Antibodies levels in day old chicks (d.1) and 28 d in the control (C) and vaccinated (V) groups (n = 10 per group).

Antibody was measured by Haemagglutination-Inhibition test and mean titer expressed as log 2 of serum serial dilution. Statistical differences between groups indicated as bars with star (** = P ≤ 0.01).