The present study was undertaken to evaluate the effect of trisaccharides supplementation in glycerol-free tris (GFT) for the cryopreservation of dog spermatozoa. In the first experiment (E1), dog spermatozoa were resuspended with 50, 75, 100 or 125 mM of raffinose, melezitose or maltotriose and cooled at 4 ℃ for 10 min. To determine the effect of different cooling time, the spermatozoa resuspended with 100 mM of raffinose, melezitose or maltotriose were cooled during 10, 20, 30 or 40 min at 4 ℃ (second experiment; E2). The straws were then aligned horizontally for 10 min on the rack and then plunged into LN2. In the third experiment (E3), to determine the effect of different vapor freezing time, the spermatozoa resuspended with 100 mM raffinose were cooled at 4 ℃ for 20 min and frozen in LN2 for 5, 10, 15 or 20 min and then plunged into LN2. In the fourth experiment (E4), to compare different freezing methods [cooling plus vapor freezing (CV), cooling plus step-down freezing (CS) and direct step-down freezing (SD)], the spermatozoa resuspended with 100 mM raffinose were cooled for 20 min and frozen in LN2 vapor for 5 min in case of CV method. In case of CS method, spermatozoa were cooled for 20 min at 4℃ and then frozen by the step-down freezing method. The straws were then aligned horizontally at 18, 15, 5, and 2 cm respectively from the surface of LN2 for 1, 1, 1.4, and 5 min, respectively in an L shaped straw holder and then plunged into LN2. For SD method, the straws were directly aligned horizontally at the same levels as CS from the surface of LN2 for 1, 1, 1.9, and 5 min, respectively and then plunged into LN2. After thawing at 37℃ for 25 sec, the spermatozoa were then incubated for 30 min in the freezing extender (E1) or in the 50 mM sucrose supplemented GFT (E2, E3, and E4) at 24℃. Following post-thaw incubation, sperm progressive motility and viability were assessed in E1, E2, E3, and E4. In addition, acrosome integrity, and gene expression related to apoptosis (BAX, BCL2, and Caspase10) and sperm motility (SMCP) were evaluated in E4. The results demonstrated that, in E1, using 75 mM trisaccharides resulted in significantly (p<0.05) higher sperm motility in all sugar groups. Using 100 mM melezitose significantly (p<0.05) improved the post-thaw viability than the 100 mM raffinose. The viability in 100 mM maltotriose was similar with 100 mM raffinose and melezitose group. In E2, the different cooling time has no significant effect on post-thaw sperm progressive motility in all the sugar types. In addition, the viability was variable among the different groups. In E3, liquid nitrogen vapor freezing for 5 min resulted in improved motility and viability. The sperm progressive motility was significantly (p<0.05) higher in CV and SD group compared to CS group and the sperm viability was significantly (p<0.05) higher in CV group compared to the other groups in E4. However, the acrosomal integrity of spermatozoa in the group CV was significantly (p<0.05) higher than the group CS and SD. In addition, the expression of SMCP gene was significantly (p<0.05) higher in the CV group than the CS group. In contrast, the expression of Caspase10 significantly (p<0.05) lower in the group CV and SD than the group CS. Furthermore, the ratio of gene expression of BAX and BCL2 was significantly (p<0.05) lower in the group CV than the group CS. Therefore, cryopreservation of dog spermatozoa in 100 mM of raffinose supplemented GFT cooled for 20 min and vapor freezing for 5 min provides better progressive sperm motility, viability, and acrosome integrity with higher expression of SMCP gene and lower expression of caspase10 and BAX/BCL2 ratio following post-thaw incubation in 50 mM sucrose supplemented GFT for 30 min at 24℃.

In the present study, we evaluated the effect of glucose-fructose and sucrose supplementation in glycerol-free tris (GFT) on sperm motility, viability, ROS level, apoptosis (BAX and BCL2) and motility (SMCP) related gene expression of dog sperm according to different post-thaw incubation time. The spermatozoa collected from five dogs were resuspended (5×107 cell/ml) with GFT containing 86 mM glucose and 86 mM fructose (GF-GFT) or 100 mM sucrose (S-GFT). The sperm (500 μl) were loaded in straws, cooled for 50 min at 4℃, frozen using liquid nitrogen (LN2) vapor for 20 min and plunged in LN2. The progressive motility, viability, ROS (H2O2) level and mRNA expression of spermatozoa were evaluated according to post-thaw incubation time (0 h, 3 h and 6 h) at 24℃. ROS was assessed using H2DCFDA stain by flow cytometry. The relative abundances of BAX, BCL2 and SMCP were assessed using quantitative real-time polymerase chain reaction (RT-PCR). The motility of spermatozoa cryopreserved in GF-GFT was increased throughout the post-thaw incubation time. The motility of spermatozoa cryopreserved in S-GFT was increased at 3 h of post-thaw incubation. Whereas, the sperm ROS level in GF-GFT group was decreased at 6 h of post-thaw incubation. However, the ROS level in the group S-GFT was gradually increased with the progress of post-thaw incubation period. The post-thaw incubation had no substantial effect on mRNA expression of BAX, BCL2 and SMCP genes of dog spermatozoa in both the GF-GFT and S-GFT groups. These results indicate that GF supplementation in GFT improves the progressive sperm motility during the 6 h of post-thaw incubation with maintaining similar sperm viability and is more efficient in reducing ROS after 3 h of post-thaw incubation. The addition of GF in GFT for the cryopreservation of dog spermatozoa and post-thaw incubation would open an option to achieve more functioning spermatozoa for future assisted reproduction practices.

The objective of the present study was to evaluate the effect of disaccharides supplementation in glycerol-free tris (GFT) on dog sperm cryopreservation with respect to pH adjustment of extender and post-thaw incubation. The spermatozoa collected from five dogs were resuspended (5×107 cell/ml) with GFT containing 100 mM of lactose (L), trehalose (T) or sucrose (S) or pH adjusted (6.85) 100 mM of lactose (LP), trehalose (TP) or sucrose (SP). The sperm (500 μl) were loaded in straws, cooled for 50 min at 4℃, frozen using liquid nitrogen (LN2) vapor for 20 min and plunged in LN2. After thawing at 37℃ for 25 s in a water bath, the spermatozoa were incubated at 24℃ for 30 min. The progressive motility, viability, mitochondrial membrane potential (MMP) and mRNA expression of SMCP gene were then assessed. The MMP was evaluated by combined JC-1 plus PI staining. The relative abundance of SMCP was assessed using quantitative real-time polymerase chain reaction (RT-PCR). Adjustment of pH in GFT extender supplemented with disaccharides did not improve sperrm motility and viability. In general, post-thaw incubation increased the progressive motility of spermatozoa. The sperm motility in the group S was significantly (P<0.05) higher than other groups regardless of post-thaw incubation time. Similarly, the sperm viability in the group S was significantly (P<0.05) higher following post-thaw incubation. The higher sperm motility in the group S was also supported with the significantly (P<0.05) higher live sperm having high MMP. There was no significant difference in mRNA expression of SMCP gene among the experimental groups. These results indicate that cryopreservation of dog sperm in GFT supplemented with S and 30 min post-thaw incubation at 24℃ could provide better freezability of dog spermatozoa with improved motility and higher MMP.