2.1 The Nitrogenous Constituents of Fresh Forages

Abstract

The nitrogenous composition of forage is largely determined by the requirements of plant physiology, with variables such as anatomy, e.g. monocotyledons v. dicotyledons, maturity, fertilizer treatment, climate, light intensity, etc., superimposed. One would therefore expect to find many broad similarities in the composition of plants. Chibnall (1939) recognized this and gave a comprehensive review of early work on metabolism and nitrogenous composition of leaves. Present systems for the assessment of protein requirements of ruminants (e.g. Agricultural Research Council, 1980) require a detailed knowledge of the composition of feedstuffs in terms of rumen degradable and undegradable proteins and of non-protein nitrogenous compounds utilized by rumen microorganisms. It is also apparent that the biological value of protein which bypasses the rumen should be determined. Descriptions in terms of “crude protein” (Kjeldahl N × 6.25) are no longer adequate. The proteins of fresh forages may be considered in 3 main groupings (1) Fraction I leaf protein (2) Fraction 2 proteins and (3) Chloroplast membrane proteins.