Explain about the Net Protein Ratio (NPR)?

This method was introduced by Bender and Doell (1957) and is a modification of the PER method. In this method, an allowance is made for the protein requirements for maintenance. The method consists of feeding a group of weanling rats on a diet containing 10 percent of the test protein and another comparable control group on a non-protein diet for a period of 10 days. The NPR is calculated by adding the loss in weight of the control group to the gain in weight of the test group and dividing the total weight (g) by the quantity of protein consumed by the test group according to the following formula:

NPR= Gain in weight (g) of the test group + loss in weight (g) of the non-protein group / Protein intake (g)

NPR values have been reported to correlate closely with NPU values.