Composition and short chain fatty acid formation of pig fecal microbiota during growth on predigested wheat and rye in vitro

BackgroundWhile wheat is the most commonly used cereal in pig feeding, rye has gained renewed interest as a component in pig diets due to its positive effects on gut health. The effects of distinct cereal sources on the composition and functionality of gut microbiota are, however, poorly investigated so far. In vitro studies offer a valuable approach to gain detailed insights on this matter, however, require a substrate that closely mimics the conditions found in the large intestine. In this study, we performed predigestion of cereal substrates using ileo-cecally fistulated minipigs simulating the upper gastrointestinal digestion. The composition of microbiota, total cell counts, and short chain fatty acid concentrations after a 24-hour incubation were analysed. Results were compared to cultures containing native substrates. ResultsBoth acetate and propionate concentration were significantly higher in predigested rye compared to predigested wheat (8.17 {+/-} 2.71 vs. 6.55 {+/-} 2.16 mmol/l and 3.40 {+/-} 0.436 vs. 2.64 {+/-} 0.337 mmol/l, respectively), whereas butyrate concentrations were not different. Substantial differences were observed between native and predigested substrates with a higher butyrate production on the former. Bacterial cell counts were higher in predigested substrates and elevated in rye cultures compared to respective wheat incubations. Bacterial communities differed markedly between the two predigested cereals as well as between native and predigested substrates. Several known butyrate and propionate producers - for example Agathobacter, Blautia, Coprococcus, Mediterraneibacter and Roseburia - grew significantly more on predigested rye than on predigested wheat. Bifidobacterium, Clostridium sensu stricto, and Succinivibrio were significantly more abundant on native substrates compared to their predigested forms. ConclusionRye promoted higher production of acetate and propionate compared with wheat along with a distinct bacterial community composition. Predigestion of substrates was crucial in in vitro experiments for gaining adequate insights into growth and substrate degradation by colonic microbiota.