343. Effects of Supplementation of an Active-dry Yeast Saccharomyces Cerevisiae CNCM I-1077 on Growth Performance of Moderate-risk Backgrounded Calves.

Abstract The objective of this trial was to evaluate the effect of supplementation of an active dry yeast on growth performance of moderate-risk calves during a 60-d backgrounding period. A total of 736 newly weaned, crossbred steers [initial body weight (IBW) = 295 ± 21.1 kg] were utilized with an average of 92 steers per pen and 4 replications per treatment. Steers were blocked by arrival date, fed a common ration of long-stem grass hay and a corn silage-based diet on arrival for 7 days to encourage intake. Steers were assigned randomly to treatment pens and fed from July 2024 through January 2025. The diet consisted of 32.6% dry rolled corn, 23.1% corn silage, 20.9% dried distillers grains plus solubles, 17.4% ground hay, and 6.0% liquid supplement which provided 15.12% CP, 22.12% starch, 20.88% ADF, and 35.31% aNDFom, 64.66% TDN (Table 1). Dietary treatments consisted of the inclusion of Saccharomyces cerevisiae CNCM I-1077 (SC-1077) at a feeding rate of 8 billion CFU/hd/d for the treatment group or control (CON), without SC-1077. The calculated SC-1077 amount was weighed out daily and incorporated into the feed truck at each morning’s feeding after CON calves had been fed. Measured parameters include IBW, ending body weight (EBW), total weight gain (TWG), dry matter intake (DMI), average daily gain (ADG), feed efficiency (G:F) and cost of gain (COG). Data were analyzed using linear mixed models in R (4.5.1), with treatment as a fixed effect and block as a random effect. Treatment differences were considered significant at P ≤ 0.05. No significant differences were observed in IBW, EBW, or TWG (P ≥ 0.17; Table 2). Although not significantly different, DMI for SC-1077 was numerically lower (P = 0.22) and ADG for SC-1077 was numerically greater (P = 0.19) than CON resulting in a significant (P = 0.04) improvement in feed efficiency. Steers fed SC-1077 were more efficient than steers that were fed CON which led to a $0.16 per steer per day improvement in COG (P = 0.04) and a return on investment of 6.6:1. In conclusion, supplementation of an active dry yeast in high-fiber backgrounding diets improved feed efficiency and reduced cost of gain in newly weaned beef calves. These performance benefits may be associated with improved rumen conditions favoring fiber-digesting microorganisms during the backgrounding period. For image description, please refer to the figure legend and surrounding text. For image description, please refer to the figure legend and surrounding text.