Optimum dose and time of pregnant mare serum gonadotropin injections in Kacang goats to increase endogenous secretion of estrogen and progesterone without superovulation response

The present study was conducted to determine what the optimum dose and time of pregnant mare serum gonadotropin (PMSG) injections in Kacang does to increase endogenous secretion of estrogen and progesterone without increasing the number of ovulating follicles above the normal range. Forty-eight Kacang does were assigned to a 3×4factorial randomized experimental design with 4 replications. The first factor was the dose of PMSG injection, and it consisted of three levels: 0, 7.5, and 15IU/kg body weight (BW). The second factor was the time of PMSG injection at the four stages of follicular development: the pre-luteolytic, luteolytic, pre-antral, and antral stages. The experimental goats were injected twice with prostaglandin to synchronize their estrous cycles. The parameters measured included the number and diameter of the dominant follicles and serum estrogen concentrations during the pre-ovulatory period and the number and diameter of corpora lutea and serum progesterone concentrations during the post-ovulatory period. The diameter of each dominant follicle and corpus luteum was also calculated. The results showed that an increased dose of PMSG injection significantly increased the numbers, total diameters, and diameter of each dominant follicle and corpus luteum, as well as serum estradiol and progesterone concentrations (P<0.05). The time of PMSG injection significantly affected all parameters (P<0.05), except for the diameter of each dominant follicle and corpus luteum. There was a significant effect of the dose and time of injection of PMSG on all parameters, except on the diameter of each dominant follicle and corpus luteum. Average pre-ovulatory serum estrogen concentrations and post-ovulatory serum progesterone concentrations in does injected with 7.5IU/kg BW at the luteolytic stage increased by 133.68% and 545.11%, respectively. Injection of PMSG during the pre-antral and antral stages also increased estradiol and progesterone secretion to a lesser degree without increasing the number of ovulating follicles and corpora lutea. In conclusion, the results of the present study indicate that injection of 7.5IU PMSG/kg BW at the luteolytic stage could be used to increase the secretion of pregnancy hormones without increasing the number of ovulating follicles and corpora lutea above the normal ranges.