Individual variability in post-thaw sperm survival in a captive koala population.
This study documented the extent of individual animal variation with respect to two proven methods of sperm cryopreservation in a captive population of 22 koalas. Semen samples were collected by electroejaculation, diluted in Tris-citrate glucose and equilibrated to 4 degrees C before being further diluted and frozen in media containing a final concentration of either 14% (v/v) glycerol or 12.5% (v/v) dimethylacetamide (DMA). There were significant differences in post-thaw survival of spermatozoa from different animals that were independent of pre-freeze semen quality. Glycerol proved to be a better cryoprotectant than DMA in terms of maintaining motility, plasma membrane integrity and high mitochondrial membrane potential; however, there was no difference between cryoprotectants with regards to their ability to prevent chromatin relaxation. While a positive correlation was observed between motility and mitochondrial membrane potential, both before and after cryopreservation, the slopes of the pre-freeze regression lines of these relationships were significantly altered following cryopreservation, suggesting that the efficiency of energy generation by the mitochondria was lowered by the freeze-thaw process. Based on a cluster analysis of the post-thaw semen viability parameters, the koalas in this study could be divided into two distinct groups; Cluster 1 had significantly higher sperm viability compared to the other cluster, regardless of the cryoprotectant used. The unpredictability of assessing post-thaw survival from pre-freeze koala semen parameters requires further investigation but is likely to be associated with variation in ejaculate composition or inherent genetic differences between animals.
School of Animal Studies, The University of Queensland, Qld., Australia. y.zee@uq.edu.au
Yeng Peng
YP
Zee
William V
WV
Holt
Vere
V
Nicolson
Michael
M
Pyne
Stephen D
SD
Johnston
D000255:Adenosine Triphosphate / Q000737:chemistry; D000818:Animals; D016000:Cluster Analysis; D015925:Cryopreservation; D003451:Cryoprotective Agents / Q000494:pharmacology; D014644:Genetic Variation; D005990:Glycerol / Q000737:chemistry; D008297:Male; D008564:Membrane Potentials; D008928:Mitochondria / Q000378:metabolism; D048368:Phascolarctidae; D055101:Semen Analysis / Q000379:methods; D012662:Semen Preservation / Q000379:methods*; D013094:Spermatozoa / Q000378:metabolism*; D013696:Temperature
D003451:Cryoprotective Agents; D000255:Adenosine Triphosphate; D005990:Glycerol