EFFECT OF THE DEGRADATION OF ORGANIC-MATTER AND CRUDE PROTEIN ON RUMINAL FERMENTATION IN DAIRY-COWS

The potential of the dacron bag technique to assess fluctuations in ru minal metabolites was studied using 40 Israeli-Friesian dairy cows ass igned to an experiment with a 2 x 2 factorial design. Diets contained a low (62%) or high (65%) percentage of ruminally degradable CP and a low (55%) or high (59%) percentage of ruminally degradable OM. Metabol ites were monitored before feeding and at 3 and 6 h postfeeding. Befor e feeding, total VFA and propionate were higher, and acetate and pH we re lower, in diets containing a high percentage of ruminally degradabl e OM than in diets containing a low percentage of degradable OM. By 3 h pose feeding, acetate, butyrate and pH were lower, and propionate wa s higher, in the diets containing a high percentage of ruminally degra dable OM than in the diets containing a low percentage of ruminally de gradable OM. By 6 h postfeeding, propionate was higher, and acetate wa s lower, in diets containing a high percentage of ruminally degradable OM than in diets containing a low percentage of ruminally degradable OM. In the diets with a high percentage of ruminally degradable OM, be fore feeding and by 3 h postfeeding, ammonia concentrations were highe r and lower, respectively, relative to the diets containing a low perc entage of degradable OM. Milk yield and composition and DMI were simil ar among treatments. The correlation was good between the degradabilit y data obtained by the dacron bag technique and the meal-induced varia tions in ruminal metabolites. The lack of a positive yield response to controlled fluctuations in ruminal metabolites may be related to surp lus CP intake.