Measurement of the nutrient and energy contents of feedstuffs: is the adoption of the latest approaches to analysis overdue?

Context In the past century, many systems have been proposed to represent the energy that animals can derive from their feeds. Productive energy, metabolizable energy (adjusted to nitrogen balance), net energy and net energy based on metabolizable energy systems all have significant drawbacks. This should not be surprising because the various methods have been based primarily on the proximate analysis system developed in the 19th century before the true nature of dietary compounds such as protein and carbohydrates were understood. Aims The Armidale method of describing feed ingredients was proposed because it adresses categories representing 21st century understanding based on analytical chemical techniques for sugars, oligosaccharides, starch, pectin, hemi-cellulose, cellulose, lignin, ash, neutral lipids, polar lipids, true protein and non-protein nitrogenous compounds. Methods The idea of defining ingredient energy in terms of the ATP-generating capacities of the various nutrients has been developed for humans and animals as a refined method of comparing the potential contributions of feedstuffs. Key results The proposed NEATP system facilitates the inclusion of the energy content for each nutrient in each ingredient. All nitrogen-containing chemicals do not have the same energy content, neither do all carbohydrates, etc. NEATP represents the potential energy that animals can get from their feeds. Interactions among nutrients, (e.g. manifestations of the extra-caloric effect of fats) and the nitrogen balance of the animal being fed are properties of the animal and should not be ascribed to the feed. They should be integrated into the formulation models rather than be complicating factors in animal energy bioassays. Conclusions Ascribing traditional metabolizable and net energy assay results to ingredients will always be problematic because heat increment effects are temperature dependent, being helpful to a cool animal, stressful to a warm animal. Implications NEATP based on modern, refined, ingredient composition will contribute to improved profitability and sustainability models of feed formulation for each set of environmental conditions.