Anti-oxidative status and semen quality during cooled storage in stallions

Activity of the anti-oxidative enzymes glutathione peroxidase (GSH-Px), superoxide dismutase (SOD) and catalase (CAT), content of thiobarbituric acid reactive substances (TBARS) and SH-groups were determined in native stallion semen (n = 8 stallions). Semen was then diluted in Kenney extender, EquiPro((R)) extender either with or without addition of N-acetyl cysteine or phosphate-buffered saline (PBS) and stored for 72 h at 5 degrees C. Correlations between initial activity of enzymes and development of semen motility and membrane integrity were calculated. Activities of GSH-Px, SOD and CAT immediately after semen collections were 10.0 +/- 0.6 picokatals, 0.40 +/- 0.03 SOD units and 0.70 +/- 0.05 nanokatals/10(6) spermatozoa respectively. TBARS content was 0.06 +/- 0.01 nmol and SH-group content 1.7 +/- 0.5 mmol/10(6) spermatozoa. The loss of motile spermatozoa during storage did not differ between extenders. N-acetyl cysteine had no effect on semen motility and membrane integrity. The loss in membrane-intact spermatozoa was highest (P < 0.05) in semen diluted in PBS. Motility and membrane integrity after addition of extender were positively correlated with GSH-Px and CAT, indicating that anti-oxidative mechanisms contribute to the initial high percentage of motile and membrane-intact spermatozoa. However, in these samples the decrease in semen quality was most pronounced. No correlations existed between initial activity of anti-oxidative enzymes, peroxidation products and semen quality during storage. This indicates that once extender has been added, peroxidative damage to sperm membranes is not the predominant cause of losses in semen quality.