A Comparison of Biological Methods with Rats for Determining the Nutritive Value of Proteins.

The old-established growth method of Osborne, Mendel & Ferry (1919) for determining the protein efficiency ratio (PER) of protein sources has recently been suggested both in Canada (Chapman, Castillo & Campbell, 1959) and the USA (Derse, 1960) as a routine method for assessing the nutritive value of proteins. Njaa (1963) in a detailed study of the nitrogen balance sheet method for measurement of biological value (BV) (Mitchell, 1923-4a) considers that it and the growth method (PER) are preferable to other biological methods of protein assessment and that the former is more satisfactory than the latter in short-term experiments as it gives both more detailed information and more consistent results. Bigwood (1964) has also recommended BV as the most satisfactory estimate of protein quality. We have already reported (Henry & Toothill, 1962) a good correlation between the N balance sheet and the body-water (Miller & Bender, 1955) methods in assessing the nutritive value of a series of thirty-five protein sources. Sufficient quantities of twenty-four of them were available for the determination of their PER and the results are now reported for values obtained at an 8% level of protein intake. Several methods of protein assessment are compared and the definitions of the terms used are: Retained N x I O O Absorbed N (Mitchell, I 923-4 a) ; Biological value (Bv) =