Impact of origin sire (conventional or sexed) and environmental factors on the reproductive traits of Holstein heifers in Isfahan province

The use of sexed sperm is expanding, and there areconcerns about the reproductive future of female calves born from these sperms. Therefore, the aim of this study was to investigate impact of animal sire type (conventional or sexed) and some environmental factors on reproductive traits of Holstein heifers. For this purpose, 35859 records from 22430 Holstein heifers, which had born from 2008 to 2014, were used. The results revealed no significant difference between heifers born from sexed and conventional sperm for conception rate (CR) and mean age at first calving (AFC) traits (P > 0.05); however, the effect of animal sire type was dependent to birth year (P = 0.014) and herd (P = 0.003) management for age at first service (AFS). The factors of herd, birth year and season had a significant effect on the AFS and AFC (P < 0.0001). In general, the effect of season of insemination was not significant on CR (P > 0.05); however, herd, service number, type of sperm (conventional or sexed) and year of insemination affected CR (P < 0.0001). The highest mean conception rate observed in first service and CR decreased about 19% by using sexed sperm compared to conventional sperm. Based on the results of this study, the sire type of heifer had no considerable effect on reproductive traits of heifers. In addition, management of sperm selection was not dependent on the season of insemination and suitable conception rate could be achievable by improving herd management even for sexed sperms.