In vitro ruminal fermentation parameters of canola meal protein in response to incremental doses of gamma irradiation

Rapid ruminal degradation of canola meal (CM) limits its feed value for high-producing ruminants. Attempts to reduce ruminal degradability of CM through gamma irradiation have generated conflicting results. While this strategy has the potential to reduce CM degradability, the optimal radiation dose is unknown for this valuable co-product. Therefore, this in vitro ruminal fermentation study was designed to evaluate the efficacy of gamma irradiation to protect CM protein from ruminal degradation. Canola meal was irradiated at 0 (CM0), 15 (CM15), 30 (CM30), 45 (CM45), 60 (CM65), 75 (CM75), and 90 kGy (CM90). Irradiated CM was then analysed for proximate composition and incubated with rumen fluid to determine in vitro degradability of dry matter (DMD) and nitrogen (ND). The data were evaluated for linear and quadratic effects using response surface regression analysis. Neutral detergent fibre and acid detergent fibre linearly decreased as irradiation dosage increased. Quadratic responses were observed for total nitrogen (N) content, DMD12, and DMD36 in response to increasing irradiation dosage. Gamma irradiation linearly increased the rapidly soluble fraction (a) and effective degradability (ED) of dry matter. There were no irradiation effects on ND12, ND36, ND48, fractional rate constant (c), and potential degradability, but significant quadratic trends were observed for ND24, a, slowly degradable fraction (b), and ED of N. It was concluded that although gamma irradiation altered the chemical composition of CM, it was not an effective method to protect CM from extensive ruminal degradation