PSI-16 - Effects of dietary protein and fiber concentration on nutrient digestibility, fermentation products, and microbiome profile in pigs fed a blend of branched-chain volatile fatty acids

Abstract: Branched-chain volatile fatty acids (BCVFA) inclusion in ruminant diets has been associated with increased fiber degradability by modulating microbial populations in the rumen. In swine, our previous study demonstrated that BCVFA supplementation at 1% in a normal protein, low-fiber diet fed to growing pigs increased fiber and amino acids (AA) digestibility. This study evaluated the interactive effects of dietary protein and fiber concentration on apparent ileal (AID) and total tract nutrient digestibility (ATTD), microbiota profiling, and fermentation products in BCVFA-fed pigs. Fourteen cannulated pigs (20.4 ± 1.4 kg) were used in a 5-period crossover design and assigned to one of six experimental diets (at least 11 observations per diet). Experimental diets were organized in a 2 × 2 + 2 treatment arrangement, consisting of BCVFA-supplemented diets (isobutyrate, isovalerate, and 2-methyl butyrate, 1:1:1) at 1%, with varying protein [low (LP; 15%) or normal (NP; 19%) protein] and fiber content [low (LF; 11% neutral detergent fiber (NDF) or high (HF; 17% NDF)]. A positive control with LP-LF (PC) and a negative control with NP-HF, both without BCVFA were included. Each experimental period consisted of 14 d: 10 d for acclimatization to the diets, 2 d for fecal collection, and 2 d for digesta collection. Diets, fecal, and ileal digesta samples were analyzed for gross energy, crude protein (CP), fiber composition, AA, and titanium. The concentrations of volatile fatty acids (VFA) and ammonia were analyzed in digesta and fecal samples. Additional fecal samples were collected for microbial analysis. Data were analyzed as a 2 x 2 factorial design using the PROC MIXED procedure in SAS and contrasts were used to determine the effects of BCVFA supplementation. Pigs fed BCVFA-supplemented NP-HF diets had the greatest AID for crude fiber, acid detergent fiber (ADF), acid detergent lignin, cellulose, and hemicellulose, and the greatest ATTD for ADF (P< 0.05). The AID of AA was increased (P< 0.05) in pigs fed PC diet compared to LP-LF BCVFA-supplemented diet (P< 0.05). The absence of BCVFA effect in LP-LF diets could be attributed to a lack of nitrogen availability for cellulolytic bacteria. There were no interactions (P>0.05) between fiber and protein levels for VFA in ileal and fecal samples. Feeding high-fiber diets supplemented with BCVFA resulted in higher (P < 0.05) concentrations of acetic, propionic, butyric, and total VFA production in fecal samples. Four families belonging to the phylum Bacillota were influenced by dietary treatments with Erysipelotrichaceae and Clostridiaceae 1 being in higher abundance in LF diets and Ruminococcaceae and Lachnospiraceae being in higher abundance in HF diets. In conclusion, supplementation of BCVFA enhanced dietary fiber digestibility, particularly at the ileal level, which was associated with improved digestibility of other nutrients and can be potentially mediated by microbiome modulation.