PSIX-11 - The Effect of Probiotic Supplementation on the Alpha Diversity and Proteobacteria Ratio in South African Feedlot Cattle in the Finisher Phase

Abstract: Probiotics are known to stabilize the microbiome especially in monogastric animals. Limited information is available on the potential effect on the rumen microbiome. Feedlot cattle are fed high concentrate diets which may result in subclinical and clinical acidosis due to dysbiosis. This can negatively affect the production and lead to morbidities and death. The alpha diversity of a microbiome population and the ratio of Proteobacteria towards Firmicutes and Bacteroidetes have been known to indicate potential dysbiosis. The aim of this study was to investigate the effect of probiotics on the alpha diversity and Proteobacteria ratio of the rumen microbiome of feedlot cattle during the finisher phase. Thirty-six Bonsmara bulls were randomly divided into three groups and fed for 120 days; a basal diet commonly fed in South African feedlots (CTR: control), the basal diet supplemented with monensin (30 mg/animal/day; MON) or a Bacillus-based probiotic (B. licheniformis and B. subtilis; Bovacillus, Chr. Hansen A/S at 2.75 g/animal/day; BOV). Four animals from each of the groups were randomly selected for rumen content collection during the finisher phase using a stomach tube. After DNA extraction was completed, 16S rRNA sequencing (V3-V4) was performed. Alpha diversity (Shannon) and the relative abundance of the phyla was determined using phyloseq with significance (p< 0.05) determined with the Kruskal-Wallis test. In total, 41 300 ASVs and 10 phyla were identified. BOV had a significantly greater (p=0.023) alpha diversity compared with CTR and numerically greater compared with MON. The Proteobacteria ratio was greater than expected in all groups. However, the ratio was significantly less in BOV compared with CTR (p=0.028) and numerically less compared with MON. The results indicate that probiotic supplementation of feedlot cattle has the potential to stabilize the rumen microbiome by increasing the alpha diversity and decreasing the Proteobacteria ratio thereby preventing dysbiosis.