Developmental wave of ovarian follicles and number of follicles in ovaries observed by ultrasonography effect superovulatory response in multiparous Japanese black cattle

A linear-array ultrasound scanner with a 5-MHz electronic linear probe was used for the evaluation of ovarian follicular dynamics during the estrous cycle in multiparous Japanese Black Cattle. The ovaries of 12 donors were monitored daily from the estrous cycle before initiation of superovulation to the estrous cycle during superovulatory treatment. The number of follicles on both ovaries were pooled and follicular patterns were evaluated by grouping the follicles into diameter range of 2-3, 4-6, 7-10, and 10 mm, respectively. All donors (n=18) including 6 extra donor cattles received a total dose of 18 mg FSH in decreasing amounts twice daily for 3 days. Prostaglandin F2alpha analogue was given 48 hours after the initiation of FSH treatment. All the donors exhibiting estrus were artificially inseminated and the embryos were recovered non-surgically 7 days later. The wave of follicles were two-wave (n=9) or three-wave (n=3), and when the presence of 7-10 mm diameter follicles was high, this frequently decreased the number of follicles 2-3 mm diameter. Consequently, donor cattle can be classified into two types, one is composed of cattle with more than ten small follicles and the other is composed of cattle with less then ten small follicles with median follicles. Decreased superovulatory response and ova recovered may have been due to the presence of follicles 7-10 mm diameter which reduce the ability of follicles 2-3 mm diameter to grow into follicles 10 mm diameter during superovulatory treatment as well as number of follicles 2-3 mm diameter. Moreover, high responder animals have higher proportions of good quality embryos than low responder animals. This is probably due to the synchronization of follicular development and ovulation. Bovine ovaries of 18 cows were evaluated ultrasonographically to determine relationships between the number of follicles at the start of superovulation and number of ova