Association of a genetic marker at the bovine Janus kinase 2 locus (JAK2/RsaI) with milk production traits of four cattle breeds.

In addition to the main components of the somatotrophic axis (GH/GHR/IGF-I/IGF-IR), great importance in the control of growth and development is also attached to the Janus kinase 2 (JAK2) pathway. Induced by the GH/GHR complex, JAK2 activates signal transducer and activator of transcription 5 (STAT5), and in consequence, may be involved in the regulation of expression of insulin-like growth factor I (IGF-I) in the mammary gland. Silent mutation (rs110298451) has been identified within exon 20 using polymerase chain reaction-restriction fragment length polymorphism (PCR-RFLP). A total of 904 individuals of four dairy or dual-purpose breeds (Polish Holstein-Friesian, Montbeliarde, Simmental and Jersey) were genotyped. A genotypic imbalance in the populations was observed. In the case of dual-purpose breeds (Montbeliarde and Simmental), the frequencies of both alleles were almost equal. In contrary, the JAK2G allele was predominant in the Polish Holstein-Friesian breed while JAK2A allele in Jersey. A pronounced relationship between JAK2/RsaI polymorphism and milk production traits was found where, irrespective of breed and lactation order, the GG genotype was significantly associated with higher milk, protein and fat yields, as compared to the AA genotype. Heterozygous individuals were generally characterised by intermediate values of the analysed milk traits. It can be argued that the JAK2 gene polymorphism is a potential marker for milk production traits. However, due to the fact that rs110298451 SNP does not directly affect amino acid sequence, other association studies involving missense mutation should also be performed.