Abstract
Rhodotorula mucilaginosa ZTHY2 is safe, and can produce abundant nutrient metabolites, supporting the “no-resistance” culture as an additive in animal feed. In this study, the Leizhou black duck was chosen as the model organism to investigate the effects of ZTHY2 on animal growth, meat quality, intestinal health, and the gut microbiota composition. A total of 150 healthy, 1-day-old male ducks were randomly divided into five groups with 3 replicates each, with 10 birds per replicate. The control group was fed a standard diet, whereas the RM group received a diet supplemented with 2 × 10(7), 2 × 10(8), or 2 × 10(9) CFU/kg ZTHY2. The LA group was fed a diet supplemented with 2 × 10(9) CFU/kg Lactobacillus acidophilus. The experiment lasted 42 days. The analysis revealed significant improvements in the average daily gain for both the RM and LA groups over the control, with P < 0.05. The feed conversion ratios also significantly decreased at RM dosages of 2 × 10(8) CFU/kg and 2 × 10(9) CFU/kg, with P < 0.05. Notably, 2 × 10(9) CFU/kg RM improved the carcass yield percentage, reduced muscle water loss, and significantly altered the meat color L* and b* values in the ducks (P < 0.05). Additionally, it increased the a* value of pectoral muscles and the pH(24h) value (P < 0.05). The crude protein content of the pectoral muscle was significantly greater (P < 0.05) in the 2 × 10(9) CFU/kg RM and 2 × 10(9) CFU/kg LA groups, whereas the crude fat content was lower in the 2 × 10(7) CFU/kg, 2 × 10(9) CFU/kg RM, and 2 × 10(9) CFU/kg LA groups (P < 0.05) relative to the control. ZTHY2 administration significantly modified the amino acid and fatty acid profiles in duck muscles, increasing the contents of threonine and tyrosine and decreasing the proportion of nervonic acid (P < 0.05). ZTHY2 significantly increased the villus height and reduced crypt depth across all intestinal segments (P < 0.05), indicating improved morphology and architectural integrity. Additionally, ZTHY2 stabilized the intestinal microbiota, significantly improved the composition and structure of the gut floral community. In summary, the results suggested that ZTHY2 could improve the growth performance and muscle texture of the ducks by regulating intestinal microflora, promote intestinal health, and enhance growth and muscle quality. The most notable improvements were observed at 2 × 10(9) CFU/kg ZTHY2. This study provided a theoretical basis for incorporating Rhodotorula mucilaginosa ZTHY2 into nonmedicated poultry feed formulations. SUPPLEMENTARY INFORMATION: The online version contains supplementary material available at 10.1186/s12917-026-05292-3.