Effects of microwave irradiation on ruminal degradability and in vitro digestibility of canola meal

This study was completed to evaluate effects of 800 W microwave irradiation for 2, 4 and 6 min on ruminal dry matter (DM) and crude protein (CP) degradation parameters of canola meal (CM). Ruminal nylon bags of untreated or treated CM were suspended in the rumen of three Holstein steers for up to 48 h and resulting data were fitted to non-linear degradation model to calculate effective rumen degradation (ERD). Effective degradability of DM linearly (P<001) decreased as irradiation time increased. There was a linear decrease in the water soluble fraction and a linear increase in the potentially degradable fraction of CP (P<0.001). Microwave irradiation for 2, 4 and 6 min decreased ERD of CP at rumen outflow rate of 0.05 h−1 by 21, 24 and 29% units, respectively. Although there were differences for ERD of CP between treatments, there were not, in general, explained by polynomial orthogonal contrasts. Microwave irradiation for 2 and 4 min increased in vitro CP digestibility of ruminally undegraded CM at 8 and 12 h pre-incubation (linear effect, P<0.001) and 24 h pre-incubation (quadratic effect, P<0.001). Microwave irradiation for 6 min decreased in vitro digestibility of CP compared to 4 min. Electrophoresis results showed that napin sub-units of untreated CM disappeared completely within the shortest incubation period, whereas cruciferin sub-units were degraded in the middle of incubation period. In 4 min microwave irradiated CM, napin subunits were degraded in the middle of incubation and cruciferin subunits were degraded in the longest incubation period. In conclusion, CM proteins appeared to be effectively protected from ruminal degradation by a 4 min microwave irradiation.