Vle CONG. INTERN. REPROD. ANIM. INSEM. ARTIF., PARIS, 1968, VOL. Il

after freezing. Only in the frozen-thawed samples stored at SOC for
11 days, was DNA content lowered more than the unfrozen one stored at
same conditions. This is regarded as a suggestion of some influence
by freezing and thawing on DNA, but more supplementary experiments
would be needed for the confirmation of this tendency.

When bull semen was preserved at 5°C after dilution with yolk-
citrate, a time-related decrease was observed in the DNA content of
spermatozoa, but there seems no report which 1nvest1gated quantitative
variation of DNA in sperm during storage in frozen state. On the
physico- chemical nature of DNA after freezing at - 196°C, Shikama (
1965) and Bonadonna et al (1966) observed little destructlon of ext-
racted DNA from thymus and sperm, respectively. Salisbury et al (196L)
reported the constancy of DNA content in spermatozoa when smeared
semen was stored at - 25° C, and Hanada, Hiroe and Tomizuka (1965
observed the same result after cold shock of semen with dry ice.

Since the results obtained with storage time changed little, it
could be considered that the DNA content in spermatozoa is stable
during preservation in the frozen state.

The effect of freezing and thawing was shown in the samples sto-
red at 5°C for 11 days, but in the samples stored for 3 days, which
was important from a practical standpoint, no difference was observed
from the unfrozen sample. Usually, there were observed rapid fall in
fertility of sperm after freezing and thawing, and the cause of this
phenomenom seems to relate with other factors than DNA,

REF ERENCES
BONADONNA T. & FORNAROLI D, 1966. Zootecn. e Vet., 21 : 9-10 3 20L-

206,

HANADA A., HIROE K, & TOMIZUKA T. 1965. Jap. J. Anim. Reprod., 11 :
91-9L.
NAGASE H, & NIWA T. 196L. Vth Internat. Congr. Anim. Reprod. &

Artificial Insemination, L : L10-L15,

SALISBURY G.W., LODGE J.R. & BAKER F,N. 196L. J. Dairy Sci., L7 3 165

-168'

SHIKAMA K, 1965. Nature, 207 : 529-530.

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