This statement is a comprehensive presentation of the scientific arguments and aspects relevant to practical feeding and formulation of rations and compound feeds which are important in evaluating feeds for pigs on the basis of metabolisable energy (ME) and net energy (NE).
The ME indicates the capacity of a feed to provide energy for the animal’s metabolism. The NE additionally includes the nutrient-specific heat losses occurring in the metabolism and represents the retained energy (RE) in the growing animal. However, because the extent of these losses is not constant, especially for protein, and the energy requirements for basal metabolism, gestation, thermoregulation and physical activity must be expressed as equivalents to RE, this leads to problems or inaccuracies. The RE as part of performance prediction is therefore only partly successful with a NE system. Only by knowing the composition of the ration, especially its protein and amino acid contents, and the animal’s characteristics, notably protein deposition capacity, is it possible to predict growth, body composition and nutrient excretion.
Extensive calculations carried out in cooperation with a large feed manufacturer have shown that optimisation of compound feeds based on NE versus ME does not lead to a reduction in cost or to a decrease in protein concentration of the feed. Any specific NE system also has the disadvantage of incompatibility with other NE systems, whereas the NE values of different NE systems can generally be calculated from the ME value. A major problem of using NE values is that they cannot be verified experimentally due to the great effort associated with respiration studies. In contrast, ME values can be determined using digestibility studies complemented by urine collection. New findings on nutrient utilisation efficiency and energy requirements can be inserted into recommendations for energy supply more easily and more quickly in a ME system than in NE systems, because in the latter the feed values and hence the feed tables would need to be amended.
It is therefore not advisable, either from a scientific point of view or in the interests of agricultural practice, to convert from ME to one of the existing NE systems. According to current knowledge, ration formulation based on ME is to be regarded as best practice.