Characterization of useful energy content in swine and poultry feed ingredients

Abstract

For effective use of feed ingredients in diets for the various classes of animals, it is important that the feeding value of feed ingredients is properly estimated. This applies in particular to the useful or bio-available energy content, as feed energy generally represents the single largest cost-factor in animal production. In spite of their limitations, digestible energy (DE) and metabolizable energy (ME) systems are used widely in North America to estimate the useful or bio-available energy content of feeds and feed ingredients for pigs and poultry, largely because experimental procedures to establish DE and ME values are relatively simple. Some of the limitations of DE and ME systems can be overcome by using empirical net energy (NE) systems, whereby feed or feed ingredient NE content is predicted from digestible nutrient contents. However, empirical NE systems require estimates of the animal’s maintenance NE needs, which cannot be measured directly and have been estimated to vary between 489 and 750 kJ kg-1 BW0.60. Moreover, estimated feed or feed ingredient NE contents only apply to one particular animal state. The practical application of NE prediction equations requires an accurate characterization of nutrient contents and digestibility of feeds and feed ingredients. An accurate and flexible assessment of animal and feed effects on energy utilization requires the use of mathematical models in which transformations and use of dietary nutrients for different body functions are represented. Effective use of such nutrient flow models requires accurate characterization of feeds and feed ingredients and of animals in aspects of nutrient partitioning for the various body functions. This type of model can be used to predict accurately the useful energy supply from feeds and feed ingredients for specific animal states for diet formulation purposes. Nutrient utilization models may be refined to explore additional aspects of nutrient utilization, such as dynamics of nutrient absorption, the utilization of nutrients via alternative and competing metabolic pathways and inter-organ nutrient metabolism. Key words: Digestible energy, energetics, feed ingredients, metabolizable energy, net energy, nutrition, pigs, poultry