Fertilizing potential of mouse spermatozoa cryopreserved in a medium containing whole eggs

Experiments were conducted to improve survival of mouse spermatozoa through the cryopreservation process. In the first experiment, percentages of motile spermatozoa and fertilizing capacities of spermatozoa were evaluated when mouse spermatozoa were cryopreserved using three previously reported cryopreservation media: (1) 18% raffinose in 3% skim milk; (2) Tes/Tris medium containing 25% egg yolk and 1.25% glycerol; and (3) PBS containing 18% raffinose and 1.75% glycerol, each at three different cooling rates (-3, -10, and -50 degrees C/min). Spermatozoa frozen in the skim milk/raffinose medium exhibited the highest percentage of motile spermatozoa (39%) when cells were frozen at -10 degrees C/min (P<0.05). The second experiment evaluated the effects of modifying the Tes/Tris/egg yolk medium, comparing different concentrations of egg yolk, BSA, and sodium dodecyl sulfate. Reducing egg yolk from 25% of the medium volume to 5%, increased percentages of motile spermatozoa after cryopreservation from 29 to 36% (P<0.05). Addition of 1% BSA and sodium dodecyl sulfate to medium containing 5% egg yolk further improved percentages of motile spermatozoa after freezing. In the final experiment, 20% whole egg was substituted for 5% egg yolk and 1% BSA used in previous experiments and resulted in percentages of motile spermatozoa (51%) equal to that of the skim milk-raffinose medium. However, fertility rates were higher (68%) than for spermatozoa frozen in the skim milk-raffinose medium (P < 0.05) and were comparable to the fertility rates of fresh spermatozoa (77%; P>0.05). In conclusion, freezing mouse spermatozoa in a medium containing 20% whole egg, 0.035% sodium dodecyl sulfate, and 1.25% glycerol using a cooling rate of -10 degrees C/min preserves the motility and fertilization capacity of mouse spermatozoa.