Metabolizable energy corrected for total nitrogen (TN) retained or lost from tissues: MnE = ME – (κ x TN). For birds or monogastric animals, gaseous energy loss is usually not considered. The correction for mammals is generally k = 7.45 kcal/g nitrogen retained in the body tissues (TN). The factor of 8.22 kcal/g TN is used for birds representing the energy equivalent of uric acid per gram of nitrogen. A number of different values for k have been suggested and used.