The responses of rats to various combinations of energy and protein I. Diets made from purified ingredients

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Abstract
Male and female weanling rats were fed ad libitum for 28 days on purified diets with metabolizable energy levels of 8·0, 9·5, 11·0 or 12·5 MJ/kg and protein:energy ratios of 1:1, 1·33:1, 1·67:1 or 2:1 %:MJ/kg at each energy level. Major nutrients were balanced in proportion to energy and protein. The following parameters were measured: food intake, bodyweight, body length, abdominal fat, liver and kidney weights. Increasing dietary energy level reduced food intake but the reduction was not sufficient to prevent an increase in energy intake. This was reflected by increases in bodyweight, body length, abdominal fat, and relative liver and kidney weights, especially in male rats. Higher energy intake increased weight gain and food conversion efficiency to a greater extent than higher protein intake. The response to protein intake at different energy levels was not consistent. There was no common protein:energy ratio for overall good performance. It is concluded that rat growth and other features can be controlled by the alteration of dietary energy and protein levels.