PSIII-25 Whole blood RNA-Seq analysis reveals the immunomodulatory effects of a supplemental multi-strain direct-fed microbial in the diet of newly weaned beef steers.

Abstract We examined the effects of a blend of live Saccharomyces cerevisiae, multiple live probiotic bacteria, and their fermentation products on the whole blood transcriptome of newly weaned beef steers during a 56-d receiving period. Forty newly weaned Angus crossbred steers (12-h postweaning; 217 ± 4.6 kg of body weight [BW]; 202 ± 4 d of age) from three sources were stratified by BW and randomly assigned to one of the two treatments: 1. basal diet with no additive (CON; n = 20), and 2. the basal diet supplemented with 9 g/steer/d of a multi-strain microbial additive (PRO; n = 20). The PRO additive is a blend of S. cerevisiae and the fermentation products of Enterococcus faecium, Bacillus licheniformis, B. subtilis, Lactobacillus animalis, and Propionibacterium freudenreichii. On day 56, 10 mL of blood was collected from 10 randomly selected beef steers from each treatment group prior to morning feeding (after overnight feed withdrawal). Total RNA was isolated from the whole blood samples, and gene expression profiles of the beef steers fed PRO and CON were analyzed and compared. Differentially expressed genes (DEGs) were determined using FDR ≤ 0.10. A total of 40 DEGs was identified; the expression of 21 genes, such as TLR10, GPR183, LGR4, FCRL1, HHEX, TRAF5, and HLTF, were upregulated in beef steers fed the PRO diet compared to CON, whereas the expression of 19 genes, including C3, DDIT4, MEGF11, STAB1, and ADCY8 were downregulated. Gene ontology analysis of the DEGs revealed the enrichment (FDR< 0.05) of biological processes related to positive regulation of inflammatory response, regulation of cytokine secretion, positive regulation of defense response, and response to external biotic stimuli in beef steers fed PRO feed additive. In conclusion, this study revealed that beef steers fed PRO exhibited increased mRNA expression of genes related to immune function and inflammatory response, suggesting that the PRO additive may help modulate immune competence and enhance resilience to stress during the weaning and receiving period. These findings highlight the potential of multi-strain direct-fed microbials as a nutritional intervention to improve health outcomes in newly weaned beef steers.