Hill and Anderson (1958) and have shown that metabolizable energy of a diet is more precisely measured than is productive energy. In an effort to obtain reliable estimates of useful energy content of poultry feeds, a series of studies have been directed toward determining the metabolizable energy of feed ingredients.

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T HE phosphorus requirement of the laying hen has been studied by many research workers during" the last thirty years. Results reported during the period 1933 to 1953 appeared to indicate a higher requirement than suggested by several more recent reports, and these apparently divergent findings have stimulated additional research at a number of experiment stations. Because of the divergent results, it appeared desirable to review details of both experimental procedures and diet composition in recent and older studies for possible sources of the discrepancies. Among these details have been rate of egg production, length of experimental period, sources of phosphorus, effect of vitamin D level, calcium level, calcium:phosphorus ratios, total feed intake (net phosphorus intake), digestibility of the diet, whether the birds were housed on litter or wire floors, and adequacy of bird numbers and replication such that the results reported were reliable. Although several of these factors have been carefully considered by most workers, concurrent failure to consider others may have permitted conclusions which are of limited value.During egg production, the hen's need

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