Comparison of the National Research Council energy system for lactating cows with four European systems.

The structure, prediction steps, and accuracy of the US (NRC), United Kingdom (ARC), Dutch (VEM), French (UFL), and German (NEL) systems for feeding high producing cows were compared. Simulations were made using 15 feeds ranging from hays to cereals. Agreement was satisfactory among European systems for the prediction of metabolizable energy and net energy for lactation (NEL) contents of feeds and the quantities of feeds in balanced diets necessary to meet the energy requirements of lactating cows. The metabolizable energy and NEL contents of feeds seemed overestimated by the US system compared with results using the European systems, and the ratio of NEL to total digestible nutrients was almost constant, unlike the other systems. Estimating the NEL content of feeds for a level three times maintenance intake allowed satisfactory rationing for the production of 20 to 25 kg of fat-corrected milk/d. However, feed allowances seemed underestimated for higher milk production, especially with diets based on hay, probably because of the overestimation of feed NEL content, the underestimation of level of feeding, and the effects associated with feeding levels > 3 and high concentrate diets.