Thesis

Saccharomyces cerevisiae fermentation product (SCFP) has been shown to stabilize gut health and lactation performance in dairy cows, but its effects on pre-weaning calves remain inconclusive. This study evaluated the effects of a commercial SCFP on the physiological responses, growth performance, and the fecal microbiome of calves during weaning. Twenty-eight female Holstein calves (30–75 days of age) were randomly assigned to either control group (CON) or a treatment group (YC; 20 g/day SCFP), with complete weaning occurring at 60 days of age. SCFP supplementation significantly altered serum cortisol concentrations and the fecal microbiome, whereas other physiological parameters remained unaffected. Solid feed and water intake increased significantly post-weaning (p < 0.05). Although average daily gain (ADG) did not differ significantly between groups, the YC group exhibited a less pronounced post-weaning decline in ADG (CON: -0.16 kg/ YC: -0.07 kg). Changes in serum cortisol concentrations around weaning differed significantly between groups (p < 0.05), decreasing in YC calves (66.35 to 59.02 ng/mL) but increasing in CON calves (53.10 to 65.74 ng/mL). LEfSe analysis revealed that YC calves had a higher abundance of fibrolytic bacteria, including Ruminococcaceae, Oscillospiraceae, and Faecalibacterium. Although fluctuations in ambient temperature may have confounded diarrhea incidence, SCFP supplementation appeared to mitigated weaning stress by reducing cortisol secretion and enriching beneficial fibrolytic bacteria, potentially enhancing digestion and stabilizing body weight gain. Future studies should evaluate higher dosages, extend the observation period, and incorporate metabolomic analyses to elucidate the underlying mechanisms.

Key words: Saccharomyces cerevisiae fermentation product, calves, fecal microbiome