B.P. Glenn

Effect of stage of maturity of alfalfa and orchardgrass on in situ dry matter and crude protein degradability and amino acid composition

Abstract Four maturities of alfalfa (early bud, early, mid and full bloom) and orchardgrass (vegetative, early head, full head and anthesis) were used to test the effect of stage of maturity on in situ rumen dry matter, crude protein degradation and amino acid composition. Two rumen fistulated Holstein cows were used in a 2 × 2 Latin square design with forage species as treatments. Cows were fed a basal diet consisting of 33% corn silage, 17% alfalfa haylage and 50% concentrate on a dry matter basis. Forages were incubated in situ in polyester bags at eight different times (0–96 h) in the rumen. Mean effective degradabilities for both crude protein (82.3 vs. 74.5%) and dry matter (67.6 vs. 63.4%) were higher for alfalfa than for orchardgrass, respectively. Crude protein degradability decreased from 84.8 to 80.4% in alfalfa and from 78.0 to 69.6% in orchardgrass with increasing stage of maturity. Corresponding changes in effective dry matter degradability with increasing stage of maturity declined from 72.9 to 61.9% in alfalfa and from 68.6 to 56.1% in orchardgrass. Most of the depression in rumen degradability of both crude protein and dry matter with increasing stage of maturity could be explained by increases in the indigestible fraction of the forage as rates of digestion were not readily affected by stage of maturity. Individual amino acids declined with increasing stage of maturity of forage as crude protein declined but there was no change in the relative proportions of individual amino acids due to stage of maturity within forage.