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Global attention to food safety and antimicrobial resistance issues continues to rise, and the need for green, efficient antibiotic alternatives in the livestock industry has become urgent. Prebiotics and probiotics, owing to their significant efficacy in regulating intestinal health and enhancing host immunity, are regarded as promising alternative approaches. Xylooligosaccharides (XOS), as a high-efficiency prebiotic, can specifically promote the metabolism and proliferation of beneficial bacteria such as Bifidobacterium. Based on this, this study uses Holstein calves as research subjects. It systematically investigates the effects of XOS and Bifidobacterium animalis (BA), used alone or in combination, on growth performance, immune-antioxidant function, rumen fermentation characteristics, and microbial composition. It aims to reveal the synergistic effects of the two and to provide a scientifically based, antibiotic-free nutritional strategy to promote healthy calf breeding. Thirty-two 2-month-old male calves were allocated to four dietary treatments (n = 8): (1) control diet (CON), (2) CON with 2 g/d XOS (XOS), (3) CON with 5 g/d BA (BA), and (4) CON with 2 g/d XOS with 5 g/d BA (XOS-BA). The 63-day trial consisted of a 7-day adaptation period followed by a 56-day sampling period. Daily feed intake was recorded. On day 63, jugular blood was collected for serum biochemistry, immune and antioxidant analyses, and rumen fluid was sampled for volatile fatty acids, 16S rRNA sequencing, and metabolomics analyses. The XOS-BA group increased final BW (P = 0.004) and average daily gain (P = 0.024), and decreased the feed-to-gain ratio (P = 0.002). Furthermore, XOS-BA supplementation positively affected the ruminal microbiota, increasing the abundances of beneficial taxa, including Acidobacteria, Lactobacillus, and Bifidobacterium. Further analyses revealed that XOS-BA effectively alleviated oxidative stress and inflammatory responses. This was evidenced by increased plasma immunoglobulin A and glutathione levels (P < 0.05) and decreased malondialdehyde concentrations. Meanwhile, compared with other treatments, the rumen fermentation function of calves supplemented with XOS-BA was significantly improved, as reflected by elevated rumen fluid acetic acid concentration (P = 0.036). In-depth analyses indicated that XOS-BA enhanced systemic antioxidant capacity by elevating endogenous antioxidant indices and reducing oxidative products, while modulating retinol metabolism, unsaturated fatty acid biosynthesis, and mTOR signalling. Synbiotic supplementation of XOS-BA synergistically improves growth performance, enhances immune-antioxidant capacity, and modulates rumen microbiota and metabolism in calves, thereby offering a practical antibiotic-free strategy for calf production.
Li et al. (Wed,) studied this question.