Objective  Studying the pathogenicity of serotype O₇₈ Escherichia coli to laying hens with different inoculation methods and the protective effects of single glycerides could provide theoretical support and practical experience for green no-antibiotic chicken breeding.

  Method  The virulence of serotype O₇₈ avian pathogenic Escherichia coli (APEC) strain isolated from a chicken farm in Fujian province was evaluated by oral, subcutaneous and intratracheal inoculation, and the protective effect of water-soluble liquid additive FraC34, composed of butyric and propionic acid monogly cerides, was evaluated in Hy-line laying hens.

  Result  The results showed that:(1)With oral inoculation of 3×10⁹CFU bacteria per chicken, the morbidity was 100% for 12-days old Hy-line laying hens, but no disease detected for 22-days old ones with oral inoculation of 3×10⁹ or 6×10⁹CFU bacteria per chicken. When the 12-days old chicken were inoculated subcutaneously with 0.4×10⁹CFU bacteria per chicken, the rate of the sick was 70%, and 25% for 22-days old ones when inoculated intracheally with 1.5×10⁹ CFU bacteria per chicken. (2)Adding FraC34 in drinking water of laying hens could improve the intestinal tract and reduce the susceptibility to APEC in the early stage. The addition of 2.0-3.0 L·m^-3 FraC34 in drinking water could significantly reduce the morbidity and mortality rate for chickens infected with APEC by oral inoculation and mortality rate of which with intratracheal inner wall inoculation.The daily gain of chicken could be maintained when treated by 3.0 L·m^-3 FraC34.

  Conclusion  The serotype O₇₈ APEC strain was pathogenic to young chicks and led to serious economic losses, but not susceptible for older chicken.FraC34 had protective effect and could maintain the production performance of the chicken infected with APEC, which could be applied instead of some antibiotics for efficient production of poultry.