ENZYME-ACTIVITIES OF RUMEN PARTICLES AND FEED SAMPLES INCUBATED IN-SITU WITH DIFFERING TYPES OF CLOTH

Three ruminally cannulated non-lactating dairy cows were used to inves tigate the effects of six different bag cloth types with pore size (mu m):free surface area (%) ratios of 200:45, 41:33, 16:5, 10:2, 6:5 and 1:2 respectively on the disappearance of grass silage DM and neutral- detergent fibre (NDF), and on particle-associated carboxymethylcellula se (EC 3.2.1.4; CMCase) and xylanase (EC 3.2.1.8) activities extracted from feed residues. Another objective was to compare microbial activi ty inside the bags and in rumen ingesta. Rumen incubation periods were 3, 6, 12, 24, 48 and 96 h. DM and NDF disappearance and particle-asso ciated enzyme activities were greatly reduced with the smaller pore si ze and/or open surface area. Re-analysing some of the data as a 2 x 2 factorial (pore size x free surface area) indicated that, generally, f ree surface area rather than pore size affected the disappearance of f eed components and particle-associated enzyme activities. Enzyme activ ities were highly correlated with NDF disappearance at 6-48 h of incub ation. Cumulative area under CMCase and xylanase activity curves expla ined 0.79 and 0.88 of the variation in NDF disappearance when differen t cloth type and 6-48 h incubation data were combined. Weighted mean e nzyme activities inside the bags were less than 0.35 those in rumen in gesta. The highest activity values inside the bags (24 or 48 h) were l ess than 0.50 those found in rumen ingesta. The lower microbial activi ty inside the bags explains the slower rates of NDF digestion reported with in situ techniques than with rumen evacuation techniques. The ge neral assumption of similar microbial activity inside the bags and in rumen ingesta is not justified by the present results, and caution mus t be taken in interpreting in situ results quantitatively for feed eva luation systems.