Brief Incubations of Mixed Ruminal Bacteria: Effects of Anaerobiosis and Sources of Nitrogen and Carbon

Abstract

A series of brief in vitro incubations with mixed rumen bacterial populations was conducted. Aerobic, aerobic plus cysteine-sulfide, and anaerobic plus cysteine-sulfide treatments using either McDougall's or Starvation-survival buffer were compared for their effectiveness in preparing a mixed rumen bacterial inoculum from rumen contents. The results showed that the absence of strict anaerobiosis resulted in partial loss of cellulolytic and amylolytic bacterial groups. In incubations containing a mixture of carbohydrates and various nitrogen sources, urea plus acid-hydrolyzed casein was the best for maintaining normal proportions of carbohydrate-specific bacterial groups and appeared to enhance growth of cellulolytic and xylanolytic groups. With urea plus acid-hydrolyzed casein as the nitrogen source, effects of individual carbohydrate sources were monitored. Glucose, cellobiose, and soluble starch incubations were predominated by Streptococcus bovis-like bacteria within 3 h and resulted in disappearance of the cellulolytic bacterial group. In contrast, pectin or xylan plus xylose as carbon sources allowed a normal, rumen-like fermentation to continue and enhanced growth of cellulolytic and xylanolytic groups. The importance of these findings in relation to research with mixed ruminal bacteria is discussed. © 1983, American Dairy Science Association. All rights reserved.