Functional capacity and fertilizing longevity of frozen-thawed scimitar-horned oryx (Oryx dammah) spermatozoa in a heterologous in vitro fertilization system

This study was conducted to determine if cryopreservation and thawing reduces the quality of scimitar-horned oryx spermatozoa and thus might be responsible for sub-optimal artificial insemination (Al) efficiency. Functional capacity of frozen-thawed oryx spermatozoa was compared in a heterologous bovine in vitro fertilization (IVF) system after being prepared by four methods. Fertilizing longevity was also assessed after thawing and pre-incubating spermatozoa for 12 or 24 h before IVF. Sperm characteristics (viability, morphology, acrosomal and capacitation status) were superior for samples prepared by Percoll centrifugation and standard swim-up compared with microdrop swim-up and wash methods. Regardless of variation in sperm characteristics over time, fertilization success and embryo development were high and did not differ among treatments. Fertilization and cleavage success for spermatozoa pre-incubated for 12 h before IVF were comparable with that achieved with non-incubated spermatozoa. Even 24 h after thawing, spermatozoa were capable of fertilizing oocytes, but percentage fertilization and embryo cleavage were significantly lower than for spermatozoa pre-incubated for 12 h. Overall, functional capacity of oryx spermatozoa after thawing appears comparable with that of domestic bull spermatozoa. When used for Al, frozen-thawed oryx spermatozoa should be capable of fertilizing oocytes in females ovulating 12 or even 24 h after insemination, providing sperm transport mechanisms are adequate. The functional capacity and fertilizing longevity of oryx sperm after thawing is high, and therefore unlikely to be responsible for decreased Al efficiency in the scimitar-horned oryx.