A linkage disequilibrium approach with microsatellites was employed to investigate QTL affecting immune response. Highly inbred males of two MHC-congenic Fayoumi chicken lines were mated with highly inbred G-B1 Leghorn hens. Adult F2 hens (n = 158) were injected twice with SRBC and fixed Brucella abortus (BA). Agglutinating antibody titers were measured. Secondary phase parameters of maximum titers (Ymax) and time (Tmax) needed to achieve Ymax were estimated from postsecondary titers by using a nonlinear regression model. A three-step genotype strategy (DNA pooling, selective genotyping, and whole population genotyping) was used to identify microsatellite markers that are associated with immune response to SRBC and BA. The linkage distances between adjacent markers in the F2 population were estimated by Crimap. The QTL affecting immune response to SRBC and BA were detected based on F statistic by interval mapping. A total of five significant QTL, as determined by a permutation test, were detected at the 5% chromosome-wise level on Chromosomes 3, 5, 6, and Z. Two (Chromosome 3 and 6) of five QTL were significant at the 1% chromosome-wise level. The variance explained by the QTL ranged from 6.46 to 7.50%. The results suggest that regions on Chromosomes 3, 5, 6, and Z contain QTL that affect antibody kinetics in the hen.
Agglutination Tests Animals