Advances in the Assessment of the Nutritive Value of Forages.

Green plants are the major converters of carbon dioxide and water, mediated by sunlight, to produce carbon compounds which sustain animal life. Those primary producers, which consequently constitute a major portion of the herbivore’s diet, are termed forages and take the form of either pasture or harvested feed. The conversion of consumed forage results in ‘value added’ animal products in the form of meat, milk and fiber, and in some cases aspects of recreation. The extent to which a forage source might support the value added product of interest has surely been an emerging question since the domestication of herbivores in systems for human use. By the mid 1800’s, sufficient concern had developed to assess and group nutrients contained in forages in order to provide insight into how a particular forage might contribute to an anticipated animal response. It is the characteristics (chemical, physical, anatomical, etc.) of the forage that determines its nutritive value. Further, it is the subsequent consumption and conversion of those nutrients by the animal that assesses their quality, or in general, provides an estimate of forage quality. The first system that emerged that began to characterize the nature of plant tissue into nutrient entities, conferring nutritive value, was the Weende proximate analyses. This system, consisting of dry matter, crude protein, crude fiber, ether extract, nitrogen free extract and ash, has formed the basis of an evolving process which more precisely characterizes plant fractions that have specific nutritive value and contribute to the estimation or prediction of animal responses. This presentation provides an assessment of the advances made in nutritive value of forages with a transition via in-vitro methods for subsequent forage quality implications in the arena of the ruminant animal.