Abstract
The potential of Rhodotorula yeast culture (RYC) in animal production remains underexplored. This study investigated the effects of RYC supplementation on nutrient apparent digestibility, rumen tissue morphology, fermentation parameters, and fungal microbiota in sheep. Twenty-four three-month-old male Dorper × Han crossbred sheep (weight 36 ± 4 kg) were selected and randomly divided into four groups, with six sheep in each group: the control group (CON) was fed a basal diet, and the three treatment groups were supplemented with 10, 20, or 40 g/d of RYC (RYC10, RYC20, RYC40), respectively. The results showed that RYC supplementation significantly increased (p < 0.05) the apparent digestibility of dry matter, crude protein, neutral detergent fiber, and acid detergent fiber, and the apparent digestibility of CP and ADF was significantly higher in the RYC20 than in the other groups (p < 0.05). Rumen papillae length and muscular layer thickness were significantly greater (p < 0.05) in RYC-treated groups compared to the CON group, and the RYC20 group exhibited significantly greater rumen papilla length and muscularis propria thickness than the other experimental groups (p < 0.05). Furthermore, ruminal pH and bacterial crude protein content were significantly elevated (p < 0.05), while ammonia nitrogen concentration was significantly reduced (p < 0.05). The RYC40 group exhibited significantly higher rumen pH and BCP concentrations, and significantly lower NH3-N concentration, compared to the other experimental groups (p < 0.05). The concentrations of acetate, propionate, butyrate, and total volatile fatty acids were also significantly higher (p < 0.05) in RYC groups. For RYC20, rumen acetic acid, propionic acid, butyric acid, isobutyric acid, total volatile fatty acid content and the acetate-to-propionate ratio were significantly higher than those of the other experimental groups (p < 0.05). Analysis of fungal community revealed that RYC increased the relative abundance of fibrolytic fungi (e.g., Neocallimastix, Caecomyce, Piromyces). Supplementation of RYC at 20 g/d optimizes apparent nutrient digestibility and rumen tissue development in ruminants, while maintaining favorable rumen fermentation characteristics and selectively enhancing the growth of core fibrolytic fungi; this dosage achieves the optimal balance of biological performance and economic feasibility, and is thus recommended as the optimal practical supplementation dosage for ruminant production.