22 DYNAMIC OF SYNCHRONIZED FOLLICULAR WAVE IN EWES SUBJECTED TO DIFFERENT DOSES OF 17β-OESTRADIOL GIVEN AT THE BEGINNING OF THE PROGESTERONE PROTOCOL

Abstract

This study was designed to evaluate the effect of different doses of 17β-oestradiol injection at the beginning of the progesterone protocol on follicular wave dynamic in ewes. In a random day of the oestrous cycle (D0), twenty-four Santa Ines ewes received an intravaginal progesterone device (CIDR®) and a injection of 17β-oestradiol (E2, Sincrodiol®, Ourofino, Brazil) in different doses (350, 500, and 1000 µg) for G-350E2, G-500E2, and G-1000E2, respectively (n = 8 per group). Ultrasound examinations were performed daily during the CIDR permanence (10 days) using MyLab 30Vet equipment (Esaote, Italy) connected to transrectal linear transducer (frequency of 7.5 MHz). Follicular wave was defined as a follicle or a group of follicles 2 to 3 mm in diameter that grew to ≥4.5 mm in size before regression or ovulation. The day of wave emergence was based on the day on which the largest follicle of a wave was first detected at 2 or 3 mm (retrospective analysis). Data were analysed by ANOVA followed by a Tukey test (mean ± SEM; P < 0.05) using SAS software. The emergence of a new follicular wave after the beginning of protocols was not detected in 8 out of 24 ewes (33.3%), being 3 from G-350E2, 2 from G-500E2, and 3 from G-1000E2. There was difference (abP = 0.04) for follicular wave emergence day (3.00 ± 0.32b, 4.00 ± 0.45ab and 5.20 ± 0.73a) and averaged day of maximal follicle diameter (8.20 ± 0.58b, 9.50 ± 0.34ab and 9.80 ± 0.20a) for G-350E2, G-500E2 , and G-1000E2, respectively. However, the growing period and the maximum diameter of the largest follicle of this wave did not differ between groups (124.80 ± 8.98 h and 5.42 ± 0.25 mm for G-350E2; 132.00 ± 5.37 h and 5.75 ± 0.23 mm for G-500E2; and 110.40 ± 16.28 h and 5.20 ± 0.73 mm for G-1000E2, respectively). In conclusion, the 17β-oestradiol injection at the beginning of the progesterone protocol was not able to induce the emergence of a new follicular wave in all of females, regardless of dose. However, the synchronized follicular wave occurred earlier in females treated with the lowest dose of the 17β-oestradiol than those that received the highest dose. The study received financial support from CNPq and FAPESP.