values of EPR brought about a decrease in protein intake and CP/body weight gain ratio, with no effect on feed and energy intakes, conversion ratios, nor weight gain. At the protein levels used, energy but not protein concentration of diet, determined growth rate; with the natural ingredient diets used, up to 10% reduction in DE level may be compensated for; wider EPR values led to more efficient utilization of dietary protein.