The interactions between dietary fiber and lipid sources alter the predicted production and absorption of caecal and colorectal volatile fatty acids in growing pigs

A combination of in vivo and in vitro fermentation methodologies was used to determine the interactive effects of dietary fiber (DF) and lipid types on volatile fatty acids (VFA) production and absorption, and organic matter (OM) fermentability in the cecum and colorectal tract of pigs. Eight ileal- and caecalcannulated Yorkshire barrows were fed either pectinor cellulose-containing diets that were supplemented with either corn oil or beef tallow in two independent Youden squares with a 2×2 factorial arrangement of treatments (n = 6). Ileal and caecal digesta were collected, freeze-dried and fermented using inoculum from fresh caecal digesta and feces, respectively, to determine VFA production and absorption, and fermentability of OM. There were interactions (P < 0.001) between DF and lipid types observed in which the addition of corn oil increased the quantity of caecal and colorectal acetic acid production and caecal acetic absorption, caecal butyric production, predicted caecal OM fermentability, and the predicted colorectal propionic acid in pectin diets but did not have effects in cellulose diets. The addition of beef tallow increased (P < 0.001) the production of caecal butyric and propionic acids during in vitro fermentation in cellulose diets and fermentability of OM in pectin diets. The interactions between DF and lipids on gastrointestinal fermentation largely depends on the degree of saturation of fatty acids in dietary lipids. The addition of beef tallow selectively decreased the production and absorption of individual SCFA in pectin and cellulose diets but increased caecal butyric and propionic acid production in cellulose diets and the fermentability of OM in pectin diets.