Post-vaccination response could impair animal fertility and causes economic losses. To verify the possible consequences of IBR vaccination, Holstein cows (n= 840) from 1st-3rd lactations vaccinated with polyvalent modified-live viral vaccine were included in this investigation. Cows were allocated to Pre-vac. (n=82; inseminated Day-36 to Day-18), around vac. (n=133; inseminated Day-17 to Day+3) and post-vac. (n=363; inseminated from Day+4 to Day+60) groups according to insemination time related to the day of IBR vaccination (Zero day). The number of inseminations/conception, return to service rate, pregnancy rate, days return to service, and milk production were recorded. Results showed that 3-week return, and 90-day return rates were maximal in the around vac. (45%) and pre-vac. (50%) groups, respectively. At the 2nd insemination, the around-vac and post-vac inseminated animals decreased compared to pre-vac. The return to insemination in the around-vac, post-vac and pre-vac groups was 69%, 63% and 59%, respectively, during the first 45 days post-insemination. The return to service (days) was 31.74±2.46, 23.61±1.87, 27.10±1.39 in pre-vac, around-vac and post-vac groups, respectively. The synchronization and insemination extra cost/100 cows during the pregnancy period were maximal in the pre-vac. group (27590 &17800 EGP, respectively), but least in the post-vac. group (22010 &14200 EGP, respectively). In conclusion, MLV IBR vaccination showed a transit effect on fertility and results in economic losses. This study spotted the light to the interaction between IBR vaccination and insemination timing to avoid any conception failure and extra costs to dairy farm profitability.