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This study was carried out to determine soybean meal dry matter (DM), crude protein (CP), true protein (TP) and protein subunits degradation characteristics by using nylon bags and SDS-PAGE techniques. Nylon bags containing five grams of defatted soybean meal (in duplicates) were suspended in the rumen from 0 to 48 h. After incubation, bags were removed, washed and freeze dried. DM, CP, TP, protein subunits and densitometric scanning patterns in each sample were determined. The rumen DM, CP, TP and subunits summation degradability of soybean meal at rumen outflow rates of 2, 5 and 8 % were 83.3, 71.4, 63.5% (for DM); 82.7, 68.3, 59.2% (for CP); 82.7, 69.2, 60.3% (for TP) and 83.7, 70.1, 60.9 (for summation of subunits) respectively. No significant differences (P>0.05) among effective rumen degradability values in CP, TP as well as summation of subunits components were observed at different rumen outflow rates. From it is revealed that, slab gel analysis, soybean meal proteins are composed of two major components, ?-conglycinin and glycinin, accounting for approximately 31 and 38.8 percent of the total meal protein, respectively. Both proteins are multisubunits. The molecular weight of 90.5, 71.5, 55.2 KDa for ?, ?, ? subunits of ?-conglycinin and 37.6, 19.8 KDa for acidic and basic states of glycinin were estimated in this study. Electrophoretic and densitometric analysis of protein residues revealed that conglycinin ? & ? subunits were degraded completely within 2 h, whereas ? subunit of ?-conglycinin (12 h) as well as the acidic (24 h) and basic (48 h) polypeptide components of glycinin were more resistant to degradation. In addition, the basic polypeptides in glycinin were shown to be more resistant to degradation than acidic polypeptides. In vitro digestibility of CP residues was increased as incubation time increased. Digestibility values of CP residues at 0, 8, 12 and 48h of incubation time were 69.7, 83.2, 94.2 and 96.8 percent, respectively. In conclusion, through SDS-PAGE it was indicated that the basic subunits of glycinin make an appreciable contribution to metabolizable protein when soybean protein is fed to ruminants. This methodology can not only be used to predict ruminal degradation directly and accurately, but also to determine and assess the type of proteins that will escape the rumen.