Energy-sparing effect of oregano (Origanum vulgare subsp. hirtum) essential oil and its mixtures in broilers: Improved feed efficiency via optimized intestinal health.

The study aimed to investigate the energy-saving effects of oregano essential oil and its compounds in low-metabolizable-energy diets for broilers. A total of 600 one-day-old Arbor Acres broilers of similar body weight were randomly assigned to five dietary treatments, each consisting of six replicates with 20 birds per replicate, over a 42-day trial period. The control group (Ctrl) received a basal diet, whereas the low-energy group (LC) was fed a diet with ME reduced by 210 kJ/kg relative to the Ctrl group. Three supplemented groups were formulated based on the LC diet: LCO (LC + 200 mg/kg oregano essential oil, OEO), LCT (LC + 200 mg/kg oregano-clove essential oil composite, OEC), and LCM (LC + 1000 mg/kg oregano essential oil-lauric acid composite, OEL). Results revealed that reducing dietary metabolizable energy (ME) increased the feed-to-gain ratio (F/G) throughout the trial period. However, supplementation with essential oils on the low-energy diet significantly decreased F/G, enhanced antioxidant enzyme activities, increased secretory immunoglobulin A (SIgA) levels in the duodenum and ileum, and reduced inflammatory cytokine levels in the intestinal mucosa (P < 0.05). Morphologically, essential oils improved intestinal structure by increasing villus height, decreasing crypt depth, and elevating the villus-height-to-crypt-depth ratio (VH:CD). Furthermore, OEC and OEL treatments promoted intestinal health by increasing fecal Lactobacillus counts while reducing Escherichia coli and Salmonella counts (P < 0.05). 16S rRNA analysis further demonstrated that OEC and OEL enhanced microbial diversity and modulated the composition of the cecal microbiota. In summary, oregano essential oil and its compounds can mitigate the adverse effects of low-metabolizable-energy diets by promoting intestinal development, modulating gut microbiota, and enhancing antioxidant and immune functions. The oregano essential oil-lauric acid complex demonstrated particularly notable effects, providing new insights for developing energy-saving feed additives.