Saccharomyces cerevisiae Supplementation Improves Growth Performance and Heat Stress Tolerance in Angus Steers

Saccharomyces cerevisiae (SC) can be incorporated into ruminant diets as a postbiotic product. This study aimed to explore the effects of supplementing different levels of SC in the diets of mid-fattening Angus steers under heat stress conditions. A total of twenty-seven steers were randomly allocated into 3 groups: control, 30 g SC addition and 60 g SC addition groups. After a 7-day adaptation period followed by a 120-day experimental period, including respiratory rate, rectal temperature, growth performance, apparent digestibility of nutrients, rumen fermentation parameters, urine metabolites, serum biochemistry and antioxidant were measured. The results showed that the rectal temperature and respiratory rate of cattle decreased upon the addition of SC during heat stress. Meanwhile, the growth performance of cattle was improved in the 30 g SC addition group. The serum energy metabolism related indexes, such as non-esterified fatty acids, glucose, and β-hydroxybutyric acid, were altered. Additionally, the activity of catalase was significantly enhanced with the addition of SC. Overall, the addition of SC to the diets of mid-fattening Angus steer did not negatively affect rumen fermentation and nutrient apparent digestibility. Instead, it was capable of improving physiological performance under heat stress by modifying the energy metabolism and augmenting antioxidant capacity, which ultimately led to an improvement in growth performance. In conclusion, the most suitable level of SC to be added to the diet of mid-fattening Angus steers is 30 g/steer/d.