Effects of a Saccharomyces cerevisiae fermentation product in receiving diets of newly weaned beef steers I: Growth performance and antioxidant defense.

To evaluate the effects of a Saccharomyces cerevisiae fermentation product (SCFP; Original XPC, Diamond V, Cedar Rapids, IA) on growth performance and antioxidant defense of newly weaned beef cattle, 180 single-source steers (278 ± 21 kg; SD) were used in a 56-d receiving study. Seven days after arrival, steers were blocked by body weight (BW) to pens of six and randomly assigned to treatments: SCFP at 0 (CON), 14 (SCFP14), or 28 (SCFP28) g·steer-1·d-1. Pen was the experimental unit (n = 10 per treatment). On d 0 steers were boostered against Bovine Viral Diarrhea Virus (BVDV) Type 1 and 2 (Vista Once, Merck, Madison, NJ). Weights were collected on d -1, 0, 14, 27, 42, 55, and 56. One steer per pen was bled on d 0, 14, 27, 42, and 56 for analysis of BVDV antibody titers; blood from d 0, 27, and 56 was analyzed for red blood cell lysate superoxide dismutase (SOD) activity and glutathione (total = tGSH, oxidized = GSSG, and reduced = GSH) concentrations, plasma malondialdehyde (MDA) concentrations, and serum lysozyme activity. Performance and blood data were analyzed as a randomized complete block design using Proc Mixed of SAS with fixed effects of treatment and block and random effect of pen. Linear and quadratic contrast statements were used. Antibody titers were log transformed and analyzed as repeated measures. There were no treatment by day interactions (P ≥ 0.16), and no linear or quadratic effects of SCFP on feedlot performance, antibody titers, or lysozyme activity (P > 0.10). Day 27 MDA concentrations tended to linearly increase (P = 0.09). A quadratic effect of SCFP on d 56 SOD activity (P = 0.004) was driven by lesser activity for SCFP14-fed steers. On d 27 a tendency for a quadratic effect of SCFP (P = 0.09) on GSH was driven by greater concentrations for SCFP14-fed steers resulting in a lesser GSSG:GSH ratio (P = 0.05). Greater GSH for SCFP14-fed steers caused a tendency for a quadratic effect on d 56 (P = 0.07); however, this did not result in an effect of SCFP on the GSSG:GSH ratio (P ≥ 0.25). A tendency for a linear effect of SCFP on tGSH was noted on d 56 (P = 0.09). Morbidity data were analyzed using Proc Glimmix of SAS. There was a quadratic effect of SCFP on percentage of respiratory treatments prior to d 14 (P = 0.04). These results could indicate lesser levels of oxidative stress for steers receiving SCFP at 14 g/d vs. 0 or 28 g/d. Under the conditions of this study no performance benefit of SCFP was noted.