THE EFFECT OF DIFFERENT DILUTION RATES ON POST-THAW QUALITY OF RAM SEMEN FROZEN IN TWO DIFFERENT EGG-YOLK FREE EXTENDERS

The objective of the present study was to evaluate the effects of pre-freezing sperm concentration (200, 400 or 800x10(6) spermatozoa/ml) using two commercial extenders (Bioexcell (R) and Andromed (R)) on post-thaw survival and acrosomal status of ram spermatozoa. Semen samples were obtained from the 5 mature Karayaka rams (aged 2-3 yr) and a total of 30 ejaculates collected from each male twice a week for 3 weeks with the aid of an artificial vagina, during the non-breeding season (February, winter). Semen extended in Bioexcell (R) or Andromed (R) diluents, was loaded into 0.25 ml straws and equilibrated at 4 degrees C for 2 h. Straws were frozen in the vapour of liquid nitrogen and then stored at -196 degrees C. After thawing (at 37 degrees C for 30 sec), sperm motility, acrosomal status and membrane integrity were assessed. Pre-freezing sperm concentration influenced (P<0.001) frezability of spermatozoa and affected all the in vitro parameters at 400x10(6) and 800x10(6) spermatozoa/ml negatively regardless of the extender. Decreasing the sperm concentration into 200x10(6) spermatozoa/ml influenced positively the percentage of sperm motility and membrane integrity extended in Bioexcell (R) (40%, 29%) and Andromed (R) (43%, 32%). The lowest percentage of abnormal acrosome was also described at lowest sperm concentration (200x10(6) spermatozoa/ml) in both extenders as 29 and 26%. It was concluded that significant differences exist between the dilution rates or sperm concentrations. Lower sperm concentrations or higher dilution rates with the commercial extenders were better to protect sperm from damages during cryopreservation.