The effect of micronization of full-fat canola seed on digestion in the rumen and total tract of dairy cows

The effect of micronization of full-fat canola seed on dry matter disappearance (DMD) and total nitrogen disappearance (TND) in the rumen and intestine were investigated. Full-fat canola seed was left untreated (C) or micronized for 1.5 min (M), and left whole (CW, MW) or ground to pass through a 1.25-mm sieve (CG, MG). In vitro gas production from CW and MW were determined at 0, 1, 2, 3, 8, 12, 20, 24, 32, 48, 52, 68 and 72 h. For subsequent studies, CW was hand-cracked (CH) for comparison against MW. In situ DMD and TND from CH, MW, CG and MG were determined after 0, 2, 4, 8, 16, 24, 48 and 96 h of ruminal incubation. The mobile nylon bag technique was used to estimate intestinal digestion (DM and N disappearance) of samples incubated in the rumen for 16 h and in acid-pepsin for 1 h. Scanning electron microscopy revealed the pattern and extent of seed coat rupture from hand-cracking and from micronization to be similar, but micronization-mediated changes to the internal structures were evident in ground samples. Micronization increased (P < 0.05) in vitro gas production from whole canola seed (CW vs. MW), but relative to CH, DMD and TND from MW were lower (P < 0.001) in situ and in the whole digestive tract (P < 0.001). Estimated intestinal DMD and TND did not differ (P > 0.05) between CH and MW. Ruminal DMD and TND from ground seed were reduced (P < 0.05) by micronization (CG vs. MG) in the rumen, but intestinal DMD and TND were increased (P < 0.05 and P < 0.01, respectively), thus in the whole digestive tract, these values did not differ (P > 0.05) between treatments. Micronization reduced potential ruminal protein degradability (P < 0.05) and effective ruminal protein degradability (P < 0.01) of full-fat canola, and in combination with grinding, increased the proportion of protein digestion in the intestine. Key words: Micronization, full-fat canola seed, digestibility, rumen, dairy cow, in situ