Influence of Saccharomyces cerevisiae CNCM I-1077 on the fecal pH, markers of gut permeability, fecal microbiota, and markers of systemic inflammation in sedentary horses fed a high-starch diet

Thirty mature Quarter Horse geldings were used in a completely randomized 32-d study to test the hypotheses that supplemental live Saccharomyces cerevisiae CNCM I-1077 improves apparent digestion, stabilizes the fecal pH, reduces gut permeability, maintains microbial communities, and decreases inflammation in horses fed a high-starch diet. Horses were stratified by body weight, age, and body condition score (BCS) to one of two treatments: concentrate formulated with 2g starch • kg BW-1 • meal-1 (CON; n=15) or the same concentrate top-dressed with 25g/d Saccharomyces cerevisiae CNCM I-1077 (SC; n=15; 8×108 CFU). Horses were fed individually in stalls every 12h. Between meals, horses were housed in dry lots with ad libitum access to water and Coastal bermudagrass hay. On d0 and 32, BW and BCS were recorded, and blood was collected before feeding and 2, 8, 16, and 24 h postmeal on d32 to analyze serum D-lactate. Fecal samples were collected on d0, 16, and 32 at 8, 16, and 24h post-meal for fecal pH and starch content. Intake and fecal production were recorded over 4-d to measure digestibility on d28-31. Whole blood total bacterial counts and 16S fecal microbiota rRNA sequencing were performed at d0, 16, and 32. Results revealed an increased ∆BW in SC horses compared with CON horses (P=0.03), with no change in BCS (P=0.97). D-lactate tended to be greater in SC horses on d32 at 16 and 24h post-meal compared with CON horses (P=0.10). Concentrations of TNFα and LogCCL2 decreased from d0 to d 32 regardless of dietary supplementation (P≤0.02). Fold change of percent reads from d0 in whole blood bacterial 16S rRNA did not differ between groups. Fecal starch was undetectable, and there were no differences in intake or apparent digestibility. Fecal pH tended (P=0.07) to be lower in CON at 0h on d32 (6.03 ± 0.06) than d16 (6.14 ± 0.06). Additionally, pH tended (P=0.09) to be lower in CON (6.03 ± 0.06) than SC (6.16 ± 0.06) at 0h on d32. Supplementation of Saccharomyces cerevisiae CNCM I-1077 maintained Bacteroidales and reduced acidosis-like bacteria like Streptococcus and potential pathogens like Enterobacteriaceae, Stenotrophomonas, and Rhodococcus at d16 (P<0.05). Further, supplementation increased fibrolytic bacteria at d32, such as Ruminococcus, Fibrobacter, and Succinivibrio (P<0.05). These results indicate Saccharomyces cerevisiae CNCM I-1077 increases BW and promotes a more diverse microbiome when hoses are fed ad libitum hay and a high-starch concentrate.