Chemical composition, secondary compounds, ruminal degradation and in vitro crude protein digestibility of gamma irradiated canola seed

Abstract

This study was completed to evaluate effects of gamma irradiation (γ-irradiation) at doses of 15, 30 and 45 kGy on ruminal degradability, in vitro crude protein (CP) digestibility, chemical composition and secondary compounds of canola seed (CS). Three ruminally fistulated bulls were used to measure ruminal in situ dry matter (DM) and CP degradability. Sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) was used to monitor protein subfractions and the fate of true proteins of γ-irradiated CS in the rumen. γ-Irradiation had no effect on chemical composition of CS, but phytic acid was eliminated completely at a dose of 30 kGy. γ-Irradiation decreased the total glucosinolate contents of CS ( P<0.001). There was a linear decrease in the washout fraction and linear increase in the potentially degradable fraction of DM ( P<0.001). Effective degradability (ED) of DM decreased linearly ( P<0.001) with increases in irradiation dose. γ-Irradiation increased ( P<0.001) the potentially degradable fraction of CP from 540 to 669 g/kg. γ-Irradiation reduced ( P<0.001) the degradation rate of the b fraction of CP. ED of CP decreased ( P<0.001) with increases in irradiation dose. γ-Irradiation at doses of 30 and 45 kGy, increased in vitro CP digestibility of undegraded CP remaining in bags incubated for 16 h in the rumen by 15 and 21%, respectively. Electrophoresis showed that napin subunits of untreated CS disappeared completely within the shortest incubation periods, whereas cruciferin subunits were degraded in the middle of incubation periods. At 30 and 45 kGy γ-irradiated CS, napin subunits were degraded in the middle of the incubation and cruciferin subunits were degraded at the longest incubation periods. γ-Irradiation seems to be effective in protecting CS proteins from ruminal degradation and reducing secondary compounds in CS at doses higher than 15 kGy.