Abstract
This study aimed to assess the impact of Saccharomyces cerevisiae fermentation product (SCFP) on digestibility, ruminal fermentation, and plasma metabolome of Holstein steers fed a high-grain diet. Steers were fed diet with 80% concentrate and 20% corn silage once daily ad libitum. Steers were stratified based on initial body weight (BW) and randomly assigned to two treatments: 1) control (CON), a basal diet without SCFP; 2) basal diet + 12 g/head/day SCFP, top-dressed. Eight rumen-cannulated Holstein steers (BW: 580 ± 29.2 kg) were enrolled in a crossover design study with 25-d treatment periods and a 24-d washout period. Dry matter intake (DMI) was calculated from daily feed offered and refusals. Blood was collected before morning feeding on day 25 of each period. Rumen fluid was collected at 0, 4, 8 and 12 h post-feeding on d 25. Fecal samples were collected from d 22 to 24 for digestibility measures. Statistical analyses were performed with the GLIMMIX procedure of SAS 9.4 (SAS, 2023). Supplementing SCFP had no effect on digestibility of organic matter (OM, P = 0.63), crude protein (CP, P = 0.97), neutral detergent fiber (NDF, P = 0.59), and acid detergent fiber (ADF, P = 0.84). Treatment did not affect fecal excretion of nitrogen (N, P = 0.69), phosphorus (P, P = 0.24), copper (Cu, P = 0.71), and zinc (Zn, P = 0.95). Supplementing SCFP increased (6.29 vs. 6.01, P = 0.01) ruminal pH compared to CON. Lactic acid concentrations were similar between treatments (P = 0.17) and low in both groups (0.09mM vs. 0.28mM). Treatment did not affect ruminal total volatile fatty acid (VFA) concentrations (P > 0.10) but decreased butyrate molar proportion (P = 0.01) and tended to increase the molar proportions of isobutyrate (P = 0.06) and isovalerate (P ≤ 0.10). Treatment had no effect on the in vitro production of proinflammatory cytokines, IL-1β (P > 0.11) and IL-6 (P > 0.12), in the whole blood in response to various toll-like receptor stimulants. Plasma pathways of purine metabolism, amino sugar and nucleotide sugar metabolism, and lysine degradation were enriched (P ≤ 0.05) by feeding SCFP. Overall, supplementing SCFP did not affect total tract digestibility, fecal excretions of macro minerals but enhanced ruminal pH in cattle fed a high-grain diet. Furthermore, feeding SCFP enriched several important plasma pathways related to protein metabolism.