Evaluation of seasonal variations of semen freezability in Leccese ram.

The experiment was carried out in Southern Italy (41 degrees N latitude) to examine the effects of seasonal variations of semen freezability in Leccese ram. Semen from five rams, collected every 2 weeks for a whole year, was frozen in straws, using a system based on Tris-fructose egg yolk as extender to constitute semen doses of 100x10(6) spermatozoa. Post-thaw survival and acrosomal status of cells were assessed by dual staining by Hoechst 33258 and FITC-PSA. Three different forms of fluorescence distribution were displayed indicating sperm without acrosome (unstained cells), sperm with damaged acrosome (cells with incomplete fluorescence over the head), sperm with widespread fluorescence (cells completely fluorescent). Motility and kinetic rating at thawing and after 1 and 3h incubation (37 degrees C) were also assessed. Semen frozen in summer and autumn, corresponding to the breeding season, showed the highest (P<0.01) post-thaw survival of spermatozoa (41.7%) and the lowest (P<0.01) incidence of spermatozoa with damaged acrosome. The positive influence of the summer-autumn period was expressed also on motility and kinetic rating of spermatozoa at thawing. The integrity of the acrosomal membrane was positively correlated (P<0.01) with sperm viability before processing (r=0.32) and after thawing (r=0.51). In conclusion, the results show that season exerts a significant influence on semen freezability in Leccese ram, with the best performance occurring the summer and autumn period, corresponding to the reproductive season in temperate zones.