Energy requirements and responses: a UK perspective

Abstract

AbstractOngoing improvements in the genetic merit of United Kingdom (UK) dairy cows as well as changes in the national milk market will increase awareness of and provide focus on the importance of balanced nutrition, particularly with respect to energy and protein. Within the UK, energy is rationed according to the metabolizable energy (ME) scheme, proposed in the 1960s and implemented in the late 1970s. Whilst a significant improvement over previous rationing systems, deficiencies in the scheme have been identified. These relate to an inability to predict animal response including the importance of nutritionally induced changes in milk composition, and to represent adequately body tissue mobilization in early lactation and the control of nutrient partitioning during the phase of tissue repletion. Some of these issues are addressed in this paper. These include the problems likely to occur in formulating rations for dairy cows producing in excess of 50 kg milk per day during significant parts of the lactation, which leads to an appraisal of some of the concepts embodied in the current ME system. By reference to appropriate experimentation, the importance of recognizing the nutrient composition of ME as well as the significance of nutrient metabolism in the portal drained viscera and the liver is established. The rôle of added fat within the diet is discussed, whilst the quantitative importance of mobilized body tissue to whole body energy metabolism and the interaction between specific nutrients is recognized. Finally, it is concluded that a complete revision of the ME system is unlikely at this stage and therefore it will be prudent to deploy available resource to modify the existing ME model in line with some of the inconsistencies and weaknesses that have been identified.