Dextran is an effective alternative to egg yolk and glycerol in feline epididymal sperm cryopreservation

The cryopreservation of epididymal spermatozoa is essential for conserving genetic material from endangered species of high-genetic value males suddenly die. The most effective extenders for cryopreservation contain glycerol and egg yolk as cryoprotective components, but variability in composition, contamination risks, and potential toxicity, make the need to find more effective and safe alternatives crucial. This study evaluated the effectiveness of dextran as a substitute for egg yolk and glycerol in feline epididymal sperm cryopreservation. Spermatozoa collected from 24 domestic tomcats after routine orchiectomy were pooled in 8 samples. Seven TRIS-based extenders were tested on these pools, containing dextran (10,000 or 40,000 MW) with varying glycerol concentrations (0 %, 2.5 %, or 5 %), compared to a conventional TRIS extender (20 % egg yolk, 5 % glycerol). Pre- and post-cryopreservation assessments included sperm kinetics (CASA), flow cytometric sperm integrity and function, and hyaluronan-binding ability. Dextran 10,000 MW extenders resulted in similar (in glycerol-free formulation) or improved (with glycerol) sperm quality compared to the control, with higher post-thaw total and progressive motility and cell function (P < 0.05). Dextran 40,000 MW did not result in a similar improvement. Dextran 10,000 MW is a promising alternative to egg yolk in feline sperm cryopreservation, reducing reliance on animal-derived components and glycerol. These findings support the development of safer, more standardised cryopreservation protocols, with potential applications in endangered felid conservation. Further studies are needed to refine dextran-based extenders for broader use.