The influence exerted by natural antioxidants (Vitamin E or sodium asc
orbate) was studied in various thermal treatments of semen and their e
ffect on respiratory activity and membrane integrity during cryopreser
vation. Frozen bovine semen samples of diverse quality were employed i
n the presence and absence of antioxidants. Both in good-quality sampl
es subjected to cold shock and in those of poor-quality standard-coole
d, low superoxide dismutase activity was observed concomitantly with h
igh malondialdehyde production; as regards oxygen uptake there was no
evidence of mitochondrial coupling. In good-quality samples standard-c
ooled in the presence of antioxidants, greater superoxide dismutase ac
tivity, intact acrosome percentage and mitochondrial coupling were rec
orded as well as lower malondialdehyde production than in the controls
. Natural antioxidants would seem to exert a protective effect on the
membrane of the cryopreserved spermatozoon in samples from good-qualit
y semen,