Abstract
Background:
The immune system in chickens has a fundamental role in controlling many diseases based on vaccination, thus enhancement of the immune system response is a priority.
Aim:
The aim of this experiment was to study the effect of probiotics and humic acid on immunity of broiler chickens.
Methods:
Day-old 300 Ross broiler chicks were segregated into 5 groups of 60 chicks per group. Group C was considered as a control. Groups T1, T2, T3, and T4 were given probiotics, antibiotics, humic acid for first 7 days and humic acid for 42 days, respectively. Samples were collected on days 27 and 42 to assess the humoral immunity, cellular immunity, lymphoid organs weight and differential leucocytes count (DLC).
Results:
The results showed a significant increase (P˂0.05) in antibodies titer against Newcastle disease virus (NDV) in chickens given humic acid (T4) daily for 42 days as compared to the control. There was also significant increase of antibodies titer in T1 group given probiotic for the first week lasting up to day 27 as compared to the control. The skin thickness of T4 group showed significant increase as compared to T1 and T2 groups after 24 hours of DNCB challenge. After 48 hours, the thickness was still significantly higher in T4 group as compared to other groups except the control. There were no significant differences in Bursa of Fabricius/Body weight (%) between the groups. Spleen/Body weight (%) was significantly higher in control group and T1 than other groups on day 42. The DLC remains normal in all groups.
Conclusion:
It is concluded that the humic acid has stimulant and strengthening effect of the humoral and cellular immune system when given daily to broiler chickens. Moreover, the use of humic acid and probiotics with good hygiene in the first week of age may alternate the use of antibiotics which could be toxic and raise bacterial resistance.

Key words: Humic acid, Probiotics, Broiler chickens, Humoral immunity, Cellular immunity