In order to study the effect of the changes the voluntary waiting period on production and reproductive traits and estimating optimal voluntary waiting period, biological information and economic data collected from 30 Holstein dairy herds located in Isfahan provinces during 1992 to 2013 were used. The data evaluated in SAS software. Results showed that the animal health status at the time of insemination is the most important factor considered by breeders. Based on the results, the timing of insemination according to the season and heat stress, due to increase calving to first service, open days and the number of insemination (P 0.05). The results indicated the presence of a full-time veterinarian has significant positive impact on the farms (P 0.05) to improve the reproductive performance of the herd. Based on the results obtained in this study, with an increase in voluntary waiting period, days open, calving interval increased dry period and show that the number of inseminations and 305-day milk production decreases. A population represntive characteristics of Iranian Holstein dairy cattle, was simulated using Monte Carlo method. To increase accuracy, the simulation was repeated 30 courses and 1,000 cattle were created for each period. The optimal amount of voluntary waiting period taking into account the biological and economic factors were determined. Simulation results show an increase in voluntary waiting period would reduce the number of inseminations, the number of calves per year and annual milk production occurs. The results of this study, the optimal value for the optional voluntary waiting period about 60 to 70 days after calving were determined; the longer this period of economic efficiency, due to reduced milk production and reduced the number of calves per year. The longer this period of economic efficiency, due to reduce milk production and reduced the number of calves per year. The results of this study could change the attitudes of farmers and professionals to pay more attention to voluntary waiting period as a management tools to improve the reproductive performance of dairy cattle country. Keywords: voluntary waiting period, Days to first service, Optimizing, Monte Carlo simulation