Development of cell-mediated immunity and resistance to clinical coccidiosis infection in chickens selected for resistance and susceptibility to Eimeria tenella.

The development of cell-mediated immunity (CMI) and resistance to clinical coccidiosis was determined in Auburn Strain Leghorn chickens previously selected for resistance and susceptibility to Eimeria tenella. Auburn Strain Leghorns selected for resistance (R Line) developed CMI and resistance to E. tenella challenge 2 weeks after receiving a commercial coccidiosis vaccine (CocciVac D). In contrast, Auburn Strain Leghorns selected for E. tenella susceptibility (S Line) did not develop significant CMI or resistance to clinical challenge infection until 6 weeks after receiving CocciVac D. The CMI was measured by the ability of chickens to develop a delayed hypersensitivity (DH) skin test response to an Eimeria oocyst antigen extract. Resistance to coccidiosis challenge infection was measured by percent weight gain, lesion scores, fecal scores, mortality, and oocyst output per gram of cecal contents at 7 days after challenge. Our research indicates that there is a strong correlation between innate resistance to coccidiosis and the ability of the chicken to recognize and mount a DH response to the parasite.