Mink semen studies : ii. freeze-preservation of spermatozoa

Abstract

Individual or pooled samples of mink semen were diluted 5 times with 4 extenders: A) tris, citric acid, sodium citrate, bactopeptone, glycine and fructose; B) A + 25% egg yolk; C) B + 12.5% glycerol; D) C + 25% milk. Semen was processed as described below and the extended samples were filled in straws, rapidly frozen (8-10° C/min) and quickly thawed (37° C). Samples were evaluated before and after freezing by observing % motile spermatozoa. In Experiment 1, extender B was found to be suitable for pre-freeze storage (23 and 4° C) and C and D for storage in liquid nitrogen. In Experiment II, a final concentration of 20% egg yolk and 7.5% glycerol was attained by a 3 stage dilution technique using extender B with C or D and the combined extender designated +C and +D. The post-thaw motility in extender +C and +D was <10 and <15% respectively. In Experiment III, the pre-freeze storage was reduced to less than 2 hr and slow cooling was employed. Under these processing conditions the samples with 25-80% initial motility showed post-thaw motility of 12 and 19% in +C and +D extenders, respectively after 2 hr storage in liquid nitrogen. Analysis of 13 samples with initial motility above 50% increased the above average to 15 and 26$ for +C and +D respectively. Freezing of epididymal spermatozoa which showed initial motility of 81% resulted in post-thaw motility of 50 and 58% in extenders +C and +D respectively. The results suggest that successful freezing of mink spermatozoa showing high initial motility can be accomplished by the procedure used in this study.