The Impact of Selected Somatotropic Axis Genes on the Milk Performance Traits of Sheep, Goats and Cattle

The aim of the present article was review of associative research concerning polymorphisms located in growth hormone receptor (GHR), insulin-like growth factor-1 (IGF-1) and Janus kinase 2 (JAK2). Improvement of ruminants production traits is closely related with identification of polymorphisms in the somatotropic axis. This genetic variation can have a positive effect on increasing milk production. The growth hormone receptor effects the metabolism of proteins, carbohydrates and lipids, while Janus kinases as transcription factors directly regulate genes involved in milk secretion in the mammary gland. Genetic factor could have a beneficial effect on increasing milk yield, and therefore, the application of marker-assisted selection can contribute to the faster identification of animals with better genetic predispositions.