ABSTRACT
This study was designed to assess the immune protective effects of the vaccine strain of a precocious line of Eimeria necatrix with different doses and at different immunization times. The immunizations had a negative effect on weight gains of chickens to a certain degree but could be compensated during the “compensatory growth period” after immunity was established in the chickens. The number of oocysts excreted was positively correlated with the immunization dose. All the immunized chickens, whether they were immunized once or twice or immunized with different doses of sporulated oocysts, were able to resist attack from 1x105 virulent sporulated oocysts of E. necatrix. The lesion scoring showed that no significant difference existed in the chicken groups immunized with different doses (300 and 600) of sporulated oocysts. However, a difference existed in the immune homogeneity established in the different immunized groups, and two artificial immunizations were superior to one artificial immunization, indicating that two could extend the duration of oocyst excretion and allow more chances for the immunized chickens to become repeatedly infected.