Abstract

This study investigated the haematological changes in vaccinated and unvaccinated laying chickens experimentally infected with a velogenic Newcastle disease virus. Two hundred and forty laying chickens were randomly assigned into four groups of 60 each: vaccinated with Newcastle disease vaccines and infected with velogenic Newcastle disease virus (VI), vaccinated uninfected (VU), unvaccinated infected (UI), unvaccinated uninfected (UU). At peak production, 32-weeks-old, groups VI & UI were each inoculated intramuscularly with 0.2 ml of velogenic Newcastle disease virus. The changes in the blood cells were assayed in the groups on the specified days. The total red blood cell count (RBC) was significantly (P < 0.05) lower in UI group on days 6 & 15 post infection (PI). The packed cell volume (PCV) and haemoglobin concentration (HbC) were significantly (P<0.05) lower in UI group on day 15 PI. There were no significant (P > 0.05) differences between the PCV, RBC and HbC in VI & VU groups from day 0 to 21 PI. The leukogram showed significant (P < 0.05) differences in leukocytosis on days 3 & 6 PI followed by significant (P < 0.05) leukopenia on days 10, 15 & 21 PI in UI group. However, significant leukocytosis on day 10 PI followed by leukopenia on day 15 PI were recorded in VI group.These findings suggest that leukocytosis in UI & VI and decreased haemogram in UI are features of Newcastle disease in laying chickens.

Keywords: Experimental infection, Haematology, Laying chickens, Leukocytosis, Newcastle disease