Abstract
Colibacillosis, a major bacterial disease affecting chickens and turkeys, is caused by avian pathogenic Escherichia coli (APEC). The disease has significant economic implications for poultry farms, resulting in increased mortality, reduced body weight, and higher feed conversion ratios (FCRs). These factors can lead to higher carcass condemnation at slaughterhouses.In recent years, significant progress has been made in the development of vaccines against APEC, including both homologous and heterologous vaccines. The present study employed mineral oil as an adjuvant for inactivated E. coli, which was inoculated via injection route to layer chickens.At 28 days of age, 60 birds were subsequently divided into six experimental groups of 10 chickens per group. The control group did not receive the E. coli vaccine, whereas the five treatment groups were vaccinated subcutaneously with a formalin-inactivated, mineral-oil adjuvant E. coli vaccine containing an isolate of E. coli serotype O(78). The T1, T2, T3, T4, and T5 groups were vaccinated at The T1, T2, T3, T4 and T5 groups were inoculated at 28 days of age with 0.2 ml (8 ×10(6), 16 ×10(6), 33 ×10(6), 66 ×10(6) and 133 ×10(6) cfu/ml) of E. coli O(78), respectively.Ten weeks after inoculation, the levels of IgG antibody titres against E. coli were evaluated using an ELISA method. The results demonstrated a significant increase in IgG antibody titres in the immunised birds compared to the unimmunised control group (P <0.05). Anti-IgG antibodies increased on a weekly basis after injection in most vaccinated groups up to four weeks.In conclusion, the prepared E. coli vaccine at the Razi Institute, Shiraz branch, induced high levels of immune responses in the vaccinated group, as revealed by ELISA. In order to elicit a substantial immunological stimulus, it is recommended that all chickens in the experimental group receive a booster dose four weeks after the initial immunization.