Fertilizing Capacity of Bull Spermatozoa after Freezing at −79° C.

Abstract

IN 1949, Polge, Smith and Parkes¹ reported that glycerol had remarkable properties in protecting spermatozoa against the effects of low temperatures. The most promising results were obtained with fowl spermatozoa, which, frozen rapidly to −79° C. (solid carbon dioxide) or −192° C. (liquid air) in 15 per cent glycerol, resumed full motility on thawing. Later, it was found that fowl spermatozoa so treated were capable of effecting fertilization of the egg². Mammalian spermatozoa have proved more refractory. The spermatozoa of several species—rabbit, guinea-pig and horse³, bull and goat⁴—can be revived to show some degree of motility after freezing at −79° C. in 15 per cent glycerol. However, repeated experiments with the rabbit, the only laboratory animal suitable for artificial insemination, have, as yet, resulted in the fertilization of only one egg by spermatozoa so treated³, and early tests with frozen bull spermatozoa carried out at Shinfield were unpromising, though one calf was reported to have been produced⁵.