Influence of dietary Saccharomyces cerevisiae on rumen fermentation characteristics, nutrient digestibility, and growth performance of Farafra lambs under desert conditions

This study investigated the effects of Saccharomyces cerevisiae supplementation on nutrient digestibility, rumen fermentation, blood metabolites, and growth performance of Farafra lambs under desert conditions. Eighteen lambs (5–6 months old, 26.5 ± 1.83 kg) were randomly assigned to three groups: control (basal diet), 1 g/day of yeast, and 1.5 g/day of yeast. The lambs were fed for 120 days under high ambient temperatures (maximum 39.5 ± 1.8 °C, THI 77–84.7). Supplementation with S. cerevisiae at 1.5 g/day significantly increased nutrient digestibility: dry matter (5.2%, P = 0.032), organic matter (4.1%, P = 0.041), crude protein (4.2%, P = 0.038), and neutral detergent fiber (8.2%, P = 0.029) compared with the control. Blood serum albumin increased by 5.8% ( P = 0.040), while cholesterol decreased by 12.7% ( P = 0.011) at the highest yeast level. Rumen total volatile fatty acid (VFA) concentration at 2 h post-feeding increased by 13.7% ( P = 0.021), with linear increases in acetate ( P = 0.045) and propionate ( P = 0.038). Rumen pH and VFA molar proportions remained within normal physiological ranges. Growth performance improved significantly: final body weight in the 1.5 g/day group reached 44.5 kg (13.8% vs. control, P = 0.037), total weight gain increased by 47.6% ( P = 0.035), and average daily gain improved by 47.5% ( P = 0.036). Feed conversion ratio improved by 28.1% ( P = 0.038), while feed intake remained unchanged. These results indicate that yeast supplementation improved nutrient utilization efficiency rather than stimulating feed intake. In conclusion, dietary supplementation with S. cerevisiae , particularly at 1.5 g/day, significantly improved digestibility, rumen fermentation, and growth performance of Farafra lambs under harsh desert conditions, providing a practical nutritional strategy to enhance lamb productivity in arid and semi-arid production systems.