Digestive and metabolic utilization of feed energy in swine: Application to energy evaluation systems

Feeds can be attributed different energy values according to, first, the st ep considered in energy utilization (DE : digestible energy, ME : metabolis able energy and NE : net energy) and, second, the method used for estimatio n at each step. This paper reviews some of the most important dietary (chem ical composition) and animal (body weight) factors which affect digestive a nd metabolic utilization of energy by pigs. Available results show that ene rgy digestibility is negatively affected by dietary fibre (DF) content of t he diet and is increased with pig body weight, the negative effect of DF is reduced in heavier pigs, so that most feeds should be attributed at least two different DE values, one for growing-finishing pigs and other for matur e pigs (reproductive sows). Metabolic utilization of energy is highly relat ed to diet chemical composition with higher efficiencies for ME provided by fat or starch. The hierarchy between feeds is then dependent on the energy system, with a clear preference for Ne systems which are the best predicto rs of the "true" energy value of feeds and of performance of pigs. The avai lable NE systems are also compared. Further improvements of energy systems for pigs are discussed.