Qualidade e status antioxidante de oócitos recuperados de doadoras bos Taurus x Bos Indicus com alta e baixa contagem de folículos antrais

Abstract

Antral follicle count (AFC) has been associated with female fertility and oocyte quality, possibly related to oxidative status. However, the relationship between AFC and oocyte oxidative status is poorly understood. This study aimed to evaluate the oocyte quality of crossbred cows with high and low AFC, with emphasis on antioxidant status. Twenty-six lactating Holstein-Gir cows (1/2, 3/4, 5/8 and 7/8), primiparous and multiparous, with a milk production of 17.39 ± 8.38 kg/day and 108 ± 36 days in lactation, were used. Within the genetic groups, the cows were classified as low (first and second quartiles) or high AFC (fourth quartile), excluding the third quartile. Subsequently, they were grouped into G1 (1/2 and 5/8 HG: high CFA, n=3; low CFA, n=6) and G2 (3/4 and 7/8 HG: high CFA, n=5; low CFA, n=8). Cumulus-oocyte complexes (COCs) and follicular fluid were obtained by ovum pick-up after synchronization of follicular wave emergence. Viable COCs (grades I and II) were matured in vitro for 22 to 24 h and denuded for analyses of nuclear maturation, apoptosis, mitochondrial activity, and accumulation of reactive oxygen species (ROS). In the follicular fluid, catalase, superoxide dismutase (SOD), and glutathione peroxidase (GPx) activities were evaluated. As expected, animals with high AFC presented more antral follicles compared to those with low: G1 (26.80 ± 3.61 vs. 15.54 ± 1.53; P<0.01) and G2 (24.60 ± 2.53 vs. 11.40 ± 1.04; P<0.001). The number of COCs recovered was higher in G1 compared to G2 (7.56 ± 1.19 vs. 4.62 ± 0.62; P<0.05). There was no difference (P > 0.05) between G1 and G2 regarding the percentage of viable COCs (65.33 ± 5.56 vs. 69.63 ± 7.26), nuclear maturation rates (51.84 ± 6.97 vs. 52.51 ± 7.08) and apoptosis (48.36 ± 10.26 vs. 1.75 ± 156.43). However, the percentage of degenerated COCs was lower in G1 (24.69 ± 3.50 vs. 36.80 ± 4.55%, P < 0.05). Mitochondrial activity was higher in oocytes from cows with low AFC compared to those with high AFC in G1 (19.55 ± 6.17 vs. 7.11 ± 2.76; P<0.05), but did not differ in G2 (16.92 ± 5.44 vs. 13.00 ± 4.07; P>0.05). ROS production was higher in cows with low AFC, both in G1 (38.98 ± 10.59 vs. 5.03 ± 1.67) and G2 (26.52 ± 8.19 vs. 9.00 ± 2.36; P<0.001). In follicular fluid, GPx activity was lower (0.0185 ± 0.0016 vs. 0.0258 ± 0.0018 U/mg protein/mL; P<0.05) and SOD activity tended to be lower (0.2001 ± 0.01598 vs. 0.2427 ± 0.01582 IU/mg protein/mL; P<0.07) in G1 compared to G2, but there was no difference (P>0.05) between cows with high or low AFC. Catalase activity did not differ (P>0.05) between genetic groups or AFC categories. It is concluded that AFC was not associated with the morphological quality of COCs. However, increased mitochondrial activity and/or ROS production without a concomitant increase in the antioxidant activity of the follicular fluid suggests oxidative stress in oocytes from cows with low AFC.