Chemical and ruminal in vitro evaluation of Canadian canola meals produced over 4 years1

To test the effects of year and processing plant on the nutritional value of canola meal (CM), 3 CM samples/yr were collected from each of 12 Canadian production plants over 4 yr (total = 144). Samples of CM were analyzed for differences in chemical composition and for in vitro ruminal protein degradability using the Michaelis-Menten inhibitor in vitro (MMIIV) method. In the MMIIV method, protein degradation rate (kd) was estimated by 2 methods: from net release (i.e., blank corrected) of (1) ammonia plus AA determined by o-phthaldialdehyde fluorescence (OPAF) assay or (2) ammonia, AA, plus oligopeptides determined by o-phthaldialdehyde absorbance (OPAA) assay; rumen-undegradable protein (RUP) was computed assuming passage rates of 0.16 and 0.06/h for, respectively, soluble and insoluble protein. Casein, solvent soybean meal (SSBM), and expeller soybean meal (ESBM) were included in all incubations as standard proteins. Differences among years and plants were assessed using the mixed procedures of SAS. Small but significant differences were found in CM among years for chemical composition, including N solubility; some of these differences may have been related to changes in our analytical methods over time. However, adjustment of degradation activity of individual in vitro incubations based on the mean degradation activity over all incubations yielded kd and RUP that did not differ by year using either assay. Simultaneously incubating CM samples from 2 yr in the same in vitro runs confirmed that no year effects existed for kd or RUP. Differences existed in chemical composition of CM among the 12 processing plants over the 4 yr of sample collection. Moreover, consistent differences in kd and RUP were observed among plants: kd ranged from 0.069 to 0.113/h (OPAA assay) and 0.075 to 0.120/h (OPAF assay), and RUP estimates ranged from 51 to 43% (OPAA assay) and 49 to 41% (OPAF assay). Regression of kd on insoluble N content of CM yielded correlation coefficients (R2) = 0.40 (OPAA assay) and 0.42 (OPAF assay), and regressions of kd on NDIN and N-fraction B3 yielded R2 < 0.02. Mean estimates from both OPAA and OPAF assays for casein, SSBM, ESBM, and CM were, respectively, kd = 0.764, 0.161, 0.050, and 0.093/h and RUP = 18, 33, 56, and 45%. A range of 8 percentage units from lowest to highest RUP suggests that substantial differences exist in metabolizable protein content of CM produced by different processing plants.