VI® CONG. INTERN. REPROD. ANIM. INSEM. ARTIF., PARIS, 1968, VOL. II

according to each of the three stallions used was 38 to 63 %
42.9 in total. The conception rate after the first insemi-
nation was 44.2 % in total for the above three tests in {d55
mares.

Table 1. Examples of sperm viability after thawing.
AT e e e I e

Stallion No. of Before After Recovery rate
trials freezing freezing (%)
S e e L O S N e £ e s e
A 26 70-85 65-80 80-100 (94)
B 5 80-90 75-80 80-100 (92)
C 6 65-80 55-70 80-88  (85)
D 2 60-60 50-50 83-83  (83)
E 2 65-70 55=55 79-85 (82)
F 30 80-90 65-70 76-82  (80)
G 5 65-70 35-40 Lkz-57  (50)

e e R e R S
Note: Sperm viability is shown by sperm motility index.
Index was calculated from both % of live sperm
and activity of sperm motility.

Table 2. Conception rate of frozen semen.

e e D e R S et Dt o NS D e O
No. of mares No. of mares Conception
inseminated conceived rate (%)

N e O

Tst testrint 106 2 2 100.0
2nd test in 1966 6 3 50.0
3rd test in 1967 105 Ly L2 .9

Total 113 50 4y 2

e ettt ettt e e e

SUMMARY: The authors examined the factors which seem to be
related to the freezability of spermatozoa. Then they carried
out conception trial with frozen horse spermatozoca. The
collected semen was centrifuged, and a kind of egg yolk buffer-
ed solution was added to the condensed semen. Final glycerol
concentration of 4 to 5 % and glycerol equilibration time of

5 to 5 hours gave the best results. The diluted semen was
poured into slender vinyl straws of one ml capacity and cooled
below -80°C in a few minutes with liquid nitrogen vapor.

The frozen semen was preserved in the liquid nitrogen. The
freezability of horse spermatozoa was much higher than expect-
ed and the recovery rate of sperm motility after thawing was
80 to 100 % in some individuals. The conception rate after
first insemination was 4%4.2 % in 113 mares in total. This
figure is comparable tc the conception rate in artificial
insemination with liquid semen.

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