Energy Evaluation of Feeds for Pigs: Consequences on Diet Formulation and Environment Protection1

The cost of feed is the most important cost in pig meat production (about 60%), and the energy component represents the greatest proportion. Therefore, it is important to estimate precisely the energy value of feeds, either for least-cost formulation purposes or for adapting feed supply to energy requirements of animals. Evaluation of energy content of pig feeds is usually based on their digestible (DE) or metabolizable (ME) energy contents. However, the closest estimate of the "true" energy value of a feed should be its net energy (NE) content which takes into account differences in metabolic utilization of ME between nutrients. In addition, NE is the only system in which energy requirements and diet energy values are expressed on a same basis which should theoretically be independent of the feed characteristics. At each step of energy utilization (DE, ME or NE), different prediction methods can be used. An energy system corresponds then to the combination of one step of energy utilization and one prediction method. The objectives of this review paper are 1/ to consider the main factors of variation of digestive and metabolic utilization of energy in pig feeds, 2/ to present the available energy systems for pig feeds with emphasis given to NE systems, 3/ to compare the energy systems and 4/ to evaluate their ability for predicting pigs performance. Methodological aspects of energy evaluation of pig feeds and complementary information have been considered in previous reviews (Noblet and van Milgen, 2004).