The Effects of a Protected Yeast Probiotic (Saccharomyces cerevisiae) on the Performance and Gut Microbiome of Ross 708 Broilers Grown to 49 Days of Age

This study evaluated increasing dietary doses of a live yeast probiotic (Saccharomyces cerevisiae) on broiler growth performance and cecal microbiota. A total of 1200 day-old straight-run Ross 708 chicks were allocated to five treatments (12 replicate pens/treatment; 20 birds/pen): a diet with 5% dried distillers grains with solubles and no gut-health additives (negative control, NC); NC plus bacitracin methylene disalicylate at 55 mg bacitracin activity/kg (positive control, PC); and NC plus live yeast at 0.25, 0.375, or 0.50 g/kg (LY1–LY3). Body weight (BW), feed intake, and mortality-corrected feed conversion ratio (FCR) were measured from d 1 to 49, and cecal microbiota were profiled by 16S rRNA gene sequencing on d 49. All yeast doses reduced cumulative FCR from d 1 to 35 compared with NC (p < 0.001). LY2 and LY3 also reduced cumulative FCR to d 42, but only LY3 reduced FCR over d 1–49 (1.733 vs. 1.774; p = 0.035), and FCR did not differ among yeast doses. LY2 and LY3 increased BW at d 42 (p = 0.04), but BW did not differ at d 49 (p = 0.77). In cecal samples from three birds per pen, analyzed with pen as the experimental unit, live yeast was associated with greater alpha diversity and differences in community composition, with no difference in within-group dispersion among treatments. Live yeast improved cumulative feed efficiency without a lasting effect on final BW.