Dietary sublancin or oregano essential oil enhances growth and immunity in goat kids via modulating colonic microbiota and bile acids.

The gut microbiota-bile acid (BA)-immune network is critical for ruminant health. This study investigated the effects of dietary sublancin or oregano essential oil (OEO) on growth performance, immunity, colonic microbiota, and BA metabolism in fattening goat kids. Twenty-four 3-month-old Saanen goat kids (16.08 ± 1.29 kg) were randomly assigned to four groups (n = 6): control (C), OEO (O; 7 g/d), sublancin (S; 2 g/d), and half-dose combination (M; 3.5 g/d OEO + 1 g/d sublancin). The 139-d trial showed that, compared with the C group, OEO supplementation enriched colonic Bacteroidota phylum and Muribaculaceae family, and increased anti-inflammatory secondary bile acids (SBAs) and tauro-beta-muricholic acid, elevated serum immunoglobulin (Ig) G and IgA levels (P < 0.05), decreased pro-inflammatory cytokines and malondialdehyde (MDA) level, and increased average daily gain (ADG) (P < 0.05). Sublancin enriched Firmicutes and Christensenellaceae_R-7_group, increased anti-inflammatory SBAs (especially taurohyodeoxycholic acid), elevated IgA, IgG, complement 3, and complement 4 levels (P < 0.05), suppressed interleukin (IL)-1β, IL-6, and tumor necrosis factor (TNF)-α concentrations (P < 0.001), increased catalase (CAT) activity and decreased MDA level (P < 0.05), and improved ADG and feed-to-gain ratio (F/G) (P < 0.05). Despite exhibiting the optimal growth performance, the M group displayed Bacteroidota enrichment, decreased most BAs but increased oxidized BAs mainly including 12-dehydrocholic acid and 7-ketodeoxycholic acid concentrations (P < 0.01), with preserved anti-inflammatory effects but limited immune enhancement. Taurohyodeoxycholic acid was positively correlated with Christensenellaceae_R-7_group, complement 3, and complement 4 (P < 0.05), while 12-dehydrocholic acid and 7-ketodeoxycholic acid positively correlated with Bacteroidota and IL-10 (P < 0.01). In conclusion, OEO and sublancin individually improved physiological status of goat kids via modulating colonic microbiota-BA metabolism, whereas their half-dose combination requires an optimized ratio.