Polymorphism in β-lactoglobulin gene and its association with dairy goats’ production traits

In the dairy industry, producing milk with greater contents of fat and protein is an important goal. In addition to the phenotypic selection, it is necessary to develop a genetic profile with several polymorphisms located at genes associated with greater percentages of fat and protein in goat milk. These polymorphisms can be used in marker-assisted selection (MAS) for the productive traits of dairy goats. We assessed two polymorphisms already described in the gene that encodes the β-lactoglobulin protein (BLG gene) in goats. One is located at the 5' promoter region of the gene and the other one is located at the exon 7. Besides that, we associated these polymorphisms with productive characteristics of milk from animals of Saanen and Alpine breeds. A sample of 130 Saanen, Alpine and crossbreed goats were randomly chosen to be genotyped for polymorphisms in the BLG gene for PCR-RFLP. To estimate the predicted breeding values, the REMLF90 application was used, and the association between the polymorphism and the predicted breeding value from the animals. In the promoter region, the single nucleotide polymorphism (SNP) at position -60 (C/T) was associated with the percentage of milk proteins, and the TT genotype presented higher breeding values for the protein percentage. We found in the exon 7 region, two very close polymorphisms, a base substitution at position +4601 (S₁/S₂) and a variable number tandem repeat (VNTR) at position +4641 (I₂/I₃). The S₁S₂ genotype showed a higher percentage of milk fat and dry extract when compared to the S₂S₂ genotype, but showed no difference compared to the S₁S₁ for the same trait. Our results pointed out these two polymorphisms, present in the beta-lactoglobulin gene, as candidates to be used in breeding programs to increase both the protein and fat contents of goat milk. Validation tests, however, must be done through genotyping a larger sample of animals