Genetic polymorphism in β-lactoglobulin gene of some sheep breeds in the Kingdom of Saudi Arabia (KSA) and its influence on milk composition

beta -Lactoglobulin ( beta -Lg) is one of the most important proteins in mammals' milk. It plays a crucial role in milk quality. The polymorphism of < beta -Lg gene can be used as a marker system. To analyze the genotype distribution of beta -Lg gene in some sheep breeds reared in Taif region of Saudi Arabia and its influence on milk composition, sixty (60) animals belonging to four sheep breeds named Noami, Sawakni, Harry and Nagdi, were utilized. The polymerase chain reaction-restriction fragment length polymorphism (PCR-RFLP) test was performed and genetic polymorphism was detected by the digestion of a 452 bp PCR fragment of exon II of beta -Lg gene with the endonuclease Rsal. The results revealed that Noami and Sawakni breeds belong to beta -Lg-A genotype while Harry and Nagdi belong to genotype beta -Lg Sequence analysis of a 340 bp fragment in the promoter region of beta -Lg showed polymorphism among the examined breeds. Analysis of milk composition in the different breeds indicated that the total protein content of milk was the highest in Noami breed followed by Sawakni, Nagdi and Harry. Concerning milk total fat and total solids contents, Harry breed was the highest, while no significant difference was evident among different breeds in lactose or non-fat solid contents. These results indicate the feasibility of PCR-RFLP test for differentiating sheep breeds and the existence of a significant relationship between beta -Lg-A genotype and total milk protein content while no clear association between beta -Lg genotypes and other milk content was proved.