Metabolic plus endogenous energy and nitrogen losses of adult cockerels: the correction used in the bioassay for true metabolizable energy.

Three experiments were made with adult White Leghorn cockerels to measure the effect of indigestible organic matter on the metabolic fecal and endogenous urinary energy and nitrogen losses. When a cellulose:carboxymethyl cellulose mixture was placed in the crops of fasted birds the energy excreted during the subsequent 24 and 48 hr was greater than, but proportional to, the energy input. The linear regression coefficients were not different (P greater than .05) from unity, indicating that the metabolic and endogenous energy output neither increased nor decreased when cellulose was administered. This finding was confirmed when graded levels of sawdust were fed in place of cellulose. It is concluded that the use of a fasted bird to measure the metabolic and endogenous energy loss, as in the bioassay for true metabolizable energy, is valid and the changes induced by the nature or quantity of dietary fiber are insignificant. Nitrogen excretion was not affected by the feeding of cellulose or sawdust. Excretion increased with the duration of starvation but the difference diminished as the bird aged and became heavier. Nitrogen losses varied greatly among birds but tended to be characteristic of a bird within an experiment.