A chemically 'defined' diluent for cryopreservation of bovine spermatozoa

A chemically 'defined' extender for the cryopreservation of bovine spermatozoa was developed using commercially available lecithin as an additive to protect cells against freeze damage. The effectiveness of different media in preventing cryoinjury was evaluated by assessing motion activity immediately post-thaw and after 2 h incubation at 37 degrees C by means of automatic computer image analysis. The extender best suited to maintains swimming activity consisted of the zwitter ion buffer system HEPES-Tris/Citrate (HTC) supplemented with 0.9% lecithin. The effectiveness of this diluent was compared with that of an extender containing egg yolk used routinely in breeding stations. While immediately post-thaw sperm samples frozen in HTC showed a lower motion activity than those preserved in egg yolk diluent, the opposite result was obtained after 2 h incubation at 37 degrees C.