Effects of melatonin on in vitro oocyte maturation and embryo development in pigs

Background and Aim: In vitro fertilization (IVF) efficiency in pigs remains suboptimal, partly due to oxidative stress during oocyte maturation and embryo development. Melatonin (MLT), an endogenous antioxidant, has been proposed as a beneficial supplement in reproductive culture systems. This study aimed to evaluate the effects of different concentrations of MLT on in vitro porcine oocyte maturation and subsequent embryo development. Materials and Methods: Ovaries were obtained from prepubertal gilts at a local slaughterhouse. A total of 1142 cumulus-oocyte-complexes (COC) were allocated into four groups and matured in vitro with 0, 1, 3, or 5 μM MLT for 44 h. Oocyte maturation was assessed using aceto-orcein staining and viability with trypan blue staining. Subsequently, 1312 COC underwent IVF using a standardized sperm concentration, followed by embryo culture in North Carolina State University-23 medium supplemented with corresponding MLT concentrations for 8 days. Embryo development was classified according to cleavage, morula, and early blastocyst stages. Data were analyzed using analysis of variance with Tukey’s post hoc test (p < 0.05). Results: Although supplementation with 1.0 μM MLT resulted in the highest metaphase II oocyte maturation rate (45.9% ± 5.70%) and blastocyst formation (26.9% ± 9.57%), no significant differences were observed among treatments in either oocyte maturation, COC viability, or embryo development stages (p > 0.05). Conclusion: Supplementation with 0–5 μM MLT during oocyte maturation and embryo culture did not significantly enhance in vitro maturation rates or embryonic developmental outcomes in pigs. Further investigations are warranted to optimize MLT concentrations and elucidate its mechanistic role during porcine oocyte and embryo in vitro culture. Keywords: cumulus-oocyte-complexes, embryo development, in vitro maturation, melatonin, pigs.