Effect of dried fermentation biomass on microbial fermentation in continuous culture and in vitro intestinal digestibility

The objective of the current experiment was to determine if fermentation biomass (FB), a dried bacterial by-product derived from lysine production (Ajinomoto Heartland, Inc.) can be used as a protein source in ruminant diets. Eight dual-flow continuous culture fermenters were inoculated with rumen fluid and used during one experimental period consisting of a 7-d adaptation period followed by 3 sampling days. Microbial substrate was provided by one of two isonitrogenous diets, CON or DFB. In CON, soybean meal (SBM) provided 57% of total CP, and in DFB, SBM and FB provided 12 and 45% of total CP, respectively. CON contained 3% molasses, 16% ground corn, 13% grass hay, 48% corn silage, and 20% SBM on a DM basis; DFB contained 3% molasses, 18.4% ground corn, 13% grass hay, 50% corn silage, 8.5% SBM, and 6.7% FB. On sampling days, liquid and solid effluent were collected, combined, and homogenized to be used for chemical analysis and in vitro estimation of intestinal digestibility (ID). Treatment did not affect average, maximum, or minimum fermenter pH. There was no effect on apparent or true OM, NDF, or ADF digestibility (%). Total and branched-chain VFA as well as acetate (mM) were higher in CON, and isobutyrate concentration (mol/100 mol) tended to increase with CON treatment. Source of N had no effect on total, dietary, or bacterial-N flows. Addition of FB decreased NH₃-N flow from 0.4 to 0.2 ± 0.05 g/d and tended to decrease effluent NH₃-N concentration from 17.1 to 9.7 ± 2.21 mg/100 mL. His and Met flows increased from 0.48 to 0.53 ± 0.012 and 0.18–0.20 ± 0.005 g/d, respectively, when FB partially replaced SBM in the diet, but there were no effects on other AA or total AA flows. There was a trend in percent non-essential AA input (CON = 73.6% vs. DFB = 82.2%; SE = 2.83) in effluent; however, there was no effect on percent of essential or total AA input in effluent. Effluent from the DFB treatment was higher in ID than CON (CON = 70.4% vs. DFB = 79.6%; SE = 1.64), although there was no difference in estimated amount of protein available for intestinal absorption (g). These results indicate that FB elicited a similar response in N metabolism and AA flows to SBM but had a greater estimated ID and depressed VFA production, and has potential use as a protein source in ruminant diets.