Single or Combined Supplementation of Rhodotorula Yeast Culture and Bacillus Subtilis Enhances Intestinal Barrier...

This study aimed to investigate the effects of dietary supplementation with Rhodotorula yeast cultures (RYC) and Bacillus subtilis (BS), alone or in combination, on growth performance and intestinal barrier function in yellow-feathered broilers. A 2 × 2 factorial interaction study was conducted, in which a total of 192 one-day-old yellow-feathered broilers were randomly assigned into four treatment groups: CON group, fed a basal diet; BS group, supplemented with 5 × 10⁹ CFU/kg of BS; RYC group, supplemented with 5000 mg/kg of RYC; and RYC + BS group, supplemented with both. During the 56-day experimental period, body weight, average daily feed intake, average daily gain, and feed conversion ratio were not significantly affected by RYC, BS, or their interaction (p > 0.05). In the jejunum, the villus height-to-crypt depth ratio was significantly increased by the interaction of RYC and BS (p < 0.05). mRNA expression of tight junction proteins (JAM2, TJP1) was significantly upregulated by BS alone (p < 0.05), but this effect was diminished when RYC and BS were combined, indicating an antagonistic interaction between the two supplements. Mucin-2 (MUC2) expression was significantly increased by RYC or BS alone (p < 0.05). In immune function analysis, IgM levels were significantly increased by RYC alone but decreased when RYC and BS were combined (p < 0.05), further highlighting their antagonistic interaction. BS supplementation significantly increased IgG and pro-inflammatory gene expression (TNFA, IL1B, and NFKB1) (p < 0.05), while RYC supplementation reduced IFN-γ and increased anti-inflammatory gene expression (IL10 and MyD88). Cecal microbial analysis revealed increased abundance of g_Bacillus in the BS group, g_norank_f__norank_o__Clostridia_UCG-014 in the RYC group, and g_norank_f__norank_o__norank_c_Clostridia in the BS + RYC group were significantly increased compared to the CON group (p < 0.05). These results suggest that RYC and BS, as dietary supplements, may enhance intestinal health and barrier function in yellow-feathered broilers with minimal effects on growth performance. However, the antagonistic interactions between RYC and BS in modulating immune responses and tight junction protein expression highlight the need for careful consideration when combining these supplements in poultry nutrition strategies.