BACKGROUND: Indigenous chickens could serve as precious genetic resources that should be considered in conservation and breeding programs. The Major Histocompatibility Complex (MHC) has a strong association to disease resistance/susceptibility, production and reproduction traits in chicken. Therefore, identifying its polymorphism in populations under selective breeding could be used for selection of disease resistant and higher productive breeds. MHC association with quantitative traits could be  a result of its linkage with causative genes controlling these traits. Insulin-like growth factor 1 (IGF1) is a candidate marker for phenotypic traits in chicken which are associated with important production and reproduction features. Objectives: Based on this hypothesis, MHC polymorphism and its association to IGF1 gene (as a marker for production traits) were investigated in Khorasan indigenous chicken. Methods: In total, 313 DNA samples that belonged to the Khorasan indigenous chicken were analyzed. LEI0258 microsatellite marker and fragment analysis method was used for MHC genotyping. Single nucleotide polymorphism (SNP) of the IGF1 5’-UTR was detected by restriction fragment length polymorphism (PCR-RFLP) and PstI restriction endonuclease enzyme. Linkage disequilibrium between MHC and IGF1 loci were also determined using SAS/Genetics software and likelihood ratio test. Results: Collectively, 25 different alleles (185-493 bp) and 76 genotypes of LEI0258 microsatellite were identified in Khorasan population. Two alleles, A (PstI -) and B (PstI +) and three genotypes (AA, AB and BB) were identified for IGF1 gene. Significant linkage disequilibrium (p=0.0083) was observed between LEI0258 and IGF1 loci in this population. Conclusions: These results indicate a high MHC genetic diversity in Khorasan indigenous chicken as a valuable genetic resource. Results from MHC/IGF1 linkage study confirm the hypothesis that MHC association with production traits could be as a result of MHC linkage with causative genes controlling the traits.

BACKGROUND: Major histocompatibility complex (MHC) plays a central role in regulation and control of the immune responses to infectious diseases. Due to its polymorphism, individual differences in response to vaccines have been observed in different chicken populations. Studying the association of chicken MHC with immune response to vaccines will help the control of infectious disease and vaccination success. Objectives: The present study aimed to evaluate the MHC polymorphism and its association with antibody response against infectious bursal disease (Gumboro), Newcastle (ND) and Influenza (AI) vaccines in Khorasan native chickens. Methods: Diversity of LEI0258 microsatellite marker (MHC genotyping) was investigated by fragment analysis method. Antibody titer against IBD was measured by ELISA and antibody titers against ND and AI vaccines were measured by Haemaglutination Inhibition (HI) assay. Statistical analysis was performed using SPSS software (version 21). Univariate regression analysis was performed using weighted least squares with weight number of progeny mean data. Results: Total of 13 LEI0258 microsatellite alleles were identified in Khorasan native chickens which indicated a high genetic diversity in the population. The allele 361 bp had the highest (28.48%) and the allele 350 bp had the lowest (0.69%) frequency, respectively. In evaluating the association of MHC with immune responses, 311 and 313 bp alleles were significantly associated with elevated immune responses to Newcastle vaccine, while allele 266 bp was associated with lower IBDV antibody titers (p<0.05). ConclusionS: According to the important role of MHC in controlling infectious disease resistance or susceptibility and quality of immune responses, these results could be used for selection and improving the populations under selective breeding.

BACKGROUND: Major histocompatibility complex (MHC) in chicken has profound influence on resistance/susceptibility to disease, and production and reproduction traits. Microsatellite marker LEI0258 is a genetic indicator for MHC haplotypes. Recognizing diversity of MHC haplotypes in selectively bred populations will be helpful for selecting population resistant to disease and development of effective vaccines. Objectives: The purpose of the present study was to evaluate polymorphism at MHC in two populations of Khorasan indigenous chickens and commercial Leghorn breed using microsatellite marker LEI0258 and to investigate its segregation and heredity. Methods: A total of 335 blood samples from Khorasan Razavi indigenous chickens and commercial Leghorn population including parents (P) and offspring (F1), were analyzed. The MHC genotypes were determined using LEI0258 microsatellite. The study of allele heredity from P to F1 and Hardy-Weinberg equilibrium were conducted using Chi-square and Likelihood Ratio tests. Results: In Khorasan indigenous chickens 20 different alleles were identified for LEI0258 microsatellite. The allele 321 bp had the highest (22.88%) and the allele 182 bp had the lowest (0.16%) frequency. In the commercial population (Leghorn breed) 3 alleles were found for this marker of which the allele 261 bp had the highest (50%) and alleles 487 bp had the lowest (6 %) frequency. In allele heredity analysis and Hardy-Weinberg equilibrium of Khorasan population, no significant differences were observed between P and F1 progenies. ConclusionS: These results indicate a higher genetic variation in indigenous chickens compared to commercial breed. There was no preference for a particular allele in indigenous chickens. The higher frequency of some alleles in F1 population is due to the high frequency of the same alleles in parent population which their gametes make the population gene pool.