Rhodotorula mucilaginosa ZTHY2 as a promising antibiotic alternative in Leizhou black ducks: impact on growth, meat quality, intestinal health, and microbiota composition.

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 × 107, 2 × 108, or 2 × 109 CFU/kg ZTHY2. The LA group was fed a diet supplemented with 2 × 109 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 × 108 CFU/kg and 2 × 109 CFU/kg, with P < 0.05. Notably, 2 × 109 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 pH24h value (P < 0.05). The crude protein content of the pectoral muscle was significantly greater (P < 0.05) in the 2 × 109 CFU/kg RM and 2 × 109 CFU/kg LA groups, whereas the crude fat content was lower in the 2 × 107 CFU/kg, 2 × 109 CFU/kg RM, and 2 × 109 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 × 109 CFU/kg ZTHY2. This study provided a theoretical basis for incorporating Rhodotorula mucilaginosa ZTHY2 into nonmedicated poultry feed formulations.