Genetic Variation in Hypothalamic-Pituitary Axis Candidate Genes and Their Effects on Milk Production Traits in Iranian Holstein Cattle

This study investigated the polymorphism of hypothalamic-pituitary axis genes and their effects on milk production traits. To this end, we used genomic information of 134 animals. The studied genes were prolactin (PRL), growth hormone (GH), pituitary transcription factor (Pit-1), and signal transducers and activators of transcription (STAT5a). Genomic DNA was isolated from semen, and the existing genotypes for all studied genes were identified using PCR-RFLP assay. The frequencies of the genotypes AA, AG, and GG of PRL- Rsa I, LL, LV, and VV of GH- Alu I, AA, AB, and BB of Pit1- Hin fI, and TT, TC, and CC of STAT5a- Ava I were 0.754, 0.246, and 0, 0.873, 0.127, and 0, 0.142, 0.358, and 0.500, and 0, 0.261, and 0.739, respectively. The genotypes of PRL- Rsa I, GH- Alu I, and STAT5a- Ava I were in the Hardy–Weinberg equilibrium ( P > 0.05), except for Pit1- Hin fI ( P < 0.05). The association of Pit1- Hin fI and STAT5a- Ava lI gene polymorphisms with milk fat yield (MFY) and milk protein yield (MPY) was significant ( P < 0.05). However, no effective association ( P < 0.05) was observed between genotypes and other studied traits. The results suggest that Pit1- Hin fI and STAT5a- Ava lI polymorphisms can be used as possible candidates in selecting some milk protein production traits, such as MFY and MPY.