Vie CONG. INTERN. REPROD. ANIM. INSEM. ARTIF., PARIS, 1968, VOL. I

Table 3 shows that fertility was depressed by dilution of
semen and that a further loss occurred on storage of the semen
for 24 hr. at 5 C. This was not matched by the fall in the
motility of the samples or of their viability (84% of spermatozoa
were not stained by congo red nigrosin (5) after chilled storage
in contrast with 927 in samples taken soon after ejaculation).

DISCUSSION. The exact composition of a synthetic diluent for
deep-freezing spermatozoa is determined quite substantially by
the method of processing chosen. Dilution rate, proportion of
seminal plasma in the diluted semen and rate of cooling all
influence survival of deep-frozen ram spermatozoa and singly, or
in combination, interact with components of the diluent.
Preparations made by dialysing and lyophilising milk have
indicated something of the chemical complexity of milk and
have shown how relatively little processing of it will cause
alterations which have detrimental effects on spermatozoa,
However, the addition of small proportions of egg yolk or milk
protein has regularly improved the survival of spermatozoa in
synthetic diluents during chilling or freezing. Having defined
some factors affecting the survival of spermatozoa under
artificial conditions, research at a more fundamental level
is now in progress to study how these substances and processes
alter the structure and biochemistry of the spermatozoon.
Separate insemination experiments have been completed using
milk as a diluent and, generally, lambing rates have been low
after 10- or 20-fold dilution in milk even if the technique of
centrifugation was used to concentrate the spermatozoa into a
small volume for insemination. Apparently changes occur rapidly
after dilution of ram semen which are not grossly damaging
to the motility of the spermatozoa but which seriously affect
their survival, or capacity to fertilise, in the genital tract
of the ewe.

(5) Blackshaw, A,W. 1955. Aust. vet. J. SIIEE2:3 8

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