Effects of acid-extrusion on the degradability of maize distillers dried grain with solubles in pigs

Commonly used feed processing technologies are not sufficient to affect recalcitrant non-starch polysaccharides (NSP) such as arabinoxylans present in maize distillers dried grain with solubles (DDGS). Instead, hydrothermal treatments combined with acid catalysts might be more effective to modify these NSP. The objective of this experiment was to investigate the effects of hydrothermal maleic acid treatment (acid-extrusion) on the degradability of maize DDGS in growing pigs. It was hypothesized that acid-extrusion modifies DDGS cell wall architecture and, thereby, increases fermentability of NSP. Two diets, containing either 40% (wt/wt) unprocessed or acid-extruded DDGS, were restrictedly fed to groups of gilts (n = 11, with 4 pigs per group; initial mean BW: 20.8 ± 0.2 kg) for 18 d and performance and digestibility were analyzed. Acid-extrusion tended to decrease apparent ileal digestibility (AID) of CP (~3 percentage units, P = 0.063) and starch (~1 percentage unit, P = 0.096). Apparent digestibility of CP and starch measured at the mid colon (2 percentage units, P = 0.030 for CP and 0.3 percentage units, P <0.01 for starch) and total tract (ATTD; 3 percentage units, P <0.01 for CP and 0.2 percentage units, P = 0.024 for starch) were lower for the acid-extruded diet compared with the control diet. Hindgut disappearance was, however, not different between diets indicating that reduced CP and starch digestibility were mainly due to decreased AID. Acid-extrusion tended to increase AID of NSP (6 percentage units, P = 0.092) and increased digestibility of NSP measured at the mid colon (6 percentage units, P <0.01), whereas, hindgut disappearance and ATTD of NSP did not differ between diets. Greater NSP digestibility was mainly due to greater digestibility of arabinosyl, xylosyl, and glucosyl residues, indicating that both arabinoxylan and cellulose degradability were affected by acid-extrusion. In conclusion, these results show that acid-extrusion did not improve degradation of DDGS for growing pigs. Although acid-extrusion seemed to facilitate more rapid degradation of NSP and shifted fermentation to more proximal gastrointestinal segments, total extent of NSP degradation was not affected. More than 35% of the NSP from DDGS remained undegraded, independent of technological processing. Enzyme technologies that specifically target ester-linked acetyl, feroloyl, or coumaroyl groups were identified to be of interest for future research.