In-vitro induction of capacitation of fresh and frozen spermatozoa of the Siberian tiger (Panthera tigris).

Electroejaculates from 5 tigers were split and half of each was assayed fresh while the remainder was frozen and thawed before being assayed. Preincubation time, temperature and removal of seminal plasma were evaluated for their effect on in-vitro capacitation. Ability of spermatozoa to penetrate oocytes, as measured by the zona-free hamster egg-sperm penetration assay (SPA), was used as verification of capacitation. Results of the experiments with fresh semen indicate that: (1) preincubation time affects the fertilizability of tiger spermatozoa with 2 h appearing optimal, (2) a preincubation temperature of 37 degrees C results in significantly higher penetration rates than does a 22 degrees C treatment, and (3) tiger seminal plasma does not appear to contain decapacitation factors, as has been reported for several other species. Frozen semen experiments indicate that (1) frozen-thawed tiger spermatozoa must be removed from the environment of the semen extender before capacitation can take place, and (2) the freeze-thaw procedure results in a shortening of the required capacitation time.