Use of a live yeast strain of Saccharomyces cerevisiae in a high-concentrate diet fed to finishing Charolais bulls: effects on growth, slaughter performance, behavior, and rumen environment

Aim of this study was to evaluate effects on growth, slaughter performance, behavior, and rumen environment parameters of dietary supplementation with a live yeast strain of Saccharomyces cerevisiae in a high-concentrate finishing diet fed to young Charolais bulls. A total 171 bulls (initial body weight (BW) = 442 +/- 22.8 kg) were stratified by BW and assigned to one of two experimental groups: Control (85 bulls) and Yeast (86 bulls). Each group was allotted to 6 contiguous pens. All bulls were fed the same finishing diet ad libitwn as a total mixed ration (TMR) at 0900 h. The live yeast strain of Saccharomyces cerevisiae CNCM 1-1077 was added to the Yeast bull premix to target a daily dose of 5 g/bull. Bull final BW (743 +/- 18.7 kg) and average daily gain (1.64 +/- 0.12 kg) did not differ between groups. However, yeast increased dry matter (DM) intake (11.0 versus 10.4 kg/d; P = 0.04) and tended to reduce (P = 0.08) the number of days required for finishing. The effect of yeast on DM intake was particularly relevant in the first weeks of fattening, possibly as a sign of better adaptation by bulls to the high-energy concentration of the finishing diet. Carcass weights and dressing did not differ between treatments, but the likelihood of producing a carcass graded as excellent by conformation score was 2.15 times higher for Yeast than Control bulls (Chi-Square = 14.7 and 95% confidence interval = 1.42-3.27; P < 0.001). Observation of bull behavior assessed during the 8 h after TMR delivery at the end of the 2nd and 4th mo of fattening showed a similar eating and ruminating pattern between treatments. However, yeast provision prevented from the drop in rumination rate (min/kg DM) recorded in Control bulls from the 2nd to the 4th mo of fattening. Physical and chemical analysis of TMR samples collected from the mangers at determined intervals after TMR delivery indicated that bulls of both treatments preferentially selected towards long fibrous particles. Rumen pH, lactic acid and total volatile fatty acid concentrations in samples collected before TMR feeding after the 3rd month of fattening were not affected by treatment but yeast increased acetate and butyrate concentrations as well as acetate:propionate ratio. Post mortem inspection of rumen wall showed that the occurrence of rumen papillae hyperkeratinization was lower for Yeast than Control bulls (relative risk = 0.51 and 95% confidence interval = 0.27-0.95; P = 0.02).