Effects of Extruded Soybeans and Forage Source on Fermentation by Rumen Microorganisms in Continuous Culture

Continuous culture fermenters were used to evaluate effects of extrusion of whole soybeans and changes in forage composition of diets on microbial fermentation. Treatments were arranged in a 2 × 4 factorial design with soybeans (raw or extruded) and dietary treatment (ratio of alfalfa hay to corn silage; 82:18, 61:39, 43:57, and 27:73 of dietary forage) as main effects. Soybeans constituted 9.6, 14.4, 19.2, and 23.9% of DM for each of the respective dietary treatments. True digestion of DM, ADF, and NDF was unaffected by processing of soybeans or dietary treatment, but true digestion of OM decreased as concentration of corn silage and soybeans increased. Total VFA concentration was unaffected by source of soybeans or dietary treatments; however, molar concentration of butyrate decreased in fermenters supplied with diets containing extruded soybeans. Degradation of CP was not influenced by soybean source but decreased as the concentration of corn silage and soybeans increased. Bacterial N output decreased, and dietary N flow from the fermenters increased, as concentration of corn silage and soybeans increased. Changes in the ratio of alfalfa hay to corn silage and alteration of dietary soybean concentration affected true OM digestion and dietary CP degradation, but extrusion of whole soybeans had little effect on fermentation.