Chromium propionate supplementation modulates rumen fermentation, immune response, temperament, and growth of recently weaned Brangus steers.

This experiment evaluated the effects of chromium (Cr) propionate supplementation on rumen fermentation, immune response, temperament, and growth of Brangus steers during preconditioning. Sixty Brangus steers (body weight [BW] = 250 ± 31.5 kg) were assigned to one of two treatments (six pastures per treatment; five steers/pasture): 1) Control (no Cr) or 2) Cr (0.01 mg of Cr/kg of BW). Chromium propionate was top-dressed onto soybean hulls, which were offered at 0.7% BW/day. Bermudagrass hay was provided ad libitum. Steers were vaccinated on d 0, and BW and blood samples were collected on d 0, 22, and 59, with rumen fluid collected on d 0 and 56. Liver Cr concentrations tended to be greater (P = 0.08) in Cr vs. Control steers. Rumen fluid concentrations of acetate and total volatile fatty acids (VFA) tended to be greater (P = 0.09), whereas molar proportions of isovalerate were less (P = 0.04), and isobutyrate and valerate tended to be less (P = 0.10) in Cr vs. Control steers. At the phylum level, the richness tended to be greater (P = 0.10) in Cr vs. Control steers. At the genus level, the abundance of Prevotella was less (P = 0.05), and Eubacterium, Roseburia and Anaerobutyricum tended to be greater (P ≤ 0.09) in Cr vs. Control steers. Serum insulin tended to be less (P = 0.08), and cortisol was less (P = 0.05) on d 22 in Cr vs. Control steers. Additionally, serum glucose tended to be less (P = 0.10), independent of day, in Cr vs. Control steers. Serum parainfluenza-3 (PI3) virus titer concentrations tended to be greater (P = 0.10), independent of day, in Cr vs. Control steers. Serum bovine viral diarrhea virus type 1 (BVDV-1) titer concentration was greater (P < 0.01) and bovine respiratory syncytial virus (BRSV) seroconversion tended to be greater (P = 0.09) on d 22 in Cr vs. Control steers. Additionally, the seroconversion for infectious bovine rhinotracheitis (IBR) tended to be greater (P = 0.09) on d 59 in Cr vs. Control steers. Exit scores from the squeeze chute were less (P = 0.04) on d 22 and 59, and the exit velocity tended to be less (P = 0.08) on d 22, in Cr vs. Control steers. Average daily gain was greater (P = 0.03) from d 0 to 22 but similar thereafter (P = 0.13) in Cr vs. Control steers. Thus, Cr supplementation shifted rumen fermentation toward greater fiber-derived VFA production, improved vaccine-induced immune responses, reduced stress, and enhanced early-phase growth during preconditioning.