Flaxseed meal and oat hulls supplementation: impact on dietary fiber digestibility, and flows of fatty acids and bile acids in growing pigs.

The present study was conducted to determine the effects of adding flaxseed meal (FM) or oat hulls (OHs) in pigs' diets on digestibility of dietary fiber (DF) and fatty acids (FAs), and gastrointestinal flows of FA and bile acids (BAs). Twelve Genesus [(Duroc ♂ × Yorkshire-Landrace ♀)] cannulated barrows (initial BW: 35.1 ± 0.44 kg) were individually housed and offered diets in a two-period cross-over design (n = 8). In each period, four pigs were assigned to one of the three corn-soybean meal-based diets without (control), or with FM or OHs. Soybean oil was added in each diet to give an FA content of 4.56%, 6.02%, and 6.05 % in the control, FM, and OH diets, respectively. Feces and ileal digesta contents were collected to determine apparent ileal (AID), total tract (ATTD) digestibility of dietary components and flows of FA and BA. Pigs fed the control diet had greater (P < 0.05) AID of SFA and insoluble DF and ATTD of SFA than pigs offered the OH and FM diets. The AID of total FA and MUFA in FM diet-fed pigs was lower (P = 0.02) compared to those fed the control and OH diets. The ATTD of CP, NDF, insoluble and total DF was lower (P < 0.05) in pigs fed the OH diet than in pigs that consumed the control and FM diets. In the terminal ileum, pigs fed OH and FM diets excreted more (P < 0.05) primary BA and all secondary BA (except lithocholic acid) compared to control diet-fed pigs. The intestinal flows of lithocholic acid in pigs fed the FM diet were higher (P < 0.05) than in pigs offered the control diet. Pigs fed FM and OH diets excreted more (P = 0.001) fecal ursodeoxycholic and total BAs compared to pigs that consumed the control diet. The ileal flows of eicosapentaenoic and erucic acids in pigs fed the FM and OH diets were greater (P < 0.05) than in pigs fed the control diet. The flow of all SFA, and palmitoleic, palmitelaidic, oleic, nervonic, linoleic, eicosapentaenoic, erucic, docosatetraenoic and docosapentaenoic acids in feces were greater (P < 0.05) in OH diet-fed pigs compared to pigs fed other diets. In conclusion, addition of FM and OHs in pig diets reduced FA digestibility, increased gastrointestinal flows of FA and excretion of BA. Dietary supplementation with FM and OHs induces variable effects on digestibility of DF fractions and fecal flows of unsaturated FA. Future studies are needed to quantify the contribution of endogenous FA losses from the host to gastrointestinal flows of FA.