The plasma IgG and intestinal sIgA levels in chickens against the outer membrane protein (OMP). A) Plasma IgG levels against specific antigens were determined with the chicken IgG quantitative ELISA. B) The sIgA levels in intestinal wash fluids against OMP antigen were quantified using the chicken IgA quantitative ELISA. Antibody levels were expressed as mean ± S.D. values for each week post-immunization. The values were considered statistically significant, if p values were ≤ 0.05 (*p ≤ 0.05). Group A, non-immunized control; group B, orally immunized; group C, immunized subcutaneously; group D, intramuscularly immunized.