Effect of Estradiol-17β on Superovulatory Treatment with CIDR and FSH in Japanese Black Heifers

The aims of the present study were to examine the effect of injection of estradiol-17βvalerate (EV) on superovulatory treatment with CIDR-B (CIDR) and FSH in Japanese Black heifers and the effect of repeated superovulatory treatments at a short time interval. Sixteen heifers were allocated ramdomly to the following two treatments, treatment 1 and treatment 2. Each heifer received CIDR in the vagina regardless the day of estrus cycle. On the following day heifers allocated to treatment 1 were injected intramuscularly with EV 5mg dissolved in 2ml of sesame oil. Similarly heifers allocated to treatment 2 were injected intramuscularly with 2ml of sesame oil as a vehicle. Treatment 2 served as control. Superovulatory treatment was started on day 5 after the EV/sesame oil injection. Briefly, heifers received intramuscularly 20 AU FSH in a decreasing manner for 3 days. On day 3 after the first injection of FSH, CIDR was removed from each heifer and simultaneously 750μg cloprostenol was injected intramuscularly. When heifers showed estrus, the cows were inseminated artificially with frozen semen twice at an interval of 12h. Embryo collection was carried out nonsurgically on day 7 after showing standing estrus. A combination of the superovulatory treatment and the embryo collection was one round. In total, four rounds were performed reversing treatments at each round. An interval of embryo collection was uniformly 28 days. At 3rd and 4th rounds the number of donor heifers were 12 as a result of removal of 4 donors. At 1st and 2nd rounds follicular dynamics of ovaries were observed every two days from the day of CIDR insertion to the day of CIDR removal with an ultrasonography. As a result of an analysis of variance with data from 12 heifers during 4 rounds, the number of ova recovered was increased significantly by EV injection (P