Genetic variation of beta-lactoglobulin (BLG) gene and association studies with milk traits in Mediterranean river buffalo

Beta-lactoglobulin (β-lg) is the major whey protein in ruminants’ milk and in these species has been suggested to play a role also in milk fatty acid metabolism in the newborn. In cattle, sheep and goat the coding gene (BLG) has been well investigated and alleles to this locus were associated with dairy performances. In contrast, data regarding BLG polymorphism and association studies with milk composition traits are scarce in buffalo and carried out only in Indian breeds. Therefore, the aim of the present research was to identify and analyse the variability of the BLG locus in the Italian Mediterranean river buffalo and to test the possible associations between polymorphisms and milk fat traits. For this purpose, individual fresh milk and blood samples were collected from 747 unrelated lactating Mediterranean river buffaloes reared in 14 farms in the province of Salerno, Caserta and Potenza (Italy). Three-hundred and six milk samples were used for FA analysis (fat content, fatty acid composition and fatty acid classes) whereas all blood samples were treated for genomic DNA isolation. We sequenced the entire BLG gene (over 4749 bp, including 789 bp in exonic regions, from exon 1 to exon 7) plus 229 bp of the 5′UTR and 241 bp of 3′UTR of 2 Mediterranean river buffaloes randomly chosen. The sequenced BLG exons had different lengths (from 42 bp for exons 6–179 bp for exon 7) whereas intron lengths ranged from 214 bp (intron 5) to 995 bp (intron 3). Alignments of the sequences among the 2 subjects showed 33 intronic polymorphisms (11 transversions, 11 transitions, 7 deletions/ insertions and 4 inversions) and a transition C→T at the 67th nucleotide of the 5th exon. This mutation identifies a silent allele named BLG A1. Since the transition removes a Hsp92II endonuclease restriction site, the digestion of a PCR product of 353 bp, spanning the 5th exon and part of the 6th exon, allows a correct genotyping. The allele frequency of the BLG A1 allele, determined in 747 subjects was 0.70 (genotype distribution: 53 BLG A/A, 419 A1/A1, 275 A/A1). The present study suggests that no direct effect of the investigated polymorphism exists on these production traits. Although no association was found, the present work provides a starting point for additional association studies between BLG polymorphisms and other phenotypic traits in buffalo, such as milk yield.