An historical perspective: the development of methods for assessing nutrient requirements

Interest in the assessment of the nutrient requirements of ruminants arises from the practical need to sustain or manipulate the production of meat, milk or wool. A difficulty in making such an assessment has always been the definition of what constitutes a nutrient (see This is well illustrated by the history of attempts to express the nutritive value of feeds as sources of energy and to relate these to energydemanding processes of both the rumen and the body proper.