Effect of different freezing rates and thawing temperatures on cryosurvival of dromedary camel spermatozoa.

The objective of this study was to evaluate the effect of different freezing rates and thawing temperatures on the post-thaw quality of camel spermatozoa. Ten ejaculates from five male camels were frozen at five different freezing rates, achieved by placing the straws at specific heights above the surface of liquid nitrogen for different lengths of time (4 cm for 15 min; 1 cm for 15 min; 7 cm for 15 min; 7 cm for 5 min + 4 cm for 3 min; 4 cm for 5 min + 1 cm for 3 min) followed by storage in liquid nitrogen. Two thawing temperatures (37° for 30 s and 60 °C for 10 s) were subsequently tested. Post-thawing, the samples were evaluated for total and progressive motility, kinematics, membrane and acrosome integrity, and membrane functionality (hypoosmotic swelling test) at zero and 1 h post thawing. Total and progressive motility were significantly higher for the fastest freezing rate (at 1 cm) at 0 h (p < 0.01 for both), as were VCL (p < 0.01), VSL (p < 0.05) and STR (p < 0.05). Freezing at 4 cm produced the lowest values of STR compared to other treatments (p < 0.05). At 1 h, no differences in total motility were observed between freezing at 4 cm and 1 cm, both being significantly better than freezing rate 7 cm + 4 cm (p < 0.01). For progressive motility and VSL, only freezing at 1 cm was superior to the 7 cm + 4 cm combination (p < 0.001 and p < 0.05 respectively). Membrane integrity at 1 h was higher for freezing at 7 cm than at 1 cm (p < 0.01). For thawing temperatures, total motility and progressive motility at 0 h and 1 h (p < 0.001), and acrosome integrity at 1 h (p < 0.01) were higher for 60 °C thawing temperature than 37 °C. The kinematics VCL (p < 0.001), VSL and STR (p < 0.01), and VAP (p < 0.05) showed higher values for 60 °C thawing temperature than 37 °C at 0 h. After 1 h, higher values for VSL, VCL and VAP (p < 0.05) were observed for 60 °C than for 37 °C. In conclusion, a fast freezing rate would probably be beneficial for camel semen, and thawing should be conducted at 60 °C.