The Thai Journal of Veterinary Medicine


The scanning electron microscope features of the zona pellucida of immature porcine oocytes, preserved in hypertonic salt solution, for 7, 14, 28 and 56 days, were compared with the features of fresh immature oocytes. The outer zona pellucida layer showed two principal patterns. The first showed a network, with a spongy appearance and containing numerous pores, while the other had a more compact and smooth structure, with fewer pores. The diameter and the number of outer pores within a 100 μm2 area was evaluated. The mean diameters were 0.55±0.40, 0.47±0.32, 0.42±0.26, 0.40±0.26 for the 7D, 14D, 28D and 56D salt-stored oocytes and 0.42±0.24 μm for the fresh ones. The outer pores of fresh immature oocytes were the widest (p<0.05). The mean number of outer pores (per 100 μm2) were 30.58±7.15, 29.13±4.46, 34.60±1.52, 28.20±5.40 for the 7D, 14D, 28D and 56D salt-stored oocytes and 36.01±9.17 for the fresh ones. There was no significant difference in the mean numbers between the groups of oocytes studied (p>0.05). These results suggest that immature oocytes could be preserved in hypertonic salt solution for 56 days without any change in the morphology of the outer zona pellucida. These preservation techniques can be possibly used during the procedure of oocyte collection in endangered animals and used to determine sperm penetrability in practical experiments.

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