Effects of Solids and Liquid Flows on Fermentation in Continuous Cultures. I. Dry Matter and Fiber Digestion, VFA Production and Protozoa Numbers2

Abstract

Effects of solids retention times (SRT) of 14.3, 22.0 and 29.7 hr and dilution rates (D) of .07, .11 and .15 volumes/hr on several rumen fermentation parameters were investigated with a dual effluent continuous culture system. The study was conducted as a split-plot randomized complete block design, with SRT as the main treatment and D as the subtreatment. A pelleted diet consisting of 60% grain mixture and 40% hay crop silage was fed at a rate that increased with decreasing SRT. The pH ranged from 4.57 to 6.78 within the fermenters and increased as D increased, but decreased as feed input increased. Volatile fatty acid (VFA) production per 100 g dry matter (DM) digested increased with increasing D at the lowest SRT but showed little or no increase between D's of .11 and .15/hr for the 22.0- and 29.7-hr SRT's. Values ranged from 4.23 to 6.26 mmoles VFA/g DM digested. Increases in both SRT and D resulted in an increase in the molar proportion of acetate and a decrease in the molar proportion of propionate, in most instances. Digestibility coefficients for DM, cellulose, acid detergent fiber, neutral detergent fiber and hemicellulose ranged from 33.32 to 78.03%, 8.17 to 69.05%, 0 to 61.54%, 0 to 64.24% and 0 to 67.79%, respectively. All digestibilities tended to increase with increasing SRT and D. However, most digestibilities reached a plateau at 22.0 hr at D's of .11 and .15/hr; increasing SRT to 29.7 hr resulted in little or no increase at these D's. Protozoa were maintained at approximately 1.0 x 10⁴ protozoa/ml only when the SRT was 29.7 hours. At SRT's of 14.3 and 22.0 hr, protozoa continued to decline throughout the fermentation period. Copyright © 1980. American Society of Animal Science . Copyright 1980 by American Society of Animal Science.