An association analysis between CSN3 genotype and milk yield in Italian Mediterranean river buffalo

Buffalo milk is characterized by the presence of all 4 casein fractions (alfa-s1, alfa, alfa-s2 and k) encoded by 4 genes (CSN1S1, CSN2, CSN1S2 and CSN3, respectively) mapped on chromosome 7. In particular, k-CN plays a crucial role in the formation of stable casein micelles and has a key influence on milk-clotting. The CSN3 gene is divided into 5 exons of which the exon 4 codes for 160 out of 169 aa of the mature protein. Mutations in this exon are responsible for the quali-quantitative differences of gene expression in cattle. Different studies have been focused on the identification of polymorphisms also in buffaloes. Particularly investigated is the SNP HQ677596:c.536C >T at the nt 377 of the exon 4 that leads to the aa change p.Ile135 > Thr of the mature k-CN. This replacement changes the theoretical MW of the buffalo k-CN from 19,114.7 to 19,102.6 Da; increases hydrophobicity, with the hydropathicity average increasing from -0.526 (Thr) to -0.495 (Ile); and causes the loss of an O-glycosylation site in the variant 135Thr. However, despite the existence of several studies, nowadays the association of CSN3 SNPs with buffalo milk quantity has not still deeply identified. The aim of this study was to evaluate possible effects of the SNP c.536C > T on milk yield (MY) in Mediterranean river buffaloes. A total of 7601 records for MY measured monthly on 1141 lactations of 753 buffaloes belonging to different farms located in Campania region (Italy) were analysed. To estimate the frequencies of this SNP a method based on ACRS-PCR has been adopted. The major allele (c.536C) had a relative frequency of about 0.6 and X2 values showed that there was no evidence of departure from the HWE (p $ 0.05). Association between CSN3 polymorphism and MY was investigated with a mixed linear model that included effects of parity, calving season and month of production. A significant association between c.536C > T and MY was found (p < 0.05). In particular, the CC genotype showed an average daily MY approximately 0.62 kg higher than TT buffaloes. Although such results need to be confirmed with large-scale studies in the same and other buffalo populations, they might offer useful indications for the application of MAS programmes in buffalo and, in the future, they might be of great economic interest for the buffalo dairy industry. In fact, increases in average MY and, consequently, in mozzarella PDO production may be expected.