Influence of Thawing Diluents on Vitality, Acrosome Morphology, Ultrastructure and Enzyme Release of Deep Frozen Roar Spermatozoa*

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Abstract
The present investigation was performed to study the effect of freezing and thawing on boar spermatozoa. Thirty-one ejaculates from four boars were investigated after thawing in three different thawing diluents (seminal plasma, OLEP, isotonic glucose solution). From each ejaculate one sample of 1 × 109 spermatozoa was thawed in each of the thawing diluents. Each sample was examined in a thermoresistance test in which motility was stimulated with caffeine 30 min. and 3 hrs. after thawing. Furthermore, acrosome morphology and ASAT release from the spermatozoa were investigated for each sample. One ejaculate from the two most frequently used boars was examined by electron microscopy after thawing in each of the thawing diluents. Differences in the aspects studied appeared between isotonic glucose solution and the other two thawing diluents in the thermoresistance test, in the response to caffeine stimulation 3 hrs. after thawing and in the amount of ASAT released from the spermatozoa. The influence on the acrosome morphology varied between the thawing diluents, but the acrosomal alterations did not seem to be connected with the damage reflected by the thermoresistance test and by the measurement of extracellular ASAT activity. The ultrastructural investigation showed that all spermatozoa examined had some degree of ultrastructural alteration as compared with freshly ejaculated boar spermatozoa treated in the same way. This alteration could not be related to any of the thawing diluents. Of the various laboratory tests the thermoresistance test and the measurement of ASAT release are suggested to be sensitive indicators of sperm damage during freezing and thawing. These tests might be useful indicators of variations in sensitivity of spermatozoa to the freezing-thawing procedure.