When evaluating protein degradability in canola meal (CM) produced in 2011 and 2012 we observed that CM from different processing plants differed in rumen-degraded protein (RDP) and rumen-undegraded protein (RUP), estimated using the Michaelis-Menten inhibitor in vitro method (MMIIV). However, these analyses were conducted in 2 different years and may have been influenced by methodological changes over time (e.g., degradative activity of rumen inoculum may have altered between years). Three CM samples were collected from each of 12 Canadian production plants in each of 2 years (2013 and 2014; total = 72). Meals were analyzed chemically and for protein degradation rate, RDP and RUP by MMIIV, assuming passage rates of 0.16 and 0.06/h for soluble and insoluble proteins, respectively (Colombini et al., J. Dairy Sci. 94:1967–1977, 2011). Half of the meals from both years were analyzed in each of 3 MMIIV incubations; a total of 6 incubations were conducted. Differences among plants and years were assessed with the Proc Mixed procedure of SAS, and LSM over all plants for each year are in Table 1. As seen in 2011 and 2012, there were large differences in RUP among plants (data not shown). There were differences by year (P ≤ 0.04) in DM and protein fraction degraded at t = 0 (FD₀); CP in CM from 2013 was 1.8 percentage units greater than 2014 (P < 0.01). Theta (unadjusted degradation rate) was not different between years (P = 0.50). However, adjusting Theta for FD₀ resulted in differences in degradation rate by year (P = 0.03) and trends (P = 0.06) for differences in RDP and RUP. The results suggest that apparent differences among production years in RUP content of CM may be due to small differences in protein already degraded before incubation. Table 1. Composition and degradability of canola meals from 2 years

Trait1	2013	2014	SEM	P-value
DM, %	90.9	90.4	0.15	0.04
CP, % of DM	42.4	40.6	0.22	<0.01
Insoluble-N, % of TN	71.5	72.7	0.55	0.14
Soluble-N, % of TN	28.5	27.3	0.55	0.14
FD0, % of TN	2.4	1.8	0.13	0.01
Theta, /h	0.154	0.156	0.0078	0.50
Adjusted degradation rate, /h	0.143	0.147	0.0078	0.03
RDP, % of CP	64.5	65.0	1.18	0.06
RUP, % of CP	35.5	35.0	1.18	0.06

¹TN = total N; FD₀ = protein degraded at t = 0; Theta = unadjusted degradation rate.