RESUMEN
Investigations in the past decades have shown that oocytes developmental competence following in vitro fertilization is greatly influenced by an interval between isolation of the ovaries immediately after death/slaughter and oocytes recovery from the visible follicles. In order to determine the optimal conditions for long-term preservation of ovaries, an experiment was conducted with adding different doses of melatonin (0 (C), 500 (M1), 600 (M2), 700 (M3) and 800 (M4) µM) as an antioxidant to sheep ovaries preservation medium (PBS) maintained at 4 and 20 °C for 24 h. The effects on in vitro embryo production (IVEP) parameters including maturation, fertilization, cleavage, and blastocyst rates and the total number of blastomere were evaluated after the ovaries preservation. Melatonin reduced the decline in fertilization rate as an indicator of success in vitro maturation (P ≤ 0.05). Furthermore, ovarian storage time had significant negative effect (P ≤ 0.05) on IVEP parameters. Supplementation with melatonin increased the total cell number of blastocysts as an indicator of embryo quality (i.e. mean blastomeric cells in 4°C groups: 86.00 ± 3.00, 98.50 ± 3.5, 111.5 ± 1.5, 125.5 ± 2.00 and 126.50 ± 5.5 for C, M1, M2, M3 and M4. respectively). Overall, the results showed that the use of melatonin antioxidant in the ovaries storage medium had beneficial effects on sheep oocytes development and embryos quality.