Superoxide dismutase affects the viability of thawed European mouflon (Ovis g. musimon) semen and the heterologous fertilization using both IVF and intracytoplasmatic sperm injection

Abstract

This study evaluated the effects of superoxide dismutase (SOD) on viability and acrosome integrity of European mouflon spermatozoa after cryopreservation and on the fertilization rates of sheep oocytes after IVF or intracytoplasmatic sperm injection (ICSI). Frozen semen was thawed and washed with synthetic oviduct fluid supplemented with 0.6% bovine serum albumin. After centrifugation, the spermatozoa pellet was split into two culture systems: (i) without SOD; and (ii) in the presence of 1500 IU mL-1 SOD. Sperm viability and acrosome integrity were evaluated simultaneously, immediately after thawing and after 3, 6 and 9 h of culture (5% CO2, 39°C, 90% humidity), by incubating sperm with propidium iodide and fluorescein isothiocyanate-labelled Pisum sativum agglutinin. At the same time, sperm were assessed for motility using a standard scoring system (independent operators' observation of sperm) that graded degree of motility (i.e. 1 = immotile to 10 = maximum motility, as observed at the moment of thawing). For IVF, frozen-thawed semen derived from the two culture systems was placed in culture together with in vitro-matured sheep oocytes. For ICSI, semen derived from the same culture systems as that for IVF was used, and incubated for 1 h under standard conditions. The results showed a marked difference (P < 0.01) between the percentages of live spermatozoa in medium with SOD and those obtained in medium alone, after 3, 6 and 9 h of culture. The percentages of intact acrosome spermatozoa were higher in medium with SOD after 6 h (P = 0.05) of culture. Spermatozoa motility decreased significantly in SOD containing medium at 3 and 6 h of culture compared with motility in control medium. Fertilization rates were significantly lower in medium with SOD than in medium alone, whereas in the ICSI system fertilization rates were significantly higher in the presence of SOD. The results indicate that the addition of SOD to the culture media enhances the viability rates and the acrosome integrity of cryopreserved mouflon spermatozoa.