Analysis of ovarian follicular dynamics during estrous cycles in dairy heifers
1998
Kinoshita, A. (Kagoshima Univ. (Japan)) | Maeda, M. | Kamimura, S. | Ookutsu, S. | Goto, K. | Nakanishi, Y.
Daily ultrasonic monitoring was conducted to examine the dynamics of bovine follicular development categorized into three by their diameter during estrous cycles in dairy heifers. Four dairy heifers were used in this study. Heifers were observed daily during successive two estrous cycles. All cycles consisted of two waves of middle size follicles with only one large follicle (dominant follicle: DF). The number of middle size follicles tended to decrease with the emergence of DF, and new wave of middle size follicles emerged concomitantly with either the regression of a DF or its ovulation. A DF in the second wave was the ovulatory follicle. In the first wave, a DF was first observed on Day 1.4 +- 0.7, ceased its development on Day 8.0 +- 2.3 and became atresia on Day 0.6 +- 2.4. Maximum size of the DF was observed 13.6 +- 1.6 mm in 7 estrous cycles. In the second wave, a DF was observed on Day 12.1 +- 1.2 and ovulated 7.4 +- 1.3 days later. Maximum size of ovulatory follicle reached 14.7 +- 0.5 mm. Additionally, corpus luteum (CL) was observed to regress on Day 14.4 +- 0.7, 3.1 +- 1.5 days after appearance of ovulatory follicle and 6.1 +- 1.0 days before ovulation. During the estrouscycles, 7/14 (50%) of the DF appered in the left ovaries and 7/14 (50%) of DF in the right ovaries. And 5/7 (71%) of DF in the first waves appered ispilateral to the CL, while the ovulatory follicle in the second waves appered 5/7 (71%) in the ovaries contralateral to the CL
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