Research articleAssociation between polymorphisms in somatotropic axis genes and fertility of Holstein dairy cows

The aim of this study was to determine the effect of growth hormone receptor (GHR) AluI, insulin-like growth factor type 1 (IGF-I) SnaBI, and signal transducer and activator 5A (STAT5A) BstEII polymorphisms in the reproductive performance of Holstein dairy cows and the frequency of this genotypes in cows managed in different systems. This work studied 381 and 506 Holstein cows from semiextensive and intensive systems, respectively. The frequency of genotypes GHR AluI (+/−), IGF-I SnaBI (−/−) and (+/−), and STAT5A BstEII (−/−) was higher in animals from semiextensive system, whereas the frequency of the genotypes GHR AluI (+/+) and IGF-I SnaBI (+/+) was higher in animals from intensive system (P < 0.05). In the intensive system, cows from the STAT5A BstEII (−/−) genotype had a longer calving-first heat interval (P = 0.03). In conclusion, there was no association between the genotypes of GHR AluI and IGF-I SnaBI and fertility of Holstein cows raised in semiextensive or intensive regimes, although the genotype frequencies of the evaluated polymorphisms were different between the studied systems. The STAT5A BstEII polymorphism was associated with calving-first heat interval in Holstein cows raised in the intensive system, indicating that this gene could be a molecular marker for genetic selection to improve reproductive performance.