True Metabolizable Energy Corrected to Nitrogen Equilibrium

A study was conducted to examine the effects of the correction of excreta energy to nitrogen equilibrium in the determination of true metabolizable energy (TME). Roosters and laying hens were fed diets consisting of a standard layer ration blended with increasing amounts of dehulled soybean meal ranging from 0 to 100%. Dry matter digestibility, nitrogen retention, and apparent metabolizable energy were greater for females than the males. For males and females, dehulled soybean meal had values for dry matter digestibility of 50.1 and 52.0%, TME of 3.087 and 3.145 kcal/g dry matter, metabolizable energy corrected to nitrogen equilibrium (MEn) of 2.683 and 2.719 kcal/g dry matter, and TME corrected to nitrogen equilibrium (TMEn) of 2.890 and 2.946 kcal/g dry matter, respectively. The differences between TME and TMEn values were due to larger nitrogen losses from nondietary sources by fasted birds than by fed birds. Thus, the metabolic fecal and endogenous urinary energy as measured from the fasted birds provides a larger correction than justified for accurate TME determinations. The difference between the TME and the TMEn in this study explains in part the previously reported abnormally high values for TME over MEn. Thus, MEn appears to be a more accurate measurement of metabolizable energy than TME.