Resistance, susceptibility, and immunity to Eimeria tenella in major histocompatibility (B) complex congenic lines

The major histocompatibility (B) complex influence on resistance, susceptibility, and immunity to Eimeria tenella was examined in UCD B complex congenic chicken lines. In Experiment 1, 6-wk-old chicks from 12 UCD congenic lines were weighed and assigned to either challenge or control groups. The challenge group received a dose of 10,000 E. tenella oocysts. Response to challenge was evaluated by body weight gain and cecal lesion scores. Cecal lesion scores in B3B3 chickens were significantly lower than those of all other genotypes. Genotype B2B2 had the highest lesion scores, which were significantly different from the lesion scores calculated for B3B3, B18B18, and B21B21 chickens but were not significantly different from B14B14, B15B15, B17B17, B19B19, B24B24, BCBC, BJBJ, and BQBQ genotypes. The B21B21 chickens had significantly lower lesion scores than B2B2, B14B14, and BCBC chickens. No other significant lesion score differences were found among the remaining lines. The highest weight gain found in B19B19 chickens was significantly different from that of B3B3, B14B14, B15B15, B17B17, B18B18, B24B24, and BCBC chickens. The B15B15 chickens had the lowest weight gain, which was significantly different from that of B2B2, B19B19, B21B21, B24B24, BJBJ, and BQBQ chickens. Experiment 2 tested the immune response to E. tenella after low dose oocyst immunization. Chicks from 10 UCD 003 congenic lines were divided into three groups: control, challenge, and immune. At 5 wk of age, the immune group was immunized with 500 E. tenella oocysts for 5 consecutive d. Fourteen days after the last immunization all chicks were weighed, and 10,000 E. tenella oocysts were administered to the challenge and immune groups. Significant lesion score differences existed among all three treatments: control (0), immune (2.14 +/- 0.1); challenge (3.13 +/- 0.1). Among immune birds, B3B3 and BQBQ chickens had significantly lower lesion scores than B19B19, B24B24, B14B14, and B2B2 chickens