Effects of astragalus extract, levamisole and ascorbic acid on humoral immunity in chickens vaccinated with newcastle disease vaccines

This study was designed to assess the effects of Astragalus extract, levamisole and ascorbic acid on the humoral immune response of chickens vaccinated with live and inactivated Newcastle Disease (ND) vaccines. Sixty day-old Cobb500 broiler chicks were used for the study. At day old, the maternally derived antibodies (MDA) to ND virus was determined and the chicks were then housed in a bio-secured pen with water and feed given ad-lib. On the sixth day, the MDA decay was determined thereafter, the chicks were shared into 4 treatment groups. Group A (Astragalus extract); Group B (levamisole); Group C (ascorbic acid) and Group D (Control) of 15 chicks each. Response to ND vaccinations was determined through bleeding to obtain sera for haemagglutination inhibition test at 7 and 14 days except for the second booster with inactivated Komarov vaccine where it was done at 7, 14 and 21 days post vaccination respectively. Antibody titres in the chicks 7 days post first dose of vaccination with La Sota was high in all the treatment groups above the control with 100 % of the chicks having protective antibody titre of ≥4 log₂ until day 30 when the antibody titres in all the groups dropped drastically following the second dose of live La Sota vaccination as the first booster vaccine. However, following the second booster with inactivated Komarov the antibody titres increased in all the treatment groups in comparison to the control especially in groups B and C with GMTs of 5.8 ± 0.19 log₂ and 6.1 ± 0.27 log₂ respectively. We observed that ascorbic acid and Levamisole may have humoral immuno-stimulating effects on vaccinated chickens through yet to be fully explored mechanism. It is recommended that ascorbic acid or levamisole could be used during vaccinations as immuno-stimulating agents to enhance humoral antibody response in vaccinated flocks.