A comparative study of two cooling protocols on stallion sperm cryosurvival.

This study aimed to compare two different cooling protocols in the preservation of horse sperm and found that cooling to -3°C before freezing doesn’t provide improvement in sperm cryosurvival and its ability to undergo the acrosome reaction.

Objectives and Methods

In the context of horse breeding, the cryopreservation of sperm is a pivotal procedure. However, the methods currently employed produce inconsistent results, often leading to poor sperm survival post freeze-thawing and concomitantly low fertility rates. To potentially improve upon this, this study investigated if a different approach to cooling temperatures prior to freezing would yield better results.

• Study Design: The researchers collected sperm from five stallions and stored them in straws. The sperm was first cooled slowly to +5°C, following which, half the samples were directly frozen while the rest were further cooled to -3°C before freezing. The aim was to compare the effects of the two cooling protocols.
• Evaluation: To discern the effects of the two cooling treatments, the researchers assessed several key parameters post thaw: progressive motility, viability, plasma membrane integrity, acrosome integrity, and capacitation status.

Findings

Upon thawing, the researchers found:

• No difference in motility, viability, acrosome integrity or capacitation status between the two cooling methods. This suggests that cooling to -3°C before freezing had no significant advantage in these regards.
• A statistically significant difference in plasma membrane integrity. The abstract does not specify which cooling treatment yielded better results in this regard.
• Acrosome integrity decreased over time, with or without progesterone incubation, but showed no difference between the two cooling protocols.
• Both capacitated and acrosome-reacted sperm increased as incubation progressed, and exhibited no differences between the cooling treatments, again showing that the -3°C pre-freezing treatment offered no benefits.

Consequently, the study demonstrated that slow cooling to -3°C before freezing did not improve horse sperm cryosurvival or the capability to undergo an acrosome reaction. This suggests that current protocols involving slow cooling to +5°C remain an efficient option for the cryopreservation of horse sperm.