FEW new energy sources have proved to be worth exploiting for the feeding of non-ruminants.Cereals and root crops remain the main sources of energy, with fibrous materials, whether in their native or processed state, playing a very small part. However, American feeders have recently begun to use low-grade fats, inedible by man, in poultry feeding.With protein concentrates more attention is being given to improving the methods of processing to obtain materials of higher nutritive value than to developing new products. Since many materials at the onset of processing have a high intrinsic nutritive value, the problem is to devise methods of processing that will minimize loss of this value in the by-product destined for animal feeding. In some cases, as in the production of white iish meal and soya-bean meal, processing requirements are well understood. In other cases little is known, or obstacles stand in the way of adopting superior processing methods.One of the commonest and most informative is the biological value (BV), essentially a measure of the nutritive value of absorbed nitrogen. Another is the gross protein value (GPV), which is a measure of the value of the protein in a concentrate for supplementing the proteins in mixtures of cereals and miller's offals.In Table I1 (p. 243) are set out the GPV ratings of a number of concentrates, most of which * Part I: