Exogenous melatonin improves blastocyst developmental competence and levels of antioxidants in indigenous donor cattle under heat stress

Antioxidative treatment may have a positive impact on improving the blastocyst developmental competence, and may be a possible strategy to mitigate the effects of the heat stress on bovine fertility. The purpose of the present study was to investigate the effects of exogenous melatonin treatment on in vitro blastocyst development rate, levels of antioxidant markers (malondialdehyde, MDA; superoxide dismutase, SOD; glutathione, GSH), steroid hormones, and pregnancy rate in cattle under heat stress. The experiment was conducted in nonlactating indigenous Sahiwal cattle, divided into treatment (n = 25) and control (n = 19) groups. The treatment group received (Day 0) melatonin at 18 mg/50 kg body weight (4 mL) I.M, while the control group received corn oil, 4 mL I.M. On Day 4, all cows were subjected to ovum pickup to aspirate cumulus oocyte complexes for in vitro embryo production. Blood samples (Day 0 and Day 4) were used to determine the concentrations of lipid peroxidation (MDA) and antioxidants (SOD, GSH), and to analyze plasma hormone concentrations. The blastocyst development rate was higher in the treatment group (p < 0.05). The treatment group showed increased (p < 0.05) antioxidant markers (SOD and GSH), plasma melatonin and estradiol concentrations, and decreased (p < 0.05) MDA concentrations in comparison to the controls. The pregnancy rate was non-significantly higher after transferring embryos developed from melatonin-treated group (40 %) than the control group (15.38 %) of cows. The results suggest a potentially beneficial role of exogenous melatonin administration in reducing the impact of heat stress and improving the developmental competence of blastocyst in indigenous cattle.