Rigid pectin-cellulose-lignin matrix limits fermentation of canola (Brassica napus) meal polysaccharides in pigs

Degradation of non-starch polysaccharides (NSP) from canola meal (CM) is rather low (~60%) compared with NSP from other sources, such as soybean meal (~85%). Feed processing technologies might be used to improve degradability of NSP, but developing targeted technologies requires insight in the recalcitrant NSP-structures in CM. To identify the limiting structures in degradation of NSP from CM, undegraded carbohydrate structures from ileum, cecum, colon, and feces from pigs were studied in depth. A diet, containing 40 % (w/w) CM as the only NSP-source, was fed to growing pigs (gilts; initial BW: 20.8 ± 2.4 kg) for 14 days. Feces were collected during four days after which animals were euthanized to collect digesta samples. Ileal digestibility of NSP from CM was 22 % and total tract digestibility 68%. Water-soluble NSP were found to be almost completely fermented. Nearly 50 % of the unfermented carbohydrate structures in feces were found to be tightly bound pectins (e.g. rhamnogalacturonan and arabinan), xyloglucan, and cellulose, presumably, present as a rigid cellulose-lignin network in CM. The other half consisted of smaller uronyl-rich carbohydrates that were released during alkaline extraction of the feces. Presumably, these carbohydrates were present via ester-linkages or hydrogen-bonding within the cellulose-lignin network in the original CM. Apparently, microbiota present in the pigs’ digestive tract were able to partly degrade those carbohydrates but still complete fermentation was hindered by ester- or H-bonds.