Effect of Original XPC in Receiving Diets on Newly Weaned Beef Steer Performance.

The objective of this study was to determine the effect of Original XPC, a Saccharomyces cerevisiae fermentation product (Diamond V, Cedar Rapids, Iowa) on growth performance and immune function of newly weaned beef cattle. One hundred eighty single-source newly weaned beef steers (278 ± 21.7 kg SD) were adapted for seven days, blocked by BW, and randomly assigned to treatments: Original XPC at 0 (CON), 14 (XPC14), or 28 g·steer·day^-1 (XPC28). Pen was the experimental unit (n = 10 per treatment, 6 steers per pen). Weights were collected on d -1, 0, 14, 28, 42, 55, and 56. Cattle were boostered against BVDV Type 1 and 2 (Vista Once, Merck, Madison, NJ) on d 0. One steer per pen was bled on d 0, 14, 28, 42, and 56 for analysis of antibody titers and blood from d 0, 28, and 56 was analyzed for red blood cell lysate superoxide dismutase (SOD) activity and glutathione concentration, plasma malondialdehyde (MDA) concentration, and serum lysozyme activity. Data were analyzed as a randomized complete block design using Proc Mixed of SAS; treatment and block were fixed effects. Performance and antibody titers were analyzed as repeated measures with the repeated effect of day; however, there were no treatment by day effects (P ≥ 0.41). Linear and quadratic contrast statements were constructed. There were no linear or quadratic effects of XPC on final BW, DMI, ADG, G:F, antibody titers, percentage of animals treated with antibiotics, or lysozyme activity (P ≥ 0.05). There was a quadratic effect of XPC on d 56 SOD activity (P = 0.004) driven by lesser activity in XPC14-fed steers. There was a tendency for a linear increase in MDA concentration on d 28 (P = 0.09). There was a quadratic effect of XPC on the d 28 oxidized to reduced glutathione ratio (P = 0.05), driven by a smaller ratio for XPC14. Greater reduced glutathione concentrations for XPC14 caused a tendency for a quadratic effect on d 28 and 56 (P = 0.09 and 0.07). A tendency for a linear increase in total glutathione concentrations in XPC-fed steers was noted on d 56 (P = 0.09). These results could indicate lesser levels of oxidative stress for animals receiving Original XPC at 14 g/d.