Effect of conventional and controlled freezing method on the post thaw characteristics of boar spermatozoa

The objective of the present study was to evaluate the effectiveness of conventional, and controlled freezing method adopting three freezing rates 20 °C, 40 °C and 60 °C/min for cryopreservation of boar semen. Sixty sperm-rich fractions of ejaculates from six boars were utilized for freezing of semen with different freezing methods in lactose-egg yolk glycerol extender using 0.5 ml straws. Semen samples were evaluated for sperm motility, live sperm, acrosome integrity, plasma membrane integrity (PMI) by carboxyfluorescein diacetate plus propidium iodide (PI) staining, mitochondrial membrane potential (MMP) by combined JC-1 plus PI staining and lipid peroxidation (LPO) by BODIPY 581/591-C11 probe after equilibration and after freezing. The results revealed that the post thaw sperm motility, live sperm, live intact acrosome and plasma membrane integrity were significantly (p < 0.05) higher in all the three controlled freezing methods (20 °C, 40 °C and 60 °C/min) as compared to that in conventional method. In addition, the controlled freezing methods yielded higher (p > 0.05) mean values of live sperm with high MMP as compared to conventional freezing. However, the post thaw sperm LPO did not influence by difference in freezing methods. No significant difference on the post thaw sperm qualities was recorded among the three controlled freezing rates. All the sperm parameters assessed declined significantly (p < 0.05) after freezing as compared to that after equilibration irrespective of freezing method employed. In conclusion, cryopreservation of boar semen with controlled freezing methods conferred better post thaw sperm quality as compared to conventional method, and the freezing rates of either 20, 40 or 60 °C/min could provide better freezability of boar semen.