Comparison of resistance level and circulating IgG response in chickens experimentally inoculated with a multiple or single immunizing doses of Eimeria acervulina.

Two immunizing methods (Trickle or single immunizing doses) against E. acervulina were tested in chickens. The effects of immunization and challenge upon growth, oocyst output and circulating antibodies response (IgG) were compared. Neither immunization method produced pathogenic effects, similar numbers of oocysts were produced, and the levels of IgG in serum were similar and low in each case. After the challenge, immunized birds showed a high level of resistance but susceptible controls produced very large number of oocysts and showed a marked reduction in the growth. Birds immunized by a trickle infection produced oocysts on two days only and the total number of oocysts per bird was very low, whereas those immunized by a single infection produced oocysts over a period of nine days and the total number of oocysts was higher. Susceptible and birds immunized by a single inoculation showed similar IgG concentration and these were statistically higher than birds immunized by a trickle infection. In susceptible birds the kinetic of IgG was delayed about 4 days.