Discussion - Cold shock of spermatozoa

Abstract

‘Cold shock’ affecting spermatozoa was first discovered in the U.S.S.R. when artificial insemination was being developed in cold climates. It was found that damage, causing loss of motility and fertilizing capacity, was done to the cells if they were rapidly chilled as distinct from being slowly cooled to the same temperature (Milovanov 1934). Chang & Walton (1940) made quantitative assessments of the damage done to ram spermatozoa by comparing the respiratory activities of rapidly and slowly cooled spermatozoa. No damage was done to the cells if the semen was cooled in stages of 5° C with an interval of at least 2 h between transference from one stage to another. If the interval between stages was less than 2 h, increasing damage was done as the interval shortened until 85% of respiratory activity was lost if semen at 30° C was dropped into diluent at 1° C so that cooling was immediate. The effect of cold shock on the spermatozoa was, however, not instantaneous and damage could be halted by rewarming; a short exposure to a lower temperature was less harmful than a long exposure. Acclimatization to a lowered temperature was also a slow progressive phenomenon, since avoidance of damage depended not upon the rate of cooling between stages, which was the same for all 5° C changes of temperature, but upon the length of the interval (up to 2 h) which was allowed to elapse between each change. Damage by ‘cold shock’ was increased as the temperature fell. Raising the temperature as quickly as possible from 1 to 37° C did no damage to the spermatozoa. The results of Chang & Walton have been substantially confirmed recently by Ryan and Mayer (see Mayer 1956).