Vitrification of Iberian wolf (Canis lupus signatus) sperm: A possible alternative to conventional cryopreservation

Equilibration time improves the sperm variables of wild ruminant ejaculated and epididymal sperm cryopreserved by ultra-rapid freezing

This work examines the effect of equilibration time with extender on ultra-rapidly frozen-thawed wild ruminant epididymal (origin: Iberian ibex) and ejaculated (origin: mouflon) sperm variables. Sperm samples were prepared either without prior equilibration, or equilibrated for 30 min before freezing. Higher quality (p < 0.05) frozen-thawed spermatozoa were obtained when equilibration was allowed, for ejaculated sperm in terms of sperm motility, acrosome apical ridge integrity, sperm viability, and percentage of normal cells, and for epididymal sperm in terms of linearity and straightness of sperm movement. The sperm head area, head perimeter, head length and head width were smaller (p < 0.01) in the equilibrated than non-equilibrated frozen-thawed epididymal sperm; no such dimensional changes were recorded for ejaculated sperm. In conclusion, equilibration prior to ultra-rapid freezing improves the cryoresistance of sperm cells, although viable sperm cells can be obtained without equilibration. The epididymal sperm showed greater cryoresistance, supporting the idea that it is more resistant to freeze-thawing than ejaculated sperm.

Epididymal Spermatozoa Show Higher Cryoresistance to Vitrification Process Than Ejaculated Spermatozoa in Dogs

The aim of this study was to investigate differences in the sperm response to a vitrification-warming process between ejaculated and epididymal dog spermatozoa, and to evaluate the efficacy of an animal protein-free extender for vitrification of both types of sperm cells. Vitrified-warmed spermatozoa from the epididymis showed greater (p < 0.001) progressive motility and total motility values than ejaculated spermatozoa, regardless of the diluent. The vitrification procedure returned better results for viability and intact acrosome when human tubal fluid (HTF®) was used (25.10 ± 7.90 and 56.50 ± 6.7, respectively) compared with Tris-Citric acid-Glucose (TCG) (15.20 ± 4.70 and 43.70 ± 7.9, respectively) in ejaculated samples. Similarly, higher total motility (34.5 ± 4.5) was observed in HTF postwarmed samples compared with TCG-treated samples (19.52 ± 5.1). The interaction source (epididymis, ejaculated) × extender had a significant effect (p < 0.001) on the values of total motile spermatozoa after warming. HTF-based extender improved (p < 0.001) total motility values in epididymal samples, but not in ejaculated samples. In conclusion, epididymal spermatozoa show higher cryoresistance to the vitrification process than ejaculated spermatozoa in dogs. The use of HTF is adequate for both ejaculated and epididymal canine sperm vitrification.

DNA integrity and viability of testicular cells from diverse wild species after slow freezing or vitrification

Introduction and objective

Cryopreservation of testicular tissues offers new possibilities to protect endangered species, genetically valuable individuals or even the fertility potential of prepubertal individuals who have died unexpectedly. However, the use of this technique still remains a challenge. In this study, slow freezing and vitrification of testicular tissue was investigated to find out which cryopreservation method could better preserve the viability and DNA integrity of testicular germ cells in diverse wild species.

Methods

Testes were obtained post-mortem from 18 artiodactyls (wild boar, roe deer, dwarf goat, mhor gazelle, European mouflon, African forest buffalo, Malayan tapir, dorcas gazelle, Iberian ibex, gnu, red river hog), 5 primates (colobus monkey, capuchin monkey, mandrill), 8 carnivores (gray wolf, Persian leopard, binturong, European mink, American black bear, suricata), and 2 rodents (Patagonian mara). The testicles belonged to adult individuals and were cut into small pieces and cryopreserved by needle immersed vitrification or uncontrolled slow freezing using a passive cooling device. After warming or thawing, testicular tissues were enzymatically digested and two germ cell types were differentiated based on their morphology: rounded cells (spermatogonia, spermatocytes, and early spermatids) and elongated cells (elongated spermatids and spermatozoa). Cell viability was assessed by SYBR-14/propidium iodide while DNA fragmentation by TUNEL assay with fluorescence microscope.

Results and discussion

Our preliminary results revealed that our uncontrolled slow freezing method better preserved the viability and DNA integrity of elongated cells than vitrification. Such trend was observed in all species, being significant in artiodactyls, carnivores, and primates. Similarly, the viability and DNA integrity of rounded cells was also better maintained in primates by uncontrolled slow freezing, while in carnivores, vitrification by needle immersion showed better results in this type of cells. In artiodactyls and rodents both techniques preserved the viability of rounded cells in a similar manner, although the DNA integrity of these cells was greater after needle immersed vitrification in artiodactyls.

Conclusions

In conclusion, the effectiveness of each cryopreservation method is affected by the phylogenetic diversity between species and cell type.