Most of the semen collected gave a pH of 7.4 10,3 and an osmotic pressure of 290 t |0
milliosmoles. There was always an improvement from 10% - 30% motility with semen and less
clumping after the seminal plasma was removed or when semen was extended. The freeze recov-
ery patterns and storage patterns o semen from four stallions that were frozen around the
year are summarized in Figure |. Excepting for a few exceptions there was a definite drop in
the freezability of stallion semen during the winter months (North America). Semen frozen in
winter was not only poorer in recovery but also deteriorated in storage in liquid nitrogen
demonstrating that sperm cells that survived had suffered latent damage and died in storage.
There is good evidence that stallion semen dies in storage in liquid No if not properly fro-
zen. Semen obtained from stallions of old age and with history of low fertility did not sur-
vive the freeze stress.

Latent damage of freezing of stallion semen was evaluated by storing thawed semen at
55 G

Semen frozen in summer and from known fertile stallions lived for an average of 24 hours
Those frozen in winter and from low fertile stallions did not live for more than a few hours,
some dying within a few minutes. '

Preliminary fertility studies conducted on ten mares resulted in four pregnancies, three
of these giving birth to healthy foals and the fourth still pregnant. The semen used had
been stored from up to a few weeks to a year.

REFERENCES

l. Smith, A. U., and Polge, C. Survival of spermatozoa at low temperatures.
Nature, 166:668. (1950).

2. Szumowski, P. The deep-freezing of stallion semen. Animal Breed. Abstr. 23:124.(1955).

3. Iljinskaja, T. The effect of various factors on stallion spermatozoa frozen to -70°.
Animal Breed. Abstr. 25:132. (1957).

4., Barker, C. A. V. and Gandier, J. C. C. Pregnancy in a mare resulting from frozen
epididymal spermatozoa. Can. J. Comp. Med. 21:47. (1957).

5. Buell, J. R. A method for freezing stallion semen and tests of its fertility.
Vet. Record. 75:900. (1963)

6. Polge, C. and Minotakis, C. Deep freezing of jackass and stallion semen. Vth Inter.
Congress Animal Reprod. Artificial Insemination. 7:545. ()964)

7. Krause, D. and Grove, D. Deep freezing of jackass and stallion semen in concentrated
pellet form. J. Reprod. Fert. [4:139. (1967).

8. Schafner, C. S. Observations o freezing chicken semen. Vth Inter. Cong. Animal
Reprod. 3:426. (1964).

9. King. G. J. and MacPherson, J.W. The effect of glycerol on fertility of liquid boar
semen. A. |. Digest [4:6. (1966).

10. Nishikawa, Y. Studies on reproduction in horses. Published by Japan Racing Association.
(1959).

Il. Rombe S., Kotjagina, V., and Piler, N. An improved method of preserving semen at -79°C.
Animal Breed. Abstr. 33:363. (1965).

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