Abstract

Improving the efficiency of milk production and its constituents without increasing the size of the dairy herd is the foremost goal of the selection in dairy industry. The use of polymorphic genes as detectable molecular markers is a promising alternative to the current methods of trait selection once these genes are proven to be associated with traits of interest in animals. Beta-lactoglobulin (Β-LG) is one of the most important genes that play a crucial role in the milk quality and coagulation process of cheese and butter. Identification of different Β-LG genotypes and association with different milk performance traits in Egyptian Holstein cattle was performed through Polymerase Chain Reaction-Restriction Fragment Length Polymorphism (PCR-RFLP) and DNA sequencing of two hundred blood samples. Digestion of 447bp PCR product with Hae III restriction enzyme revealed three genotypes (AA, AB, BB), with higher frequency of B allele (64%) than A allele (36%). Nucleotide sequence analysis of different genotypes revealed two point mutation at exon four, one of them (T301C) corresponding to the same amino acid asparagine and the other Single Nucleotide Polymorphism (SNP) (C390T) represented a non-synonymous mutation producing amino acid change of alanine to valine. Animals with genotype AA had more milk yield and protein % (11461kg and 3.45) respectively, while BB genotype recorded higher fat % (3.85). The information given in the present study will be extremely helpful for improving milk production traits in dairy cattle by marker-assisted selection and outlined a strategy to avoid long and costly traditional selection methods for dairy purposes in Holstein cattle.

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