The Thai Journal of Veterinary Medicine


In order to prove the effect of “fixed time service”, this study aimed to determine reproductive efficiency of hormone manipulation to induce ovulation and improve pregnancy rate. Estrus cycles of fifty mares were monitored every other day until ovulation by ultrasound (control group). Six days after ovulation, all mares received 5 mg prostaglandin F2a in order to synchronize estrus cycle. Reproductive tract monitoring was continued until the follicle reached the size of 35 mm and uterine edema was scored 2. Then, the mares were randomly assigned into four groups and treated with different ovulation stimulation methods: T1, spontaneous ovulation (n=10); T2, single dose of 40 g Buserelin (n=15); T3, single dose of 1500 IU hCG (n=15); and T4, single dose of 3000 IU hCG (n=10). The ultrasonography monitoring was conducted daily in each mare, and the sizes of follicles were recorded. Results showed that interovulatory intervals in the control group and the prostaglandin F2a-treated group (T2) were 20.87 and 14.83 days, respectively. The growth of follicle per day was lowest in the control group when compared to the treatment groups, of which the group treated with GnRH analogue (T3) gave the highest growth rate (6.5 mm). The duration from treatment to ovulation date in T3 (1.53 days) and T2 (1.83 days) was significantly earlier than that of T1 (3.2 days) and T4 (2.1 days). For all mares that were treated with 1500 IU hCG (T3), the ovulation occurred within 48 h and 93.33% of them were pregnant. In conclusion, the treatment with 1500 IU hCG, iv provided the shortest mean number of days from administration until ovulation and the highest pregnancy rate (93.33%).

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