Genetic variants of CSN1S1 gene in Italian Mediterranean river buffalo: an association with milk yield

Similarly to other species of ruminants, the river buffalo (2n=50) is characterized by the presence of all four casein fractions (??S1, ??, ??S2, and ??) encoded by the four linked autosomal genes (CSN1S1, CSN2, CSN1S2, and CSN3, respectively) mapped on chromosome 7. In particular, the CSN1S1 gene is characterized by an extremely split architecture with 19 exons, many of which of small size (24 bp). It encodes for a precursor of 214 amino acids with a signal peptide of 15 amino acid residues. In recent years, several polymorphisms at milk protein loci associated with traits of economic interest like milk coagulation properties or milk composition have been intensified. Despite that, so far, not any SNP within the milk protein loci was found to be associated with an important trait like milk yield. The aim of this study was to evaluate possible effects of the SNP c.628C>T, identified at position 89 of 17th exon of the CSN1S1 gene and responsible for the amino acid change p.Ser178Leu (A and B allele, respectively) (EMBL n° HE573919-20), on milk yield in Italian Mediterranean river buffaloes. A total of 7547 records for milk yield measured monthly on 1096 lactations of 552 buffaloes belonging to different farms located in Salerno and Caserta province (Southern Italy) were analyzed. Sampling and phenotypic collection data were carried out in collaboration with the Italian National Association of Buffalo Breeders (ANASB). The genotyping of examined animals was carried out by a method based on MboI-ACRS. The major allele (B) had a relative frequency of about 0.6 and ??2 values showed that there was no evidence of departure from the Hardy-Weinberg equilibrium (P???0.05). Association between CSN1S1 polymorphism and milk yield was investigated with a mixed linear model that included effects of parity, calving season and month of production. A significant association between the SNP c.628C>T and milk yield was found (P<0.05). In particular, the BB genotype showed an average daily milk yield approximately 0.61 kg higher than AA buffaloes. The results reported in the present work represent the first example of association between a genetic marker in a milk protein encoding gene and milk yield for the Mediterranean river buffalo. Such association, if confirmed on larger population, should be evaluated in order to supply useful indications for the application of marker-assisted selection programs in river buffaloes.