Cryopreservation of Giraffe Epidydimal Spermatozoa Using Different Extenders and Cryoprotectants

Giraffe sperm can swim again after being frozen. Preserving that ability could make stored sperm useful for moving genes between populations without moving a whole giraffe. The difficulty is that surviving a freeze is not the same as emerging able to move effectively, and earlier giraffe results had been inconsistent.

Robert Hermes, Alexis Lécu and colleagues recovered sperm from seven adult giraffes after independently planned castrations or euthanasia. They divided the samples among three protective liquids, each paired with either glycerol alone or a mixture containing less glycerol and another freezing protectant. The team measured movement, cell structure and membrane function before freezing and after thawing.

The best-performing formulation left about 57% of sperm moving after thawing, including 45% moving progressively forward. Using the mixed protectants improved movement significantly in the two commercial liquids; the improvement in the laboratory-made liquid was smaller and statistically uncertain. Many cells retained functional membranes even when movement was poor, showing why one measure cannot describe the whole outcome. No inseminations were tested, so swimming sperm did not yet mean demonstrated fertility. The experiment nevertheless improved a practical step towards genetic storage: preserving giraffe sperm in a condition potentially useful after the original animal is no longer available.