Changes in Blood Levels of Estradiol-17.BETA. before Induced Ovulation, Leading to Luteal Hypoplasia in Cows.

Corpus luteum formed in cows after ovulation induced by the use of prostaglandin (PGF2α) and gonadotropin releasing hormone (GnRH) showed hypoplasia. In the present study, peripheral blood levels of estradiol-17β (E2) were determined in the cow in which ovulation leading to luteal hypoplasia was induced. Ovulation was induced in 6 cows by injecting GnRH 32 h after the injection of PGF2α analogue (PGF2α-A) at 8 to 11 days after spontaneous ovulation. The animals were divided into 2 groups of 3 each. In one group, FSH was injected twice at 16 h intervals, starting 0 h after PGF2α treatment. Cows in the other group were not injucted. Progesterone (P4) values in blood remained low even after the induced ovulation in all 3 cows of the group not injected with FSH. Blood P4 levels increased gradually and remained at a high level after induced ovulation in all 3 cows treated with FSH. E2 values in the FSH injection group increased and peaked at 8 h after GnRH injection. At this time, average levels of E2 were 9.1 and 4.7 pg/ml in FSH treated and non-treated group, respectively, and the difference was significant (P<0.01). These results suggest that the ability of the follicle to secrete estrogen before ovulation, which causes luteal hypoplasia, is low.