117 INDUCTION OF OVULATION WITH ESTRADIOL BENZOATE AFFECTS THE PROGRESSION OF VASCULARIZATION IN PREOVULATORY FOLLICLES

Abstract

Ovarian changes in blood supply have been related to follicle growth and ovulation in cattle. The aim of the present study was to characterise the vascularization pattern of the preovulatory follicle in cows induced to ovulate with a timed AI (TAI) protocol using oestradiol benzoate. Follicular wave was synchronized in 18 crossbred cows (Holstein × Gir) with the following protocol: Day 0 (D0), insertion of an intravaginal device of progesterone (1 g, P4) and IM injection of oestradiol benzoate (2 mg, EB); D9, intravaginal P4 device was removed and all the animals received IM injections of cloprostenol (0.53 mg) and eCG (300 IU); D10, animals were randomly allocate into 2 groups, which received 1 mL of saline (control group) or 1 mg of EB (EB group). The vascularization of the largest follicle present in the ovaries was evaluated by colour Doppler ultrasonography immediately before treatment (0 h–0 h) and every 6 h thereafter, up to 84 h or until ovulation was detected. The colour Doppler signals present in the follicular wall were subjectively scored on a 1-to-5 scale (1: no or very few blood flow; 5: intense blood flow detected in most of the follicular wall). The colour Doppler evaluations were performed retrospectively using videos recorded at each examination. The interval from treatment to ovulation was compared by Wilcoxon test. Differences in the vascularization score were compared considering the effects of treatment and time using the PROC MIXED procedure of SAS (SAS Institute Inc., Cary, NC, USA). As expected, in cows treated with EB, ovulations tended to occur earlier (48.0 ± 4.5 h v. 54.0 ± 7.1 h; P = 0.055) and were more synchronous (42–54 h, CV of 9.4% v. 42–66 h, CV of 13.3%) than in the control group. In both groups, follicular vascularization score progressively increased (P < 0.001) until ovulation. However, the vascularization score was lower (P < 0.05) in the EB group than in the control group during the 48-h period before ovulation (overall mean of 2.5 ± 0.7 and 3.0 ± 0.6, respectively); consequently, follicles of cows treated with EB ovulated with a lower vascularization score than did those in the control group (3.6 ± 0.5 v. 4.0 ± 0.5, respectively). Four cows (2 of each group) did not ovulate; follicle vascularization score in these cows remained below 2 during all the evaluation period. In conclusion, although an increase in blood flow is required for ovulation, EB-induced ovulations will occur and are associated with a reduced follicle vascularization. This difference may be related to the smaller interval from treatment to ovulation.

Embrapa, CNPq, and Fapemig (CVZ PPM 0067/11) are acknowledged.