Dietary medium-chain fatty acids mitigate Escherichia coli O78 infection in broilers by enhancing intestinal immune...

Avian colibacillosis caused by Escherichia coli O78 (E. coli O78) compromises poultry health and performance. Medium-chain fatty acids (MCFAs) exhibit antimicrobial and immunomodulatory properties. This study explored the effects of dietary MCFAs on growth performance, intestinal immune function, and microbiota composition in broilers under E. coli O78 challenge. A total of 312 one-day-old male Arbor Acres broilers were randomly assigned to three groups (8 replicates × 13 birds): negative control (NC), E. coli O78-challenged (EC), and E. coli O78-challenged supplemented with 700 mg/kg MCFAs (EM). EC and EM birds were orally challenged with 1 mL of E. coli O78 (2 × 10⁸ CFU/mL) on days 7 and 11; NC birds received 1 mL phosphate-buffered saline (PBS). Compared to the EC, EM broilers had significantly higher body weight (BW) on day 11 and lower feed conversion ratio (FCR) during days 11-18 (P < 0.05). EM birds exhibited a significantly lower spleen index (better immune response) on day 14, but a significantly higher spleen index (immune recovery) on day 21 than the EC group (P < 0.05). In addition, the EM group showed a significantly higher duodenal index (morphological protection) than the other groups on day 21 (P < 0.05). Additionally, EM birds showed significantly increased serum lysozyme (LZM) levels on day 14, elevated endotoxin (ET), IgA, IgM, and reduced diamine oxidase (DAO) levels on day 18 (P < 0.05). IgG levels in the EM group were also higher than those in the EC group on day 21 (P < 0.05). Furthermore, broilers in the EM group exhibited increased jejunal villus height (VH) on day 18 (P < 0.05). The EM group also showed significantly reduced Toll-like receptor 4 (TLR4) expression on day 14 and Interleukin-1 beta (IL-1β) and Interleukin-6 (IL-6) levels on day 18 compared to the EC group (P < 0.05). While no significant changes in ileal microbial diversity were observed in the EM group, the abundances of Lactobacillus spp. and Candidatus_Arthromitus were significantly increased on day 21 (P < 0.05). In conclusion, 700 mg/kg MCFAs supplementation may alleviate the negative effects of E. coli O78 infection in broilers by improving growth, immunity, intestinal integrity, and beneficial gut microbes.