Available energy in meat and bone meal as measured by different methods

Estimates of the N-corrected metabolizable energy (MEn) of meat and bone meal (MBM) were made using different methods of bioassay and different levels of dietary substitution. In general, significantly higher MEn values were obtained with 20% than with 40% substitution. Experiments were conducted in an attempt to determine the reason for the lower MEn values at higher dietary MBM levels. The MEn of a simulated MBM consisting of isolated soybean protein, tallow, and minerals with a proximate analysis similar to that of MBM was not lowered by increasing the level of substitution. The MEn of hexane-extracted MBM still was significantly lower at 40% than at 20% substitution. Synergism between types of fatty acids appears to play an insignificant role in the energy differences. In nitrogen metabolism studies, no evidence was obtained that reduced protein digestibility accounted for the lowered MEn values at higher levels of MBM. The average MEn value of MBM determined by the dietary substitution method at 40% was 2.029 kcal/g on an "as is" basis [similar to that of the table value of the National Research Council (1984)]. An MEn value between 2.3 and 2.5 kcal/g appears more appropriate when MBM is used at practical levels in balanced poultry diets.