Table 1_Effects of probiotic supplementation on growth and meat quality of Simmental bulls.xlsx

Probiotics are well established to enhance animal immunity and gastrointestinal health, while also improving meat tenderness and antioxidant status. This study evaluated the effects of dietary probiotic supplementation on growth and meat quality of Simmental bulls. Forty Simmental bulls were randomly assigned by body weight to one of four groups, receiving a basal diet supplemented with probiotics at 0, 0.1, 0.2, or 0.3 g per kg of dry matter (DM). The trial included a 20-day adaptation phase followed by a 60-day experimental period. Dietary probiotic supplementation did not affect DM intake or carcass traits (p > 0.05) but linearly increased average daily gain (p = 0.001) and reduced the feed conversion ratio (p = 0.001). Increasing the probiotic dose linearly enhanced meat redness (p = 0.007), while decreasing cooking loss (p = 0.022) and shear force (p = 0.014). Intramuscular fat content and triglyceride levels increased significantly (p = 0.017 and 0.001, respectively), showing linear and quadratic patterns. Antioxidant indices were also strengthened with increasing dosage, including total antioxidant capacity (p = 0.005) and glutathione peroxidase activity (p = 0.012) in a linear manner, and catalase activity (p = 0.012) in a quadratic manner. The probiotic supplementation linearly reduced the proportions of C16:0 (p = 0.008) and saturated fatty acids (SFA) (p = 0.001), and increased the proportions of C18:1n9c (p = 0.013), C22:5n3 (p = 0.017), monounsaturated fatty acids (p = 0.009), polyunsaturated fatty acids (p = 0.007), unsaturated fatty acids (UFA) (p = 0.001), and the UFA/SFA ratio (p = 0.001). The probiotics linearly upregulated the mRNA expression of fatty acid synthase, acetyl-CoA carboxylase, and sterol regulatory element binding transcription factor 1 (p = 0.002, 0.001, and 0.010), quadratically upregulated stearoyl-CoA desaturase 1 and peroxisome proliferate-activated receptor α (p = 0.001 and 0.003), and linearly downregulated carnitine palmitoyltransferase 1B (p = 0.009). Collectively, our results establish that 0.2 g/kg DM is the optimal dosage of dietary probiotic supplementation for simultaneously enhancing bull growth and beef quality. This work validates probiotics as a sustainable feeding strategy and opens new avenues for improving meat quality through microbial manipulation.