Antioxidantes na produção in vitro de embriões e criopreservação de sêmen de ovinos

Abstract

In an attempt to diminish the structural damage to the plasma membrane, due to free radicals and reactive oxygen species (ROS), the antioxidants β-mercaptoethanol (BME) and cysteine (CIS) were tested for semen cryopreservation and in vitro maturation (IVM) and culture (IVC) of ovine embryos. Semen samples from four rams of the Crioula Lanada breed were collected with artificial vagina twice weekly (n = 23). Samples of four rams were pooled and split in six treatments: T1, control without antioxidant, T2, with 2mM BME, T3, with 5mM BME, T4, with 2mM BME and 5mM cysteine; T5, with 5 mM BME and 5mM cysteine, and T6 with 5 mM cysteine. Semen was diluted in tris-egg yolk-glycerol and stored in straws of 0.25 mL containing 100 x 106 spermatozoa. Cooling and freezing were performed using a TK3000 and thawing was performed at 37°C for 20 s. Sperm motility, membrane integrity and mitochondrial activity and acrosome, before freezing and after thawing, did not differ between treatments (P> 0.05). Quantification of ROS and total antioxidant activity after thawing were similar between treatments (P> 0.05). At the tested concentrations, the inclusion of BME, and cysteine did not affect sperm viability after thawing. In the first experiment of IVP, the inclusion of 20 mM of BME in IVM and IVC of embryos was compared to a control treatment without antioxidants. There was no deleterious effect of antioxidant on the cleavage rate (control: 70.0%; BME: 69.8%). However, the rate of development to the blastocyst stage with BME (5.2%) was lower (P <0.001) than with the control (16.9%). In the second experiment, we tested the association of 50 mM BME and 600 mM of CIS in IVM and IVC. There was no difference between control and BME/CIS (P> 0.05), for cleavage (60.3% and 64.3%, respectively) and embryonic development rates (33.6% and 36.6 %, respectively). The addition of 20 mM of isolated BME in IVM and IVC sheep embryos was associated with decreased embryonic development to blastocyst. However, the addition of antioxidants BME, and cysteine in combination, did not affect the rates of cleavage and embryo development to blastocyst. Therefore, the combination of antioxidants and CIS BME used in freezing ram semen and PIV, did not improve the treatments that have been added, albeit at different concentrations.