PSXV-11 - A Postbiotic from Saccharomyces Cerevisiae Fermentation Improves Microbiome Robustness in Young Stress-challenged Horses in Training

Abstract: Nutritional and environmental stressors can disturb the gut microbiome of horses which may ultimately decrease their health and performance. In this study, we hypothesized that a Saccharomyces cerevisiae fermentation postbiotic (SCFP) improves the robustness of the gut microbiome in stress-challenged horses. Quarter horses (n=20) were randomized based on sex, age (22 ± 3 mo) and body weight (439 ± 3 kg) to receive a basal diet (60% forage:40% concentrate) supplemented without (CON) or with SCFP (21g/d, TruEquine, Diamond V, Cedar Rapids, IA). Treatments were implemented for 60 d. On d 57, horses were tethered with their heads elevated 35 cm above wither height for 12 h to mimic long-distance transport stress. Fecal samples were collected on d 0, 28, and 56 pre-challenge and at 0, 12, 24 and 72 h post-challenge and subjected to DNA extraction and Nanopore shotgun metagenomics. Alpha-diversity and microbial abundances were compared using non-parametric Wilcoxon-Rank-Sum test with Benjamini-Hochberg FDR correction. The SCFP stabilized alpha-diversity across all time points, whereas CON horses had more fluctuation (P < 0.05) at 12, 24 and 72 h post-challenge compared to d 56. This resulted in a significant difference between CON and SCFP at 0 and 12 h. There was no difference in beta-diversity between SCFP and CON on d 56, however, treatments grouped separately (PERMANOVA, P < 0.05) within the 12 h post-challenge showing SCFP horses maintained higher abundances (P < 0.05) of fibrolytic taxa such as Fibrobacter succinogenes, Ruminococcus species and several members of Prevotellaceae and Lachnospiraceae among others. During the post-challenge period compositional clusters in the microbiome of CON horses were characterized by low abundances (P < 0.05) of Butyrivibrio, Pseudobutyrivibrio and Blautia species versus SCFP. Overall, treatments were similar in microbiome diversity and composition pre-challenge, however, post-challenge, SCFP supplementation improved microbiome robustness indicating an ability to resist change due to stress.