Association between growth hormone receptor AluI polymorphism and fertility of Holstein cows.

The aim of this work was to determine the effects of a growth hormone receptor (GHR) AluI polymorphism on the reproductive performance of Holstein cows. The cows (n = 94) were on the study from 3 weeks prepartum until 210 days in milk (DIM). Blood samples were collected at -21, 0, 7, 21, and 60 DIM. For GHR genotyping, DNA was extracted from blood and the presence of the alleles determined after polymerase chain reaction and digestion with the restriction enzyme AluI. Milk samples were collected for progesterone analysis and detection of ovulation until first breeding. Cows were submitted to an OvSynch-TAI protocol at 55 DIM that was repeated for cows diagnosed as not pregnant. Data were analyzed with SAS for polynomial effects of the presence of 0, 1, or 2 GHR AluI (-) alleles. Among the cows, 37% had the AluI(+/+) genotype, 51% had AluI(-/+), and 12% were AluI(-/-). Interval from calving to first ovulation was not different among genotypes (P > 0.05). Cows carrying at least one GHR AluI(-) allele had fewer number of services per conception (P = 0.02). In addition, there was a linear reduction (P = 0.02) in the calving to conception interval among genotypes with fewest days for GHR AluI(-/-) cows. GHR AluI(-/-) cows also had the highest serum IGF-I concentrations (P = 0.03). Milk production and composition were not different among genotypes (P > 0.05). The presence of one or two GHR AluI(-) alleles in Holstein cows was associated with a linear reduction in the calving to conception interval and a reduction in the number of AI/conception.