Influence of non-fibrous carbohydrate and degradable intake protein on fermentation by ruminal microorganisms in continuous culture

Four continuous culture fermenters were used in a 4 x 4 Latin square design to evaluate the effects of dietary non-fibrous carbohydrate (NFC) and ruminally degradable intake protein (DIP) on fermentation by ruminal microorganisms. Four diets, arranged in a 2 x 2 factorial, were formulated to contain either 25 or 40% NFC and 50 or 70% of dietary CP as DIP. Dietary DM contained 32% corn silage, 20% alfalfa-grass hay, and 48% concentrate. Solvent-extracted or lignosulfonate-treated soybean meal were used to alter DIP and contributed 40% of dietary CP. Corn or soybean hulls were included at 28% of dietary DM to alter NFC levels. Percentage of true OM digestion was similar (P > .05) among diets but NDF and total nonstructural carbohydrate digestion were inversely related depending on NFC content of the diet. Amylolytic bacterial concentrations (cells/milliliter) were lower (P = .03) in fermenters supplied with 25% NFC diets, resulting in less (P = .0001) total nonstructural carbohydrate digestion. Cellulolytic concentrations were similar (P > .05) among diets despite an increase (P = .002) in NDF digestion with 25% NFC diets. Total viable bacterial concentrations tended to decrease (P = .11) with 50% DIP diets, inducing a decline (P = .03) in total VFA production (millimoles/day). Reduced degradation of CP in 50% DIP diets (P = .008) increased outflow of total amino acid (P = .07) and individual outflows (P < .05) of glutamic acid, aspartic acid, arginine, histidine, and lysine. Few interactions occurred for the parameters measured despite the controlled nature of the fermentation in the current experiment. The preponderance of significant main effects illustrates that ruminal fermentation may not be improved by synchronization of energy and N release but may more likely be limited by either energy or N alone.