Dose Titration of Plant-Based Flavonoid Blend Supplementation on Performance, Digestibility, Gut Microbiome, Blood Biomarkers, and Meat Quality of Growing Rabbits.

Rabbit meat is increasingly valued for its high nutritional quality, driving growing interest in enhancing its production through phytobiotics like plant-based flavonoid blend (PFB). So, this study looked at how a PFB at different doses influences the performance, digestibility, gut microbiota, blood biomarkers, liver health, and meat quality of growing rabbits. Sixty rabbits (body weight 552.63 ± 13.44 g) were assigned at random to five dietary groups, having twelve replicates per group. The rabbits were fed a basal diet as a total mixed ration having 17.02% crude protein and 11.60 MJ metabolizable energy/kg dry matter (DM), supplemented with PFB (g/kg diet) at 0.0 (control), 0.20, 0.40, 0.60, and 0.80. Following a 2 weeks adjustment period, the feeding trial was conducted for 5 weeks. When the trial was over, rabbits were sacrificed to collect digesta, blood, and meat samples for further analysis. Supplementation with PFB at 0.60 g/kg diet (range: 0.50-0.70 g/kg) showed a better final body weight (p = 0.01), weight gain (p < 0.001), and feed conversion ratio (p < 0.001), while significantly improving DM, nitrogen-free extract (p < 0.001), and ether extract (p = 0.02) digestibility. Besides, supplementation with PFB presented a linear reduction in Escherichia coli (p = 0.003), accompanied by linear improvement in Lactobacillus spp. (p < 0.001) and serum high density lipoprotein-cholesterol (HDL-C; p = 0.001). Broken-line analysis indicated optimal PFB supplementation levels of 0.60, 0.47, and 0.60 g/kg diet for E. coli, Lactobacillus spp., and HDL-C, respectively. However, feed intake, serum triglycerides, other cholesterols, total protein, albumin, globulin, and uric acid remained unchanged across the groups. Furthermore, supplementation with PFB with an estimated breakpoint of 0.55 g PFB/kg of diet effectively (p ≤ 0.02) reduced serum liver enzymes (aspartate aminotransferase, alanine aminotransferase, and alkaline phosphatase) indicating better liver health. In addition, PFB supplementation linearly reduced meat ether extract content and improved meat redness (p < 0.001), with optimal responses at 0.58 and 0.60 g/kg diet, respectively, while having no impacts on meat protein, ash, lightness, or yellowness. Therefore, dietary inclusion of PFB at 0.55 g-0.60 g per kg diet optimized growth performance through enhanced weight gain, feed efficiency, and nutrient digestibility, while favorably modulating cecum microbiome, serum cholesterol, liver enzyme activities, and ameliorated meat quality.