Freezing and Freeze-Drying of Bull Spermatozoa

¹ From the American Foundation for Biological Research, Madison, Wisconsin

The possible dependance of survival upon the time spermatozoa are in contact with the protective substance glycerol, prior to exposure to low temperatures, was investigated. Pretreatment for 5 minutes provided at least as much protection as 18 hours. Microscopic observations on ice formation relative to survival in semen frozen by four different methods, in the presence and absence of glycerol, gave no evidence for the notion that physical injury by ice is the cause of death on freezing and thawing. Site and character of ice formed were preserved by freeze-drying. A study on the effect of rates of cooling on survival revealed that the theory of survival based upon vitrification by rapid cooling does not apply to bull spermatozoa. Spermatozoa in smears of semen on glass slides did not withstand the process of freeze-drying for various periods. Death was attributed to drying and/or reconstitution.