Evolution of alphaS1-casein polymorphism in Italian Alpine and Saanen breeds

Abstract

AlphaS1-casein, coded by CSN1S1 gene, is one of the most important goat milk protein, although, in this species, it represents on average only the 5.6% of the total casein content. On the basis of the milk content of alphaS1-casein, the CSN1S1 variants can be grouped into 4 classes: strong alleles (A, B1, B2, B3, B4, C, H, L, and M), producing almost 3.5 g/L of \uf061S1-casein each; intermediate alleles (E and I; 1.1 g/L); weak alleles (F and G; 0.45 g/L); and null alleles (01, 02, and N) apparently producing no alphaS1-casein. Previous studies have reported that the CSN1S1 can affect casein, protein and fat levels, total solids, milk rheology, as well as cheese yield and quality. The aim of the study was to evaluate how the frequencies of the major CSN1S1 allelic variant have changed during the last 10 years in the two main dairy goat breeds raised in the North of Italy: Italian Alpine and Saanen. Two hundred and twenty three Alpine and 129 Saanen were sampled from 8 farms spread all over Lombardy. AS-PCR and RFLP-PCR were performed to genotype the major allelic variants at the alphaS1-casein locus. Only the Saanen breed proved to be in Hardy-Weinberg equilibrium at this locus. The allele frequencies observed in the present work showed statistically significant differences (\uf0632 test, P<0.005) compared to those reported in two studies published in 2004. This difference was due to an increase of the strong allele A (12 and 18%) and the intermediate allele E (15 and 8%) nearby a reduction of the weak allele F (17 and 12%) and the strong allele B (11 and 13%) respectively in Saanen and Alpine breeds. The A allele is well known for being associated to smaller micellar casein, with a consequent better cheese yield. Recent indications of selection concerning the Alpine and Saanen bucks favours both strong and intermediate alleles, consistent with the described strong frequency increase of CSN1S1*E. For the top farms analysed, with over 85% genotypes with strong alleles, these directive could lead to an increaseof the allele E and consequently to a reduction of protein content and cheese yield