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The Effects of Freezing Bovine Spermatozoa in Extenders Containing Antibacterial Agents

American Foundation for the Study of Genetics, Madison, Wisconsin

ABSTRACT

Investigations in England by Parkes (6, 7), Polge and associates (8, 9, 10, 11, 12), and Smith and Polge (13, 14) have revealed promising new developments in methods for freezing and storing mammalian and avian spermatozoa at –79 ° C. Preliminary breeding experiments (10, 11) have resulted in pregnancies in cattle inseminated with spermatozoa stored as long as 20 weeks at –79 ° C., and calves which appeared to be normal have been produced from frozen semen stored for shorter periods (9). These investigators concluded that the important steps in the procedure are: (a) to allow the semen in yolkcitrate to cool to 5 ° C. from 4 to 6 hours, (b) to add gradually during 30 minutes an equal volume of citrate buffer containing 20 per cent glycerol, (c) to equilibrate the semen and diluent for 12 to 20 hours at 5 ° C., and (d) to cool the preparation slowly from 5 ° C. to –15 ° C. at a rate not to exceed two degrees per minute, although below – 15 ° C. the rate may be more rapid.