Effect of ethanol concentration on the kinetics of ruminal degradation of soybean meal

Effects of ethanol treatment on ruminal in situ degradation kinetics of dry matter (DM) and crude protein (CP) of soybean meal (SBM) were determined. Soybean meal samples were soaked in 500, 600 or 700 ml/l ethanol solutions for 2 h. Duplicate nylon bags of untreated or treated SBM were suspended in the rumen of four non-lactating Holstein cows for up to 48 h, and resulting data were fitted to non-linear degradation model to calculate degradation parameters of DM and CP. Intestinal CP digestibility was measured using the mobile nylon bag technique. Proteins of untreated and treated bag residues were fractionated by gel electrophoresis. There were differences (P<0.05) for DM and CP degradation parameters between untreated and ethanol treated SBM. Regardless of the concentration, ethanol treatments applied to SBM decreased the washout fraction, the estimated rate of CP degradation, and the effective protein degradation (EPD) compared to untreated SBM. The lowest estimated rate of CP degradation and the calculated EPD were observed when SBM was treated with 600 ml/l ethanol solution. Extending the ethanol concentration over 600 ml/l to SBM was considered excessive. Ethanol treatments increased (P<0.05) the intestinal mobile bag digestibility of ruminally undegraded CP. At concentration of 500, 600 and 700 ml/l, digestibility of CP increased by 4, 12 and 13% compared to untreated SBM, respectively. Electrophoretic analyses of untreated, 500, 600 and 700 ml/l ethanol treated SBM revealed that two of the subunits of β-conglycinin (ά and α) had been degraded completely after 2, 6, 8 and 8 h, whereas the β subunit of this protein has been degraded after 4, 8, 12 and 12 h, respectively. In untreated SBM, the acidic and basic subunits of glycinin had been degraded in 8 and 12 h of incubation, but in treated SBM had not been degraded even after 48 h of incubation. Based upon these results, treatment of SBM with 600 ml/l ethanol solution had the greatest potential to increase rumen undegradable protein.