Study on the STAT5A/AvaI polymorphism in Jersey cows and association with milk production traits.

In mammals, the STAT proteins (signal transducers and activators of transcription) are a group of cytoplasmic transcription factors that mediate the actions of many peptide hormones and cytokines within target cells. In this study, the STAT5A/AvaI polymorphism was investigated with the PCR-RFLP technique in a sample of 191 Jersey cows reared in southern Italy. This polymorphism is localized in the coding region of the bovine STAT5A gene. It is a substitution C → T at position 6853 within the exon 7. All the possible genotypes for the C/T polymorphism were identified. The overall frequencies of alleles C and T were 0.75 and 0.25 respectively. In order to study the relationship between this SNP and milk production traits, data for 305-day milk production were used. Significant differences between CC and CT genotypes were found in milk yield (MY), fat yield (FY), solids not fat (SNF) yield, total solids (TS) yield (P < 0.01) and protein yield (PY) (P < 0.05). In particular the CC cows produced more milk than CT ones (6196.07 vs. 5744.66 kg) without differences in protein and fat content. As a consequence, CC cows yielded more fat, protein, solids not fat and total solids than CT. As far as concerns lactose and ash contents and the fat/protein ratio, no significant difference was found between the two genotypes. Even if further studies should be carry out to assess the role of this SNP on production traits, it is possible to conclude that STAT5A/AvaI polymorphism seems to be a promising indirect marker to improve milk production traits in cattle.