Activities of antioxidant seminal plasma enzymes (SOD, CAT, GPX and GSR) are higher in jackasses than in stallions and are correlated with sperm motility in jackasses.

This study compared the activities of four antioxidant enzymes (superoxide dismutase, SOD; catalase, CAT; glutathione peroxidase, GPX; and glutathione reductase, GSR) in the seminal plasma of stallions and jackasses. Eighteen stallion ejaculates and 24 jack ejaculates were collected through an artificial vagina. Seminal plasma was obtained by several centrifugations at 3000×g and 4 °C for 10 min, and activities of SOD, CAT, GPX and GSR were subsequently determined. We also evaluated whether the collecting season had any influence on the activities of these four enzymes in both stallions and jackasses. Antioxidant capacity of seminal plasma was significantly higher in jackasses than in stallions (mean ± SEM, SOD: 1707.7 ± 195.9 U/mL vs. 231.9 ± 29.6 U/mL; CAT: 9094.7 ± 1292.9 U/L vs.1682.7 ± 525.9 U/L; GPX 845.4 ± 106.0 U/L vs. 469.7 ± 60.3 U/L; GSR: 50.3 ± 5.1 U/L vs. 20.7 ± 4.6 U/L). Furthermore, whereas season had no effect on the activity of these four enzymes in stallions, the activities of CAT and GPX in jack seminal plasma were significantly higher in the summer than in the other seasons. In addition, the activities of SOD and CAT were found to be significantly correlated with the percentages of progressively motile spermatozoa, and with the percentages of linearity and straightness, respectively, in jackasses. In contrast, the activities of these four enzymes were not correlated with sperm quality parameters in stallions. Finally, while SOD, CAT, and GPX activities but not those of GSR were correlated in jackasses, the activities of all four enzymes were correlated each other in stallions. We can thus conclude that the activities of SOD, CAT, GPX and GSR differ between the seminal plasma of stallions and donkeys, and vary between seasons in jackasses.