RUMEN DEGRADATION AND INTESTINAL DIGESTION OF GRASS AND CLOVER AT 2 MATURITY LEVELS DURING THE SEASON IN DAIRY-COWS

A comparison was made of the effect of season and maturity on the in s itu ruminal breakdown and intestinal protein digestion in dairy cows b etween intensively N-fertilized grass (whole sward) and moderately N-f ertilized ryegrass and clover from a mixed sward. From May to Septembe r 1990, eight consecutive cuts were made, representing alternate harve sts of late and early swards. Limited effects of fertilizer-N on chemi cal and ruminal degradation characteristics and intestinal digestion o f grasses were observed. Clover had higher ash, crude protein (CP) and lignin and lower hemicellulose, cellulose and sugar contents than gra ss. Moreover, soluble fractions of organic matter (OM) and CP were hig her, and rumen-undegradable OM and CP fractions were lower. Soluble fr actions of grasses and clover decreased and undegradable fractions inc reased during the season. More mature swards showed increased undegrad able fractions. Degradation rates of OM and CP in clover were, respect ively, higher than or similar to those of grass. Seasonal effects on d egradation rates differed between grass and clover. Effectively rumen- degradable (g kg-1 DM) carbohydrates and CP, escaped protein and intes tinal digestion of escaped protein were higher in clover than in grass es. Inclusion of clover in swards may result in higher post-rumen prot ein supply. Supplementation of clover-based diets is suggested to comp ensate for an increased loss of N in the rumen.