Targeted ileal microbiome modulation by in ovo seaweed polyphenols (Fucus spiralis) as an alternative to in-feed antibiotics in broiler chickens

Managing gut health is a priority for the poultry industry, and nutritional provision during early life may facilitate positive, lasting modulation of the gut microbiome. This study evaluated the effects of in ovo seaweed (Fucus spiralis) and green tea (Camellia sinensis) polyphenols on the ileal and cecal microbiome of broiler chickens using 16S rRNA amplicon sequencing. On embryonic day 17.5, viable embryos received one of four treatments via the amniotic route (50 µL): (1) standard control (no injection), (2) diluent control, (3) seaweed polyphenols (2.5 mg/egg), or (4) tea polyphenols (2.5 mg/egg). Following hatch, the 28-day grow-out trial proceeded as a 5 × 2 factorial arrangement (in ovo supplementation × dietary challenge). The in ovo supplementation factor comprised the initial four treatments plus (5) antibiotic control, derived from a subset of the no-injection control provided in-feed antibiotics (BMD® 110G). Each in ovo supplementation treatment was assigned to either a standard diet with unoxidized oil or the same diet containing oxidized oil, serving as a model for stress. Seaweed polyphenols suppressed Clostridium sensu stricto 1 (P < 0.05), a genus associated with necrotic enteritis in the ileum of 28-day-old birds, without altering dominant microbial taxa. This effect was comparable to what was achieved by 28 days of in-feed antibiotics (P > 0.05). The same effect was not observed with tea polyphenols. In the ceca, only the antibiotic control significantly altered the microbial composition compared to the standard control group, while neither polyphenols had a significant impact. The oxidized oil had minimal impact on both the ileal and cecal microbiome. Hatchability and growth performance (weight gain, feed intake, and feed conversion ratio) were not impacted by treatments (P > 0.05). Our findings suggest that a single dose of seaweed polyphenols supplemented in ovo is a viable alternative to the prolonged use of in-feed antibiotics for suppressing necrotic enteritis-associated microbes. This highlights early life as a critical window for nutritional provision to manage poultry gut health.