9. Ovine DRB1 Polymorphism and Its Associations with Body Weight, Milk Contents and Immunological Parameters

The DRB1 gene is known as a part of the Major Histocompatibility Complex (MHC) with important effects on disease resistance and immunological response in mammals. Single strand conformational polymorphism (SSCP) analysis and direct DNA sequencing methods were employed to study the second exon of DRB1 gene polymorphism in Mehraban and Lori-Bakhtiari sheep, using 155 Mehraban and 167 Lori-Bakhtiari (totally 322) ewes. Eleven different SSCP patterns with 26 SNPs (five new mutations) were found in both breeds. Associations of different genotypes with some traits including body weight, milk contents, milk somatic cell count and some immunological parameters were also studied. The observed genotypes had significant associations (P<0.05) with immunological parameters including serum total protein, α2-globulin, β-globulin, γ-globulin and total globulins and body weight at 3 months of age (weaning). The effects of the genotypes on serum albumin and α1-globulin, body weights at 9 and 12 months of age and milk lactose tended to be significant (P<0.10). The results of the present study indicated that the DRB1 exon 2 is highly polymorphic and could be considered as an important fragment in marker assisted selection, especially for improvement of immunity in sheep.