BACKGROUND Recent studies have noted that the circulating testosterone concentration may affect the ability of sperm to survive cryopreservation. However, few attempts to confirm such a relationship have been made. Wild ruminant species have very marked seasonal changes in their reproductive function and strong annual changes in their plasma testosterone concentration. OBJECTIVES The present work examines the influence of induced changes in testosterone secretion on sperm variables following conventional slow freezing and ultra-rapid freezing, using the Iberian ibex as an experimental model. MATERIALS AND METHODS In a first experiment, testosterone levels were reduced in the middle of the rutting season (December) using the antiandrogen cyproterone acetate (CA). In a second experiment, testosterone levels were increased at end of the rutting season (January) via the use of the androgen testosterone propionate (TP). RESULTS During December, the testosterone concentration was found to be higher in the blood and seminal plasma of untreated males than of CA-treated males (P<0.001 and P<0.05 respectively). Compared to controls, the TP-treated animals had higher blood plasma testosterone concentrations but lower seminal plasma testosterone concentrations during January (P<0.01 and P<0.001 respectively). The seminal vesicles of the TP-treated males were larger than those of untreated males (P<0.05). When CA was administered, sperm viability improved compared to controls (P<0.05), irrespective of the freezing protocol followed. For the ultra-rapid freezing procedure, the cryoresistance ratio for motility decreased when TP was administered (P<0.05). The values for fresh sperm morphometric variables decreased during the 50 days after the end of CA-treatment (P<0.001), and increased over the same time after the end of TP treatment (P<0.001). DISCUSSION AND CONCLUSION The circulating testosterone concentration appears to influence sperm cryoresistance. This may explain the seasonal changes seen in sperm freezability in some species, independent of fresh sperm quality.
Influence of circulating testosterone concentration on sperm cryoresistance: the ibex as an experimental model.