Relação entre qualidade oocitária, produção in vitro de embriões e características de fertilidade em vacas Brahman e Simental

Abstract

The possible links between antral follicle count (AFC), pre-antral follicle population, breed (Brahman and Simmental), genitalia morphometrics, meiotic progression and embryonic cell count in cows were analyzed. Antral follicle count classes (high: ≥50; intermediate: 30–49 and low: <30) and ovarian volume (OV) large: >11mm³; intermediate: > 8 and ≤ 11mm³ and small: ≤ 8 mm³) were established for analysis. AFC and vulva width (VW) classes were defined separately for Brahman and Simmental cows, respecively as follows; AFC: high (≥50 and ≥25), intermediate (30–49 and 16-24) and low (<30 e ≤15); VW: large (> 123mm and 80 mm), intermediate (> 102mm and ≤ 123mm; > 65mm and ≤ 80mm) and small (≤ 102mm e ≤ 65mm). Data were analyzed using procedures (REG, GLM and GLIMMIX) from SAS® (SAS, Cary, NC- USA). There was a positive correlation (P<0.05) between AFC and the number of normal primordial (r=0.90) and secondary (r=0.53) follicles. Grade I, II and viable oocyte numbers were higher in the high AFC class (7.86±0.6, 4.02±0.39 and 16.26, respectively) compared to the intermediate (4.85±0.67, 2.76±0.43 and 13.05±1.23, respectively) and low (classes (3.27±0.73, 1.24±0.47 and 8.07±1.34, respectively). Mean total AFC was higher (P<0.05) in the large OV class (58.50±3.94) compared to the intermediate (45.39±4.0) and small (31.62±3.94) OV classes. Grade I and viable oocyte means were higher (P<0.05) in the large OV class (6.69±0.72 and 16.12±1.29) and intermediate (6.22±0.74 e 15.03±1.31) compared to the small (3.72±0.72 and 9.37±1.29). Brahman cows had higher (P<0.05) AFC (41.46±2.53 versus 23.27±3.19) and VW (109.41±1.01mm versus 72.29±1.01mm) than Simmental cows. The AFC in the large VW class (44.29±0.87) was superior (P<0.001) compared to the remaining VW classes (intermediate: 35.86±0.75 and small: 27.46±0.69). The number of viable oocytes (17.23±0.41 and 12.15±0.46), total embryos (6.89±0.26 and 2.50±0.21), embryo production efficiency (38.37±0.62 and 22.43±0.62), pregnancy rate (38.40±0.83% and 29.67±0.91%) and the efficiency of viable oocyte in relation to pregnancy (12.61±0.48% and 8.84±0.52%) were higher (P<0.05) in the Brahman compared to the Simmental breed. The proportion of oocytes in metaphase II in the high AFC class (81.20%) was superior (P<0.0001) compared to the intermediate (62.5%) and low (41.51%) AFC classes. The proportion of metaphase I, telophase I and anaphase I oocytes in the intermediate AFC class (26.04%) was superior (P<0.05) in than in the high (8.55%) and low (14.15%) AFC classes. The percentage of germinal vesicle break down oocytes in the low AFC class (32.08%) was higher (P<0.0001) than in the high (5.98%) and intermediate (8.33%) AFC classes. Mean embryo number in the high AFC class (188.37±1.3) was superior (P<0.0001) compared to the intermediate (137.97±1.3) and low (110.33±1.3) AFC classes. It is concluded that antral follicle count, ovarian volume and vulva width are characteristics that may predict oocyte recovery, meiotic progression, in vitro embryo production and embryonic cell count, within the present experimental conditions and perhaps be considered in fertility selection programs.