COLD SHOCK SUSCEPTIBILITY OF BOAR SPERMATOZOA 529 and

F OUR trials were conducted with boar spermatozoa to determine the effects of dilution rate, seminal plasma content and extender composition on susceptibility to cold shock and the development of resistance to cold during 30 C incubation. Acrosome morphology and sperm motility were used to assess damage by cold shock. The susceptibility of boar spermatozoa to cold shock increased as the dilution rate increased from 1:2 to 1:6 or 1:10. In addition, spermatozoa diluted to 1:6 or 1:10 before incubation were more susceptible to cold shock than spermatozoa diluted 1:2 before incubation and then rediluted to 1:6 or 1:10 after incubation and immediately before cold shock. Spermatozoa that were washed before incubation were more resistant to cold shock after 5-hr. incubation than after i-hr. incubation, indicating that the acquisition of resistance to cold shock during incubation was an inherent property of the spermatozoa. However, seminal plasma provided boar spermatozoa with additional protection against cold shock. The replacement of seminal plasma with Tris-lactose extender containing 2 to 4% casein protected sperm acrosomes against cold shock but did not reduce the adverse effect of cold shock on sperm motility.