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

Abstract

Corpus luteum formed in cows after ovulation induced by the use of prostaglandin (PGF_2α) 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 PGF_2α analogue (PGF_2α-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 PGF_2α 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.