Collection, preservation, and assessment of canine epididymal semen - current knowledge and future challenges

Epididymal spermatozoa have great potential as an alternative source of canine germ cells for the preservation of the unique features of both endangered canid species and purebred dogs. Epididymal semen collected from exceptional individuals is usually cryopreserved and constitutes the final reserve of desired biological material. Cryopreservation of semen recovered from the epididymis poses difficulties related to obtaining samples at sufficient concentrations, in addition to its lower cryotolerance than ejaculated semen. Meeting the challenges associated with the conservation of epididymal sperm necessitates delving deeper into the available methods for its acquisition and preservation, in addition to applying appropriate evaluation methods. The quality of cryopreserved epididymal sperm can be influenced by a number of factors, from the collection technique applied to the insemination process utilized. Furthermore, our review provides a comparison of the effectiveness of selected extenders and their supplements and highlights aspects that require improvements or further investigation. The analyzed literature data show that squeezing and retrograde flushing technique of obtaining semen from the epididymis minimizes tissue and erythrocytes contamination. In order to ensure the best quality of epididymal semen after thawing, storage in 4-5 degrees C should be avoided for longer than: 24 h in 0.9% saline or 5 days in chilling extenders. We concluded that the egg yolk based extenders and Bovimix (R) are the most efficient methods of cryopreservation of canine epididymal sperm, however the use of supplementation such as antioxidants requires further investigation.