Evaluation of hematological variables in layer pullets after vaccination and challenge with E. coli

Avian colibacillosis is the most common bacterial disease in poultry. Vaccination has been extensively used in order to protect birds from colibacillosis infection. The aims of this study were to assess hematological alterations in commercial layer pullets after intratracheal challenge with a pathogenic strain of Escherichia coli as well as to investigate the differences observed between birds vaccinated with different vaccination schemes against avian colibacillosis. Four groups of conventional pullets were reared in the same house following different vaccination protocols against colibacillosis. Birds in group A received no vaccination. Birds in group B received 3 applications of a commercial live O78 vaccine. Birds in group C received 2 intramuscular applications of an autogenous vaccine consisting of an O78, an O111, and an O18 E. coli strain, while birds in group D received 2 applications of the commercial vaccine and one application of the autogenous. All birds were inoculated intratracheally with a pathogenic O78 E. coli strain. Whole blood samples were collected before challenge and 1 week after and hematological evaluations of packed cell volume (PCV), total white blood cell count (TWBC), differential leukocyte count, heterophil/lymphocyte ratio, and cell morphology were performed. Only slight alterations occurred in PCV in all groups. After challenge, a significant elevation was observed in TWBC and number of heterophils, lymphocytes, monocytes, and heterophil/lymphocyte ratio in all four groups. Furthermore, toxic heterophils were more frequently observed after challenge in groups A and B. Those results indicate that birds in groups C and D were better protected from E. coli infection in comparison to groups A and B.