Blood flow and echotextural differences between the future dominant and subordinate follicles before the beginning of diameter deviation in heifers

•Blood flow in the future dominant follicle increased before diameter deviation.•An anechoic layer is described for follicles ≥6 mm.•Anechoic layer was related to follicle diameter and not to status.

Diameter deviation is the beginning of a decrease in growth rate of the largest subordinate follicle (SF) and a continuing growth rate of the dominant follicle (DF). In wave 1 in cattle, deviation begins 2 or 3 days after ovulation when the future DF is about 8.5 mm. Gray scale and power-flow Doppler ultrasound examinations were done in experiment 1 (daily examinations, n = 13) and experiment 2 (examinations every 8 h, n = 15). Blood flow and an anechoic layer in the follicle wall were normalized to the beginning of diameter deviation (day 0 or hour 0). Only waves with conventional diameter deviation (68% of waves) were used as identified by: (1) future SF greater than 7.0 mm when DF was 8.5 mm and (2) future DF and SF did not switch in diameter rank. In experiment 1, deviations in the extent of blood-flow signals and in the extent of anechoic layer began on the same day as deviation in diameter. In experiment 2, deviations in diameter, surface area (πd2), and anechoic layer began in synchrony, and deviation in blood-flow signals began 16 h earlier. Blood-flow deviation before diameter deviation was shown by (1) a first difference (P < 0.02) between follicles at hour −16 and (2) development during the hours −24 to 0 of a greater (P < 0.05) percentage difference between follicles in blood-flow signals (11.1 ± 2.3%) than in surface area (7.4 ± 0.7%) or diameter (4.5 ± 0.4%). Results supported the hypothesis that the extent of blood flow in the future dominant and subordinate follicles deviates before diameter deviates. A similar hypothesis for anechoic layer was not supported; diameter and anechoic layer deviated in synchrony.