Effects of microwave irradiation on ruminal dry matter, protein and starch degradation characteristics of barley grain

This study evaluated effects of microwave irradiation (800 W) for 3, 5 and 7 min on dry matter (DM), crude protein (CP) and starch degradation characteristics of barley grain and to monitor the fate of its proteins in the rumen. Duplicate in situ bags of untreated or irradiated barley grain were incubated in the rumen of four non-lactating Holstein cows for up to 48 h. Proteins of untreated and irradiated bag residues were fractionated by gel electrophoresis. Irradiation for 3 min had no effect, but for 5 and 7 min decreased (P<0.05) the effective DM degradability. The washout fraction, and the degradation rate of CP, decreased (P<0.05) and the potentially degradable CP fraction increased (P<0.05) as irradiation period increased. Effective CP degradability of barley irradiated for 3, 5 and 7 min decreased (P<0.05) by 6%, 10% and 13%, respectively. Microwave irradiation increased (P<0.05) the washout fraction and decreased (P<0.05) the potentially degradable fraction and degradation rate of starch. Irradiation for 5 min had no effect on effective starch degradability, but for 3 and 7 min increased, and decreased it (P<0.05), respectively. From electrophoretic analyses, three major hordein fractions (B-, C- and D-hordein) occurred. In untreated barley grain, most hordein fractions had disappeared after 6 h of incubation, but in microwave irradiated barley, C- and D-hordein were not degraded until 12 h of incubation in the rumen. Microwave irradiation of barley grain for 3 min increased its starch degradability and, over 5 min, decreased the rate and extent of CP and starch degradation.