Abstrakt: |
Changes in echotexture and blood flow in the wall of preovulatory follicles in heifers were studied in relation to the LH surge and ovulation in gonadotrophin-releasing hormone-induced (n= 7; Experiment 1) and spontaneous (n= 8; Experiment 2) ovulators. Ultrasonographic examinations and blood sampling were performed either every hour (Experiment 1) or every 6 h (Experiment 2). The interval from LH peak to ovulation in induced and spontaneous ovulators was 27.1 ± 0.3 and 34.5 ± 1.5 h, respectively. Follicle diameter did not increase between the LH peak and ovulation. In the induced ovulators, serration of the stratum granulosum was detected in one (14%), two (29%), three (43%) and four (57%) heifers at 4, 3, 2 and 1 h before ovulation, respectively. An initial increase in blood flow (P< 0.001) encompassed the LH peak in both experiments. In the induced ovulators, blood flow increased (P< 0.02) to maximum 3 h after the LH peak, maintained a plateau for 5 h, decreased (P< 0.05) between 9 and 14 h, increased (P< 0.05) again between 19 and 21 h and then decreased (P< 0.01) between 25 and 26 h (1 h before ovulation). The biphasic increase and decrease in blood flow and serration of the granulosum in the wall of the preovulatory follicle in cattle are novel findings. [ABSTRACT FROM AUTHOR] |