Blood flow in the wall of the preovulatory follicle and its relationship to pregnancy establishment in heifers

Color-Doppler ultrasonography was used to compare the vascularity of the preovulatory follicle between heifers that became pregnant compared with nonpregnant. Heifers (n = 34) received a luteolytic dose of PGF2α when the diameter of the largest follicle of the second follicular wave reached ≥11 mm (actual diameter 11.63 ± 0.06 mm). An ovulation-inducing injection of GnRH analogue was given 36 h after the PGF2α treatment. Artificial insemination (AI) was performed 26 h after GnRH treatment, and ovulation occurred in all heifers within 3 h after AI. Follicle blood flow was assessed at Hour 0 (GnRH treatment) and at Hour 26 (AI). Follicle diameter at Hours 0 and 26 was greater (main effect of group; P < 0.03) in the group that became pregnant (n = 25) compared with nonpregnant (n = 9). Percentage of follicle wall with power Doppler signals of blood flow showed an interaction of group-by-hour (P < 0.03), reflecting greater blood flow in the pregnant group than in the nonpregnant group at Hour 26 but not at Hour 0. Spectral-Doppler evaluation of the resistance index for a vessel in the follicle wall resulted in a group-by-hour interaction (P < 0.03) from a lower index in the pregnant group at Hour 26. The lower index indicated greater downstream vascular perfusion in the follicle wall. Results supported the hypothesis of a positive relationship between the extent of blood flow of the preovulatory follicle and successful establishment of pregnancy in cattle.