Ultrasonographic Observation of Individual Follicular Development in Japanese Black Cows Superovulated with FSH

In order to clarify the individual follicular development during superovulation treatment in Japanese black cows, consecutive ultrasonography was performed. A total of 5 cows was superovulated in mid-luteal phase. Ovaries were monitored with ultrasonography at 12 h intervals from the initial FSH injection (=0 h) until 24 h after the first ovulations. All follicles more than 5 mm in diameter were determined in freezing ultrasonography images with built-in calipers. Blood samples were collected at 12 h intervals for 168 h and the concentrations of progesterone and estradiol-17β were determined. Few follicles more than 5 mm in diameter emerged at 12 h after FSH injection, but most follicles more than 5 mm in diameter emerged at 36 h. Then, these emergence tended to decrease gradually. Every ovulatory follicles were retrospectively identified more than 5 mm in diameter at 84 h. The follicles that emerged later tended to grow faster than those emerged earlier within 84 h after treatment. The progesterone profile after prostaglandin F2α (PG) injection in superovulated cows was similar to those in normal cycling cows synchronized with PG. The estradiol-17β profile showed a slight increase between 0 and 72 h during the follicular growth, then the levels reached peaks in accordance with estrous behavior prior to a sharp decrease before ovulation.