Energy evaluation systems for pig diets: a review

Different energy values are given to a given feed according, firstly, to the considered step of energy utilization by the pig (digestible (DE), metabolizable (ME) or net (NE) energy) and, secondly, to the prediction method used for each step. The aspects developed in the first part of this review relate to the effects of chemical composition of the diet and animal factors such as physiological stage or body weight, and also the interactions between diet and animal, on digestive and metabolic utilization of energy. In a second part, the available DE, ME and NE systems when applied to diets or ingredients are presented. In the third part, the different energy systems (firstly DE vs. ME vs. NE, and secondly the NE systems) are compared in terms of advantages, limits and applicability for each of them. The comparison indicates that the hierarchy between diets and, more clearly, between ingredients is markedly dependent on the energy system. The composition of diets (ingredients and chemical characteristics) resulting from least-cost formulation is also affected by the energy system. The last part of the review considers the validity of the different energy systems or their ability to predict pig performance. From this review, it is clear that more emphasis should be given to, firstly, study digestive interactions and, secondly, improve the methods (chemical, physical, in vitro, …) used for (rapid) prediction of energy values of pig feeds.