Saccharomyces cerevisiae Supplementation in Canadian Finishing Feedlot Diets
Supplementation of Saccharomyces cerevisiae in the diet of cattle has been researched in dairy production systems; however, due to differences in experimental design animal responses are variable. Limited research exists examining live yeast supplementation in the diets of high-grain fed feedlot cattle, where basal diets also contain monensin. Therefore, a set of experiments (I, II, and III) were conducted with a basal diet containing monensin, with similar high-grain inclusion rates, grain source, and the same yeast product and dose, to determine the impacts of live S. cerevisiae on animal performance, diet digestibility, ruminal parameters, carcass characteristics, and response to ruminal acidosis challenge and recovery. The results of these experiments demonstrated that live yeast supplementation had no impact overall performance and carcass characteristics. Additionally, live yeast supplementation did not influence continuous ruminal pH parameters compared to feeding monensin alone throughout a feeding period, induced ruminal acidosis challenge or its subsequent recovery. Indifference in ruminal acidotic status between live yeast and control treatment groups resulted in similar immune marker concentrations and similarities in in vivo gut permeability measurements across all periods. In Experiment II, it was found that autolyzed yeast reduced ruminal pH during the feeding period, resulting in more time spent under acidotic thresholds compared to feeding monensin alone. In Experiment III, although differences were not observed between the yeast and control treatments, the ruminal acidosis induction was successful, with the recovery of ruminal pH between 2-4 days post-induction, dependent on the parameter examined. Surprisingly, ruminal acidosis induction reduced circulating SAA and LBP levels from baseline, which may indicate a chronic immune response to the high-grain diet that was not fully adapted. Additionally, post-ruminal gut permeability measurements indicated an improvement between 5-15 days post-induction, although not different from baseline indicating increased hindgut permeability despite insult by acidosis induction to the rumen. Overall, the addition of live S. cerevisiae to a high-grain feedlot diet containing monensin does not have differing effects on animal performance, diet digestibility, carcass characteristics, ruminal pH parameters or, response to ruminal acidosis challenge regarding ruminal pH, VFA, or gut permeability compared to feeding monensin alone.