EFFECT OF BARLEY SUPPLEMENT ON MICROBIAL FIBROLYTIC ENZYME-ACTIVITIESAND CELL-WALL DEGRADATION RATE IN THE RUMEN

Three ruminally cannulated dry cows were used in a Latin square design to investigate the relationship between microbial fibrolytic enzyme a ctivities and in sacco cell wall degradation of two gramineous bays, i n which cell wall content ranged from 510 g kg(-1) DM for the regrowth to 687 g kg(-1) DM for the late harvested hay. Animals were fed twice daily a diet consisting of wheat straw, cocksfoot hay and ground barl ey in the ratios 10:90:0 (w/w), 10:60:30 (w/w) and 10:30:60 (w/w). For each diet and each hay, the in sacco degradation of cell wall polysac charides and phenolic acids was determined. After 2 h and 23 h incubat ion time in the rumen, pH was measured in the bags, and fibrolytic act ivities (xylanase, avicelase, beta-glycosidases) of the microbial popu lation colonising bays in sacco were measured. Supplementation above 3 0% barley decreased the degradation rate of the cell wall polysacchari des, concomitantly with a decrease in polysaccharidase activities. The decrease in degradation rate was more marked for the regrowth than fo r the late harvested hay, for hemicelluloses than for cellulose and fo r ferulic than for p-coumaric acid. These differences did not appear t o be related to microbial activities, which were similar between hays and between polysaccharidases, but rather to differences in accessibil ity of cell wall components to microbial enzymes, related to the compo sition of the forage and the cell wall architecture.