THE APPLICATION OF PROGESTERONE-CONTAINING CIDRTM DEVICES TO SUPEROVULATED EWES

Two trials were used to investigate the application of CIDRs to synchronize superovulated ewes. In Trial 1, CIDRs were inserted into 42 ewes for 12 d. Gonadotrophin treatment began on the morning of Day 10 with 800 I.U. pregnant mare serum gonadotrophin (PMSG) given as a single injection, and either 12 or 18 mg follicle stimulating hormone (FSH) given in decreasing dosage injections twice daily over 3 d. The CIDR devices were withdrawn at the last FSH injection. The ovulation rate and total ovarian response (ovulations + large, cystic or luteinized follicles) were recorded on Day 6 after estrus. Trial 2 used a 3×2×2 factorial design (n = 169) to investigate three 12 d synchronization treatments; one vs two CIDR devices (where the first device was replaced with a new device on Day 9 vs a progesterone-impregnated sponge); two frequencies of FSH injection (once vs twice daily); and two doses of FSH (12 vs 18 mg). The ewes also received 800 IU PMSG on the morning of Day 10. The ewes were mated with fertile rams and the data collected included the parameters in Trial 1 as well as results from surgical ova collections. Results from both trials suggest that abnormal follicular development occurs when superovulatory gonadotrophin regimens are delivered during synchronization with a single, 12 d CIDR device. This was evident from the high proportion of abnormal follicular structures present at the time of observation in Trial 1. In Trial 2, a reduction in ovarian response was observed in ewes treated with the higher dosage of gonadotrophin and a single CIDR device than those treated with two devices, whereas little difference was observed across synchronization treatments in response to the lower level of gonadotrophin. There was no difference in ovarian response between ewes treated with two CIDR devices and those treated with sponges. Increasing the frequency of FSH administration from once to twice daily and the dose of FSH from 12 to 18 mg significantly increased both ovulation rate and the total ovarian response. This led to a higher number of ova recovered and of transferable embryos. Ewes synchronized with CIDR devices exhibited estrus earlier after pessary withdrawal than ewes treated with sponges. © 1990.