228 DOMINANT FOLLICLE DEVIATION IN GUZERA BREED (BOS INDICUS) COWS

Abstract

Follicular dynamics of Zebu Cattle are characterized by lower maximum diameter and persistence of dominant follicles, when compared to European breeds. However, the main effects of follicular dominance on subordinated follicle population, and consequently on oocyte recovery and embryo production, have been shown to be similar among breeds. The aim of this study was to evaluate the dominant follicle establishment period, indicated by follicle divergence, in Zebu cows. Pluriparous, non-lactating Guzera breed (Bos indicus) cows (n = 5), presenting a mean body weight of 518.0 ± 48.5 kg and similar body score condition (ranging from 3.5 to 4, in a 1 to 5 scale), were used. In a first trial, follicular dynamics were evaluated daily during 1 (n = 2) or 2 (n = 3) estrous cycles, using a portable ultrasound device equipped with a linear rectal 5 MHz transducer (Aloka SSD500, Aloka Co., Tokyo, Japan). In a second trial, estrous cycles were synchronized using progesterone intravaginal-releasing devices (CIDR, Pharmacia, Sao Paulo, Brazil), and follicular dynamics were evaluated every 6 h after ovulation, during the first follicular wave, until the largest follicle achieved a diameter of 10 mm. During each evaluation ovaries were mapped, and evolution of follicles followed individually. Data are normalized for the moment of follicular divergence, and analyzed by ANOVA. Results are presented as mean ± SD. Data from the first evaluations confirmed the occurrence of cycles with three (4/8) and four (1/8) follicular waves, despite a mean cycle length of 19.1 ± 1.9 days, with a maximum diameter of 11.6 ± 2.4 mm for non-ovulatory follicles, and 14.4 ± 0.5 mm for ovulatory follicles. Follicular deviation during the first follicular wave occurred 49.2 ± 5.0 h after ovulation, when the largest follicle presented a diameter of 7.3 ± 0.6 mm, and the second largest follicle 6.8 ± 0.7 mm. Growth rates of the dominant and the largest subordinated follicles were similar before (0.35 mm/6 h vs. 0.33 mm/6 h, respectively;; P > 0.05), but significantly different after deviation (0.52 mm 6 h v. −0.04 mm 6 h; P < 0.05). These results shows that the lower maximum diameter and persistence of dominant follicles, in Zebu cattle, is partially compensated by an earlier dominant follicle deviation.