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

Abstract

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 (C W , M W ) or ground to pass through a 1.25-mm sieve (C G , M G ). In vitro gas production from C W and M W were determined at 0, 1, 2, 3, 8, 12, 20, 24, 32, 48, 52, 68 and 72 h. For subsequent studies, C W was hand-cracked (C H ) for comparison against M W . In situ DMD and TND from C H , M W , C G and M G 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 (C W vs. M W ), but relative to C H , DMD and TND from M W 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 C H and M W . Ruminal DMD and TND from ground seed were reduced (P < 0.05) by micronization (C G vs. M G ) 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