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The metabolizable energy values of 17 samples of cereals, cereal by-products and mixed rations have been determined with laying hens. They ranged from 1300 to 3500 kg.-cal. per kg. and, where comparison with the findings of other workers has been possible, agreement has been generally satisfactory. The same samples were subjected to the standard methods of proximate analysis, and also analysed for their content of starch and reducing sugars using a specially modified anthrone method. Statistical analysis of the results showed that the formula-53 + 38 (yo crude protein + 2.25 x yo ether extract + 1.1 x yo starch + yo sugar) gave predicted figures for the metabolizable energy (in kg.-cal./kg.) of the materials tested with a standard deviation of & 190 kg.-cal./kg. from the determined figures. This was a superior prediction to any that could be made with the data from proximate analysis alone, and the method may prove of use when an estimate of the energy value of a material or mixture for feeding to poultry has to be made from results of chemical analyses that can be carried out in a routine laboratory. IntroductionIf two mixed rations are both adequately fortified with protein, minerals and vitamins, the principal factor limiting the productive performance that can be obtained with the same quantities of each are their respective energy contents. For the same performance less is required of the ration with higher energy content.It is of obvious value to have simple routine methods of chemical analysis that can be used to estimate the nutrient content of rations and their component parts. For single specific nutrients, such as the individual minerals and vitamins, this is a straightforward analytical problem. The energy ' value of a feeding stuff is not however a function of content of any single chemical entity. The vaIue of any formula used to estimate the energy content of a feeding stuff from its chemical analysis must therefore depend, in an empirical way, on the correlation of such calculated figures with experimentally determined energy values.There is general agreement that the standard system of proximate analysis does not give figures that can be correlated closely with the energy value of poultry feeding stuffs. This is largely explain,ed by the great differences in the digestibility of the ' nitrogen-free extractives ' (N.F.E.) of different materials.'* a However, in one series of digestibility trials, with more detailed analysis of nine materials, it was found that the portion of the N.F.E. analysed as ' starches + polysaccharides + reducing sugars was in each case over 90% digestible, and their content of these carbohydrates ranged from 4 to 63y0.1 The contribution of digestible nutrients

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