Stallion sperm freezing with sucrose extenders: A strategy to avoid permeable cryoprotectants

The aim of this study was to assess different concentrations of sucrose-based extenders combined with bovine serum albumin (BSA) as an alternative to stallion sperm cryopreservation with permeable cryoprotectants. Semen samples (n = 16) were collected from six stallions. Sperm was cooled, filled in 0.5 mL straws and frozen in nitrogen vapor. Post-thaw sperm kinetic parameters, plasma and acrosome membrane integrity were statistically compared among treatments. In Experiment 1, extenders containing 1% of BSA and different concentrations of sucrose (mmol/L, M): 0, 50, 100, 250, 350 and 450 mM were compared. Use of sucrose [100 mM (S2)] resulted in greater values for most of the sperm kinetic parameters assessed (P < 0.001). There were no differences for plasma membrane integrity, except for when sucrose was used at 50 and 250 mM concentrations, and plasma membrane integrity was less (P < 0.05) when these concentrations were used than with the other sucrose concentrations. In Experiment 2, the selected sucrose extender (S2) was compared to an extender containing glycerol as permeable cryoprotectant. Use of the S2 extender resulted in a lesser proportion of sperm with denuded-acrosomes (P < 0.05) in comparison to use of glycerol and values for several kinetic parameters were also greater (P < 0.05) with use of S2. There were no significant differences for the other parameters assessed in this study. In conclusion, stallion sperm can be frozen in the absence of permeable cryoprotectants, using a combination of sucrose 100 mM with BSA-1% as alternative agents.