Acrosomal ultrastructure of stallion spermatozoa cryopreserved with ethylene glycol using two packaging systems.
Authors: Alvarenga M A, Landim-Alvarenga F C, Moreira R M, Cesarino M M
Journal: Equine veterinary journal
Summary
# Editorial Summary Cryopreservation remains essential for equine breeding programmes, yet protecting sperm ultrastructure during freezing remains challenging; Alvarenga and colleagues investigated whether ethylene glycol could replace glycerol as a cryoprotectant and whether packaging format influenced post-thaw sperm quality in stallion semen. Using transmission electron microscopy to assess acrosomal integrity alongside motility assessment, they compared glycerol (5%), ethylene glycol at two concentrations (5% and 10%), and a combined glycerol/ethylene glycol formulation, then evaluated these cryoprotectants in both 0.5 ml and 4.0 ml straws. Post-thaw motility ranged from 29.25% to 36.5% across treatments, with the 10% ethylene glycol formulation performing significantly worse, whilst acrosomal integrity was particularly compromised across all groups—only 22.5–28% of sperm retained normal acrosomes after freezing—with ultrastructural damage including outer membrane undulation, swelling, and content loss. Critically, semen frozen in 0.5 ml straws demonstrated superior post-thaw motility and acrosomal integrity (26.7% versus 16.0%) compared to 4.0 ml straws, a finding applicable regardless of cryoprotectant choice. For practitioners managing stallion fertility programmes, these results suggest that packaging format significantly influences sperm survival and that ethylene glycol offers equivalent protection to glycerol, though adoption of smaller straw volumes represents a practical, immediately implementable strategy for improving cryopreservation outcomes.
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Practical Takeaways
- •Use 5% ethylene glycol as a viable alternative to glycerol for stallion semen cryopreservation, offering comparable post-thaw motility outcomes
- •Select 0.5 ml straws over 4.0 ml straws when cryopreserving stallion semen to maximize sperm survival and reduce acrosomal damage
- •Expect significant acrosomal ultrastructural damage with any cryoprotectant; post-thaw motility alone does not reflect membrane integrity, which should be evaluated via electron microscopy for critical breeding decisions
Key Findings
- •Ethylene glycol (5% and 10%) demonstrated similar cryoprotective properties to glycerol (5%) for stallion sperm, with post-thaw motility ranging from 29.25–36.5%
- •10% ethylene glycol significantly reduced post-thaw motility (29.25%) compared to 5% ethylene glycol (36.5%, P<0.05)
- •Only 16.0–28.0% of sperm cells retained normal acrosomal integrity after freezing across all cryoprotectant treatments, with acrosomal swelling and membrane undulation as primary ultrastructural damages
- •Freezing stallion semen in 0.5 ml straws resulted in significantly higher post-thaw motility and acrosomal integrity (26.7%) compared to 4.0 ml straws (16.0%, P<0.05)