Abstract: In order to effectively improve the pregnant rate of ewes, this study developed a method to accurately determine the ovulatory time of small-tailed Han sheep in different reproductive periods by using a commercially available sheep ovulation detector. A total of 60 non-pregnant female small-tailed Han sheep 1. 5-3. 5 years of age (n=30) and 4-6 years of age (n=30) were selected, and the ovulation detector were used to determine and characterize the electrical resistance value of genital tract mucus of the ewes during estrous period. The results showed that the ewes 1. 5-3. 5 years of age had shorter duration of estrous period, and the increase and decrease of the electrical resistance value of genital tract mucus had dramatic variations; the ewes 4-6 years of age had longer duration of estrous period, with a rapid reduction and a zigzag ascent of electrical resistance value of genital tract mucus. By comparing the pregnant rate of ewes after artificial insemination with different ranges of electrical resistance value of genital tract mucus, it was found that the ewes 4-6 years of age had wider range of electrical resistance value of genital tract mucus acceptable for successful pregnancy, and in which the ewes 1. 5-3. 5 years of age had higher pregnant rate than that of the ewes 4-6 years of age. In conclusion, the electrical resistance value of genital tract mucus of the ewes with different ages had varied variation amplitude. Furthermore, the ovulation period in an estrous cycle could be determined when the electrical resistance value of genital tract mucus of the ewes drops to the lowest point and then entered a rising period, and insemination during this duration could obtain higher pregnant rate.

Key words: small-tailed Han sheep, conductivity of genital tract mucus, electrical resistance value, ovulation period, pregnant rate