Effect of Repeated Freeze-Thaw Cycles on Survival of Bull Spermatozoa

Abstract

Summary To gain certain information relative to the nature of injury suffered by bull spermatozoa when they are frozen and thawed, the following assumption was evaluated: Immobilization is the sole deleterious consequence of freeze-thawing and its rate is controlled by simple probability relations. Observed per cent motility of spermatozoa in the same sample population exposed to five repeated cycles of freeze-thawing was compared with the predicted (calculated) values for each cycle based upon probability relations. Statistical analysis of results with 78 samples revealed that survival was not controlled by simple probability. Weakening of cells, a deleterious effect other than immobilization, and selection of resistant cells by survival were suggested as other possible factors. Additional experiments confirmed the suggestion that some spermatozoa, although motile after freeze-thawing, are injured or weakened, as shown by their diminished resistance to storage as well as rapid cooling above the freezing temperature. The weakening was shown to occur during freeze-thawing and not as a consequence either of subsequent contact with an extender which had been adversely altered–as by effects of freeze-thawing on its constituents–or by a harmful substance produced in it by spermatozoa killed or immobilized during freeze-thawing.