123 Effects of a <i>Saccharomyces cerevisiae</i> based direct-fed microbial on performance, health, and rumen bacterial community of newly weaned beef steers during a 56-d receiving period

Abstract We examined the effects of a blend of Saccharomyces cerevisiae, multiple live probiotic bacteria and their fermentation products on performance, health, and the ruminal bacterial community of newly weaned beef steers during a 56-d receiving period. Newly weaned Angus crossbred steers [n = 40; 221 ± 25.6 kg body weight (BW); 180 ± 17 d of age] were stratified by BW into four pens (10 steers per pen) such that each pen had a similar average BW at the beginning of the experiment. The pens were randomly assigned to receive a corn silage basal diet (CON; n = 20) or the basal diet supplemented with 9 g·steer⁻¹·d⁻¹of PRO feed additive (PRO; n = 20). The PRO additive is a blend of Saccharomyces cerevisiae and the fermentation products of Enterococcus faecium, Bacillus licheniformis, Bacillus subtilis, Lactobacillus animalis, Propionibacterium freudenreichii. The DMI and water consumed were monitored using the GrowSafe intake nodes and custom flow meters, respectively. Body weights were recorded weekly to calculate average daily gain (ADG). Before morning feeding, 10 mL of blood was taken from each steer on d 0 to 7, and thereafter weekly for analyses of immune cells, plasma glucose and NEFAs. On d 56, rumen fluid samples (200 mL each) were collected from all the steers for microbiome analysis. Over the 56-d receiving period, the supplemental PRO had no effects on DMI, water intake, or ADG. However, compared with CON, beef steers fed supplemental PRO tended to have greater ADG (P = 0.08) and BW (P = 0.07) during the first 14 d of the study. There was a treatment × day interaction (P ≤ 0.05) for WBC, neutrophils and monocytes over the 56 d such that beef steers fed supplemental PRO had decreased blood concentrations on certain days during the first 7 d after weaning, indicating reduced inflammation or stress response. The results of the rumen microbiome analysis revealed that the relative abundance of complex fiber degrading or obligate proton-reducing bacterial genera such as Bacteroides, Ruminococcus gauvreauii group, Desulfovibrio, Syntrophococcus, and Acetitomaculum were greater (P ≤ 0.05) in beef steers fed supplemental PRO compared with CON. This study demonstrated that dietary supplementation of PRO improved the growth performance, reduced stress or inflammatory response during the initial days after weaning and altered the ruminal bacterial community towards increased relative abundance of bacterial genera associated with improved rumen function.