GWAS and post GWAS in some reproductive traits in Iranian Holstein heifersers

Improvement of reproductive traits, in addition to the effect on herd reproduction, can be effect on treatment and veterinary costs, animal welfare, and most importantly, profitability. While today, reproduction problems are one of the main reasons for the lack of profitability in dairy cattle herds. The purposes of this study was to Genome Wide association study (GWAS) of Age at First Insemination (AFI) and Age at First Calving (AFC) traits and the Number of Inseminations per Conception (NIPC) in Holstein heifers.In order to conduct this study, the record of 150 heifers born between 1390-1392 was used based on the breeding value of milk production. The results showed that 5 SNPs were significanteffect on age at first insemination (pValue<0.04). which was observed in BTA3(2), BTA5(2), BTA15(2), BTA21, BTA23, BTA28 and BTA30 regions respectively. For the age at first calving, 10 SNPs has a high correlation (pValue<0.04) which was located on BTA3(2), BTA5(2), BTA15(2), BTA21, BTA23, BTA28 and BTA30 regions respectively. 11 SNPs had a high correlation (pValue<0.04) for the Number of Inseminations per Conception and were able to be above the significant threshold line, which were located in BTA11, BTA8, BTA28, BTA6(5), BTA13, BTA18 and BTA14. QTLs identified in the margins of significant SNPs, with body weight trait; calving difficulty, calf weight and heifer maturity age were related. Finally, the QTLs identified in the margins of significant SNPs confirm the fact that the age of the first insemination and the age of the first calving can be effective on production traits, reproduction, longevity and finally on the profitability of the herd. In this situation, it can be said that herd management has a significant role in advancing breeding goals.