T HE need for a rapid assay capable of measuring biologically available energy is well recognized by those concerned with the purchase of feed ingredients, the formulation of poultry diets and the quality control of mixed feeds. Conventional biological assay techniques for metabolizable energy (M.E.) require more time than is normally available when the data are to be used in the above practices. Tables of biologically derived M.E. data, while capable of serving as useful guides to ingredient purchasers and diet formulators, are not entirely satisfactory since M.E. values for samples of an ingredient may be extremely variable. For example, Sibbald and Slinger (1962) reported that M.E. values for 25 samples of wheat ranged from 1,340 to 1,800 Cal. per lb. of dry matter. Carpenter and Clegg (1956) compared the chemical compositions of 13 feed ingredients and 4 mixed diets with classical M.E. values obtained from total collection studies with adult hens. The following equation was found to be capable of predicting the M.E. value of a feedingstuff: M.E. (Cal./Kg.) = (0.59X% dry matter)+ 38B where B = (% crude protein +2.25X% ether extract +1.1X % starch + % sugar) The residual standard deviation associated with the equation was reported to be +190 Cal. per kilogram. Davidson et al.
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