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Effects of Solids and Liquid Flows on Fermentation in Continuous Cultures. I. Dry Matter and Fiber Digestion, VFA Production and Protozoa Numbers^1,2,

University of Maine⁴, Orono 04473

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.

¹ Supported in part by Agway, Inc., Syracuse, NY.

² The authors gratefully thank Dr. M. R. Stokes for his assistance in the review and evaluation of these data.

² Present address: Dept. of Anim. and Vet. Sci., West Virginia Univ., Morgantown 26506.

⁴ Dept. of Anim. and Vet. Sci.

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