PSI-27 Effects of Bioflavex Supplementation compared to monensin on rumen and gut microbiome composition in finishing steers.

Abstract Monensin, an ionophore antibiotic, is widely used in high-starch diets to prevent ruminal dysbiosis and improve feed efficiency. However, increasing restrictions on antibiotic feed additives have led to the exploration of alternatives such as Bioflavex, a natural citrus extract rich in flavonoids. Flavonoids have antioxidant, antimicrobial, and anti-inflammatory properties, making them a potential substitute for ionophores. This study aimed to compare the effects of Bioflavex and monensin supplementation on the rumen and hindgut microbiome of finishing steers, focusing on microbial diversity and taxonomic shifts. Forty-eight finishing steers (214.3 ± 50.99 kg LW) were assigned to either a Bioflavex (BF, 400 g/t DM) or monensin (M, 30 g/tn DM) diet. Rumen and fecal samples were collected at day 0, 21, and 86, with microbial DNA extracted and analyzed via 16S rRNA sequencing (DADA2 pipeline). Alpha and beta diversity indices, taxonomic composition, and differential abundances were assessed. Performance variables such as live weight, dry matter intake (DMI), and feed conversion efficiency (FCE) were recorded. Data were analyzed using a mixed-effects model, with treatment and time as fixed effects and pen as a random effect (P < 0.05 for significance, 0.05 < P < 0.10 for trends). At day 86, gut microbiome composition differed significantly, with Bioflavex-fed steers showing higher relative abundance (RA) of Gammaproteobacteria (P = 0.021) and lower Spirochaetia (P = 0.034), while monensin-fed steers retained a higher RA of Spirochaetota. Similarly, Bioflavex increased Bacteroidia RA in both the rumen (P = 0.049) and gut (P = 0.031), whereas monensin-fed animals maintained higher Clostridia RA (P = 0.027). At the genus level, Prevotella spp. was more abundant in the rumen of Bioflavex-fed steers (P = 0.045), while UCG-005 (P = 0.038) and Ruminobacter (P = 0.029) increased in the hindgut. These shifts suggest alterations in fermentation pathways, likely impacting volatile fatty acid (VFA) production and host-microbiota interactions. Performance was similar between treatments (P > 0.05), although a lower DMI (P = 0.009) was found in monensin treatment. Bioflavex-fed steers exhibited higher microbial diversity, which may improve gut stability and resilience. This diversity has been linked to reduced inflammation and better intestinal health in previous studies. In conclusion, Bioflavex supplementation induced significant microbiome modifications, particularly in the gut, where bacterial shifts may provide metabolic health benefits. While monensin improved short-term feed efficiency, Bioflavex promoted higher microbial diversity, potentially reducing intestinal inflammation. Further research is required to assess whether Bioflavex can fully replace monensin while providing metabolic and gut health advantages.