net energy, swine, feed efficiency


Net energy (NE) is one member of the sequence of energy systems which also includes gross energy (GE), digestible energy (DE), and metabolizable energy (ME). It is perhaps the most sophisticated because it attempts to consider more components of the ingredient or diet which normally cannot be used by the pig for maintenance and/or productive purposes. Gross energy makes no such adjustment and therefore has little direct value in diet formulation. Digestible energy corrects for energy which is lost in the feces, and metabolizable energy also adjusts for energy lost in the urine. The data in Table 1 reveal that heat increment averages 22% of gross energy, and ranges from 17 to 28%, across an array of ingredients that are frequently used in commercial pig diets. Interestingly, the range in NE is about 81%, much greater than the range in ME at 55%. At a very crude level, this suggests that NE accounts for more variation among ingredients than does ME; looked at another way, using ME to formulate diets essentially assumes that HI is similar across ingredients and does not need to be considered. Of course, this is not true.