Changes during growth in anatomical and chemical composition and in-vitro degradability of lucerne

Lucerne (alfalfa) was harvested at different stages of maturity and the plants classified according to a phenological scale. The main class was separated into anatomical parts and analysed for content of extractives and crude protein and in-vitro degradability. Whole crop samples were also analysed for polysaccharide residues, Klason lignin and in-vitro degradability of crude protein and polysaccharide residues. The composition of the plant changed during maturation with an increase of the stem fraction from 18.5% to 50.7% of dry matter and a corresponding decrease in the leaf fraction from 72.9% to 18.4% of dry matter. The leaf fraction changed least in content of extractives and crude protein and in-vitro degradability while in the stems all these paramaters decreased radically. Chemical analysis of residues after incubation with rumen liquor in vitro of whole crop samples revealed that the degradability of crude protein declined from about 90% to about 80% and of non-starch polysaccharides from about 90% to about 60% during maturation. Xylose was the least degradable polysaccharide residue at all harvests. Xylose residues also showed the greatest decrease in degradability during growth. A comparison showed that stage of development and harvest date were of practically equal value as predictor of crude protein content in lucerne.