Abstract: To research the influence of seasons on the superovulation of Holstein, the Holstein heifers of 12 months had been superovulated for 3 times among the year. The results showed that there were no significant differences among seasons for the mean number of the recovered embryos and the degenerated embryos(P>0.05), the mean number of the transferable embroys in march(7.04±4.92) was significantly higher than the data in august (3.20±3.33)(P<0.05), no significant differences with other months(P>0.05). The increased temperature had a negative influence on the effect of superovulation, the success of superovulation could be obtained in th season which was suitable for the cows physilogical functions. It was concluded that the effect of superovulation was related to the seasons, the best season for superovulation was spring, autumn and winter were better than summer, the tropical months should be avoided for superovulation.

Key words: season; Holstein heifers; superovulation