Seasonal variations in the composition of ram seminal plasma and its effect on frozen-thawed ram sperm.

It has been proposed that seminal plasma (SP) in the extender or in post-thaw media can prevent and revert cold-shock damage in cryopreserved ram sperm; however, this was dependent on season. We evaluated sperm parameters from Frisian ram semen incubated for various intervals with SP from all seasons and stored at -18 or -196 degrees C. At both temperatures, SP from autumn or winter increased (P<0.05) sperm motility, whereas no SP, or SP from spring or summer, had no effect. However, neither viability nor membrane or acrosomal status were modified by SP. Thirteen SP proteins were bound to the sperm surface (16.1, 16.7, 17.4, 23.3, 25.2, 27.5, 35.0, 40.0, 49.0, 53.5, 55.5, 61.0, and 86.0kDa). The SP proteins that bound to sperm were affected by season, but not by conservation temperature. Sperm incubated with SP from autumn had increased concentrations of five proteins; two were identified (with specific antibodies) as RSVP14 and RSVP20. In conclusion, SP from autumn and winter improved sperm motility of frozen-thawed ram sperm, and storage of ram SP at -18 or -196 degrees C did not affect protein composition. The SP proteins that bound to the sperm surface may be responsible for sperm membrane stabilization and should be further investigated.