Cooling rate affects rhesus monkey sperm survival


Stuart Meyers, Department of Anatomy, Physiology, and Cell Biology, School of Veterinary Medicine, University of California, Davis CA 95616, USA.
Tel.: 530-752-9511;
fax: 530-752-7690;


Background  The rate at which lethal intracellular ice formation occurs during cryopreservation is highly dependent on several variables. The objective of this study was to determine the optimal rate at which rhesus sperm can be cooled.

Methods  Experiments were performed using three rates of cooling. Sperm motility was evaluated by computer-assisted semen analysis, and post-thaw viability was determined using propidium iodide labeling and flow cytometry. Semen was frozen at three cooling rates: (i) fast, (ii) slow, and (iii) standard. Straws were thawed for 30 s at 37°C for analysis of motility and viability.

Results  Post-thaw motility and viability were comparable between freezing curves. Sperm cryopreserved using the slow freeze curve exhibited lowest motility and viability.

Conclusions  This study indicates that macaque sperm survive cooling optimally when cooling rates range from −17 to −34°C/minute. Conversely, slow cooling was detrimental and resulted in poor quality sperm.