Effects of roasting and electron beam irradiating on protein characteristics, ruminal degradability and intestinal digestibility of soybean and the performance of dairy cows

• Effect of two physical processing of soybeanwas examined in vitro and in vivo.
• Roasting and irradiating hadvaried effects onprotein fractions and degradability.
• Roasting increased the efficiency of protein utilization and milk yield.
• Feeding electron beam irradiation showed no influence on lactational performance.

Various methods of processing soybeans (SB) may help to decrease its extent of ruminal degradation, thereby providing more nutrients needed for high producing dairy cows. Two experiments (in situ and in vivo) were conducted to examine the effect of roasting and electron beam irradiating on ruminal degradability and intestinal digestibility of SB and performance of dairy cows. In the in situ trial, nylon bags of untreated (USB), roasted (RSB), and irradiated (ESB) soybean were incubated in the rumen of three non-lactating cows for up to 48 h. Additional samples of each SB product were also incubated for 12 h in the rumen; the residues from these bags were transferred to mobile bags, soaked in pepsin HCl, and then used for determination of intestinal digestibility. The results showed that the roasting processing was an effective method of changing the site of digestion from the rumen to the small intestine and therefore the amount of digestible crude protein (CP) in the small intestine can be increased. However, total tract disappearance of CP was not significantly different between USM and RSB. Irradiation of SB increased (P<0.05) protein solubility and the degradation rate of the potentially degradable fraction of protein, and decreased (P<0.05) the slowly degraded true protein (B3 fraction) compared to USB. Intestinal digestibility and total tract disappearance of CP were also lower (P<0.05) for ESB than USB and RSB. Proteins of untreated and treated SB residues were fractionated by sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE). Based upon electrophoretic patterns, the basic subunits of glycinin formed the major component of escaping protein in ESB while those in RSB samples were the subunits of glycinin and β-subunits of conglycinin. In the in vivo trial, nine lactating Holstein cows (610±23 kg and 141±4 d in milk) were used in a 3×3 Latin square design with 21-d experimental periods. Treatments had no effect on ruminal ammonia concentrations and blood urea nitrogen. Dry matter intake tended (P=0.11) to be lower in cows fed RSB diet compared to those fed USB and ESB diets. Roasting improved the efficiency milk yield of the lactating cows while irradiation had no impacts on milk production. In conclusion, roasting improved the efficiency of SB protein utilization and milk yield, whereas irradiation increased the rate of ruminal degradation of CP and had no effect on lactation performance of dairy cow.