Spermatozoa of bull, ram, boar, stallion and chinchilla were examined in the electron microscope before and after freezing of samples of semen in liquid nitrogen. The results showed that the ultrastructure of bull spermatozoa was almost identical before and after treatment, but ram and chinchilla spermatozoa showed consistent damage to the outer membrane and acrosome complex. In the ram, damage ranged from slight swelling of the acrosome to total removal of the cytoplasmic regions and most chinchilla spermatozoa were grossly affected. The spermatozoa of boar presented special difficulties at the fixation stage but gross damage to the acrosome was seen. There appeared to be minimal damage to the stallion spermatozoa, although only one sample of this species was examined.
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