PS13-10. Effects of 14-day Post-Weaning Supplementation of a Saccharomyces Cerevisiae-Based Additive on Growth Performance and Immune Status of Beef Steers During a 112-D Backgrounding Period.

Abstract

The objective of this study was to evaluate the effects of 14-day post-weaning supplementation of a multi-species direct-fed microbial (DFM) blend on growth performance and circulating immune cell profiles of newly weaned beef steers over a 112-d backgrounding period. Forty newly weaned Angus crossbred beef steers (3-h post-weaning; 217 ± 2.3 kg BW; 202 ± 2 d of age) were stratified by BW and randomly assigned to 8 pens (5 steers/pen; 4 pens/treatment). Treatments were: a corn silage-based total mixed ration with no additive (CON; n = 4 pens) or the same diet supplemented with 9 g/head/d of the PRO additive (T14; n = 4 pens) for d 1–14 only, after which both groups received the unsupplemented basal diet through d 112. The PRO additive (Papillon, Easton, MD) contained live S. cerevisiae (1.41 × 109 CFU/g), Enterococcus faecium, Bacillus licheniformis, Bacillus subtilis, Lactobacillus animalis, Propionibacterium freudenreichii, and their fermentation products. Individual DMI was recorded continuously using GrowSafe nodes; BW was measured on d 1, 14, then biweekly through d 112. Blood was collected biweekly through d 56 and on d 112 for analysis of WBC, neutrophils, lymphocytes, and monocytes; the neutrophil-to-lymphocyte (N:L) ratio was computed as a stress indicator. Data were analyzed using the MIXED procedure of SAS with pen as the experimental unit; significance was declared at P ≤ 0.05. During d 1–14, T14 steers had greater DMI (5.34 vs. 4.53 kg/d; P = 0.0004) and tended toward greater ADG (1.28 vs. 1.05 kg/d; P = 0.07) compared with CON; feed-to-gain ratio (F:G) was unaffected (P = 0.41). These benefits persisted over the full 112-d study: T14 steers had greater overall ADG (1.86 vs. 1.71 kg/d; P = 0.03) and DMI (7.29 vs. 6.52 kg/d; P < 0.0001), despite supplementation ending at d 14. Final BW and F:G at d 112 did not differ between treatments (P ≥ 0.87). No treatment × day interactions were detected for any circulating immune cell population (P ≥ 0.29); however, T14 steers had a lower N:L ratio at specific sampling days (P = 0.02; SEM = 0.05), indicating transient attenuation of weaning-associated systemic stress. In conclusion, 14 days of post-weaning DFM supplementation improved early DMI and ADG, with carry-over benefits in ADG and DMI persisting over 112 days. A transient reduction in N:L ratio suggests short-term modulation of the weaning stress immune response. These findings support the strategic, short-term use of DFMs at weaning as a cost-effective tool to promote early adaptation and long-term performance in beef receiving or backgrounding programs.