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 (AI) 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 AI,
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 AI efficiency in the scimitar-horned
oryx.
Endometrial injury, the quality of embryos, and blastocyst transfer are the most important prognostic factors for in vitro fertilization success after previous repeated unsuccessful attempts