Follicle blood flow and FSH concentration associated with variations in characteristics of follicle selection in heifers.

Abstract Selection of the dominant follicle during a follicular wave is manifested by diameter deviation. At deviation (day 0), growth rate continues for the future dominant follicle (F1) and begins to decrease for the largest subordinate follicle (F2). The percentage of color-Doppler blood-flow signals in the wall of F1 and F2 and the temporality between FSH concentration and F1 and F2 diameter were determined daily in waves 1 and 2 in 24 Holstein heifers. Diameter and blood flow were compared among classes of deviation: (1) conventional (F2 ≥ 7.0 mm on day 0), (2) F2-undersized (F2 < 7.0 mm on day 0), and (3) F1,F2-switched (F2 larger than F1 on days −1 or 0). A class-by-day interaction for diameter of F2 (P < 0.004) and for blood-flow percentage of F2 (P < 0.02) represented greatest values on days −1 or 0 in the switched class and greater values in the conventional than undersized class. Changes were similar between diameter and blood flow in F1 and F2 before deviation. Blood flow in F2 decreased sooner than diameter after deviation indicating that a decrease in vascular perfusion preceded a decrease in diameter. Relationships between F1 and FSH in conventional deviation were similar between waves 1 and 2 for (1) growth rate of F1 on days −1 to 0, (2) interval from emergence of F1 at 4 mm to deviation, and (3) decrease in FSH on days −2 to 0. Relationships between F2 diameter and FSH were dissimilar between classes and between waves 1 and 2 indicating other hormones or factors are also involved in the complex control of F2. For example, the growth rate of F2 was greater (P < 0.05) for conventional than undersized class during wave 1 but similar between classes during wave 2. The FSH surge 2 was similar in profile and prominence between classes but the interval from the FSH peak of surge 2 to deviation was shorter (P < 0.05) in the undersized class (1.5 ± 0.3 d) than in the conventional class (2.3 ± 0.3 d). This was a novel finding and accounted for some of the dissimilarities in growth rate of follicles between classes in wave 2. Results did not support the hypothesis that the extent of blood flow in the wall of future dominant and largest subordinate follicles before deviation is an earlier indicator of follicle destiny than diameter. Results supported the hypothesis that follicle dynamics and FSH concentrations before deviation are temporally associated within conventional and undersized deviation classes but the temporality differs between classes. Highlights • Decrease in blood flow in follicle wall precedes decrease in diameter. • Interval from peak of FSH surge to diameter deviation effects follicle growth. • Differences in FSH surge do not account for differences in diameters. [ABSTRACT FROM AUTHOR]