The nutritional value of poor proteins fed at high levels

Abstract

1. Groundnut flour plus lysine, fed to young rats at a high level as their sole source of protein supported weight gain and nitrogen retention equal to that on what has been considered the ‘ideal’ egg protein diet. For every 100 metabolizable kcal of the groundnut diet that were consumed, 41 came from the dietary protein and there was a net retention of protein equivalent to 14·5 kcal.2. The predicted retention of protein according to the equations of Miller & Payne (1961) for this methionine-deficient protein source, given a score of 56 by FAO (1957), would have been equivalent to only 6·1 kcal and, whatever the level of such a protein in a diet, the maximum predicted retention would be equivalent to no more than 8·5 kcal, or 60% of the best expected with egg as the protein source.3. Feeding a lysine-deficient protein source, wheat gluten, at high levels also gave a greater N retention than had previously been predicted.4. It is concluded that the Miller & Payne (1961, 1963) equations can greatly under-estimate the performance to be obtained from feeding poor proteins at high levels. A revised equation (P. R. Pane, Private communication) predicts much higher results under these conditions.