VALIDATION OF IN-SACCO METHOD - INFLUENCE OF SAMPLING SITE, NYLON BAGOR RUMEN CONTENTS, ON FIBROLYTIC ACTIVITY OF SOLID-ASSOCIATED MICROORGANISMS

Three ruminally cannulated cows, fed twice daily with a 70:30 forage:c oncentrate diet, were used to investigate the differences in fibrolyti c activity of solid-associated microorganisms between nylon bags and r umen contents. Two different grass hays (regrowth and late harvested) were incubated in ruminal nylon bags. After 2 h or 23 h incubation tim e, pH was measured in bags and rumen contents, and enzymes of solid-as sociated microorganisms were extracted from bag residues and surroundi ng digesta by grinding, freezing, defrosting and sonication. Xylanase, avicelase, beta-D-xylosidase and beta-D-glucosidase activities were m easured. Activities were lower in bag residues than in rumen digesta, and differences were greater after 2 h than after 23 h incubation time . Causes of these differences are discussed, For each incubation time and each enzyme, the differences in solid-associated microorganisms ac tivities between rumen and bags contents were independent of the quali ty of hay in the bag, Thus the lower fibrolytic activity inside the ba gs may account for an underestimation of in vivo ruminal fiber degrada tion by the in sacco method, but this underestimation may be similar w hatever the nature and content of forage cell walls.