A study on subcutaneous infection model of colibacillosis in broilers: Selected immunological and hematological aspects

Colibacillosis is still a major challenge to poultry industry. This study examined selected immune and hematological features of broilers experimentally infected with <i>E. coli</i> via subcutaneous (sc) route. Fifty-one 5-week-old chickens were randomly assigned to three groups: two controls (NC and SCC) and one experimental (SC) group. The SC group was inoculated by O2 <i>E. coli</i> suspension via sc route in the inguinal region. Three days after inoculation, blood sampling was performed. Bacterial count of liver was determined. Histopathological samples of liver, lung, spleen, thymus, and bursa were also collected. Serum total protein and globulin significantly increased in birds of SC group as compared to control birds (<i>P</i> < 0.05). Birds in SC group also showed decreased albumin/globulin ratio. Serum levels of IL-6, IL-10, and IFN-γ remained statistically the same among groups. Lymphocytosis, monocytosis, thrombocytosis and heterophilia were present in SC group. Heterophils/lymphocytes ratio increased in SC birds. Left shift was observed in SC group with cells showing vacuolated cytoplasm that contained toxic granules. Histologically, lung involvement was less severe than liver. Lymphoid depletion was present in all examined lymphoid organs. <i>E. coli</i> growth was observed in liver samples from SC group but not in control birds. In conclusion, using sc route for induction of colibacillosis was associated with a systemic inflammatory response in broilers and histopathological lesions of thymus, bursa, and spleen three days post-infection. It seems that detection of changes in serum cytokine levels (IL-6, IL-10, and IFN-γ) should be performed in earlier hours of the disease in this model.