Abstract
Natural diets with metabolizable energy levels of 8·5, 10·0, 11·5 or 13·0 MJ/kg and protein:energy ratios of 1:1, 1·33:1, 1·67:1 or 2:1 %:MJ/kg were fed ad libitum for 28 days to male and female weanling rats. Records of food intake and bodyweight were maintained weekly, and at post mortem examination body length, abdominal fat, liver and kidney weights were measured. Food intake was reduced when dietary energy level increased but this reduction was not sufficient to prevent energy intake increasing, especially in males. Female rats showed only small increases in energy intakes as dietary energy levels rose. The increase in energy intake at higher dietary energy levels increased food conversion efficiency, weight gain and abdominal fat deposition. The responses of male rats were greater than females. Protein intake had a smaller and less consistent effect than energy intake. Increased protein:energy ratio resulted in higher absolute and relative liver and kidney weights and greater body length. This reflected the increase of bodyweight gain at higher protein:energy ratios.