Evaluation of alternative cryoprotectants for preserving stallion spermatozoa.

This research article explores alternative cryoprotectants in an effort to better preserve stallion spermatozoa, and found that compounds methyl formamide and dimethyl formamide are as effective as the traditional glycerol for freezing, and potentially cause less osmotic damage to stallion spermatozoa.

Background

• The use of frozen stallion sperm is recognised by many breed registries. However, the limited use of this technique is due to poor fertility results in some stallions, which is believed to stem from the osmotic stress experienced by the sperm when glycerol is used as a cryoprotectant compound during the freezing and thawing processes.

Objective and Methodology

• In order to counteract this, the researchers for this study sought to identify alternative cryoprotectants that may mitigate osmotic damage more effectively than glycerol. Specifically, they looked for cryoprotectants that had lower molecular weights and greater membrane permeability.
• The study involved comparing the motility (ability to move spontaneously and actively) of sperm under different conditions – with different cryoprotectants added to a diluent of skim milk and egg yolk (SMEY). Different concentrations of various amides were used and their results compared to that of glycerol.

Results

• The results suggested that at a concentration of 0.55 M, glycerol generated the highest percentages of motile sperm cells at 61%, compared to other amides like methyl formamide (40%) or dimethyl formamide (38%).
• However, when the concentrations of methyl and dimethyl formamide were increased to between 0.6 and 0.9 M, the motility percentages of cells rose to similar values as that seen with glycerol.
• Additionally, the replacement of glucose and fructose with either raffinose or trehalose in the SMEY diluent did not increase the motility percentage of sperm cells. The addition of methyl cellulose also showed no improvement in sperm motility post cryopreservation.

Conclusion

• The study concluded that both methyl formamide and dimethyl formamide protected stallion sperm equally effectively as glycerol during cryopreservation. As these compounds permeate the plasma membrane more effectively than glycerol, it is suggested they would cause less osmotic damage to the sperm cells.
• These findings suggest methyl and dimethyl formamide may prove more effective in preserving stallion sperm, particularly for those stallions that produce sperm with poor post-thaw characteristics when glycerol is used.