Response of spermatozoa from the emu (Dromaius novaehollandiae) to rapid cooling, hyperosmotic conditions and dimethylacetamide (DMA)

Three experiments conducted to improve the survival of emu sperm during cryopreservation aimed to: (1) minimize chilling injury during the cooling phase; (2) determine the osmotic effects of dimethylacetamide (DMA), sucrose and trehalose; and (3) investigate the timing and nature of cryoprotectant toxicity. We measured sperm membrane integrity, motility, morphology and egg membrane penetration. In Experiment 1, semen diluted 1:1 with a pre-cooled diluent (5 °C) prevented chilling injury. In Experiment 2, semen was diluted with DMA, trehalose or sucrose (300–2400 mOsm/L) in deionized water. Only added DMA decreased the percentage of morphologically normal sperm. The percentage of motile sperm was higher with DMA than with the sugars, but membrane intact sperm were comparable amongst all cryoprotectants. As for the osmotic effects, the percentage of membrane intact sperm decreased with 2400 mOsm/L and sperm motility decreased with 1200–2400 mOsm/L, but sperm morphology was similar at all osmolarities. In Experiment 3, sperm membrane integrity, motility and morphology were comparable at all DMA osmolarities between sperm equilibrated for 0 and 15 min, and remained unchanged after removal of DMA. We conclude that: (a) loss of sperm function during the cooling phase can be avoided by using a diluent maintained at 5 °C; (b) emu spermatozoa tolerate upto 1400 mOsm/L; (c) DMA results in a permanent change in sperm morphology when it is dissolved in deionized water, but does not alter sperm membrane integrity and motility; and (d) equilibration time of sperm with DMA can be less than 10 min.