Effects of egg yolk level, penetrating cryoprotectant, and pre-freeze cooling rate, on the post-thaw quality of stallion sperm.

The research article investigates how altering the level of egg yolk, cryoprotectant, and the pre-freezing cooling rate can affect the quality of stallion sperm post-thawing.

Objective

The main objective of the research was to determine how the levels of egg yolk (a source of phospholipids), type of cryoprotectant (substances that protect biological tissue from freezing damage), and the pre-freeze cooling rate could influence the quality of stallion sperm after thawing.

Method

• The study was executed in two experiments involving ejaculates from a total of 21 stallions, with varying quality levels of sperm (High, Average and Low).
• The experiment first evaluated the effect of two different extenders (mixtures used to extend the volume of sperm) – egg yolk [20% EY) versus skim-milk plus egg yolk [SM + 2% EY].
• Two different cryoprotectants were used – glycerol (Gly) and glycerol combined with methylformamide (Gly + MF).
• The sperm samples were then cooled from 22° to 5°C using different cooling rates (-0.1, -1 and -5 °C/min) before freezing.

Findings

• The study found that for stallions with High or Average sperm quality, a slower cooling rate usually led to a decrease in sperm quality for the SMEY-based extenders compared to the EY-based extenders. However, the sperm quality of stallions with Low sperm quality were not affected by the experimental conditions.
• In the second part of the study, a faster cooling rate (-5 °C/min) yielded lower sperm quality in the BotuCrio (BC) extenders than in the EY-Gly or EY-Gly + MF extenders. But when a slower cooling rate (-1 °C/min) was used, the sperm quality was similar among these treatments.

Conclusion

Based on the findings, the phospholipid levels in the freezing extenders and the pre-freeze cooling rate significantly affect the post-thaw sperm quality of stallions, while the type of penetrating cryoprotectant does not have a noticeable effect on post-thaw sperm quality.