ABSTRACTS
345
whose ancestry could be traced directly to established English flocks were eligible. The
American association started with only 739 sheep but now registers nearly 20,000
annually.
Two samples of the breed, born in 1925 and 1935 respectively, of 400 animals each,
200 of each sex, were selected for study. Two factors limited the trend of the study :
the recent importation of some foundation stock of these samples and the individual
registration of only the rams in the English flock books. The average inbreeding and
inter se relationship coefficients were determined. These showed that ' about 1.4 per cent
of the heterozygosis which was present in 1911 had been lost by 1925. Similarly
those born in 1935 had lost about 2.9 per cent of the heterozygosis that was present in
1914.' Animals of a particular breed, by reason of their common ancestry, are all
related to each other. Inbreeding results to some extent, therefore, although mating
may be truly at random within that breed. The author states that, ' Under such
circumstances the inbreeding (F) expected purely because of the average inter se re-
lationship (R) would be F=R/2-R.'
The extent of inbreeding found did not explain
the inter se relationships of zero in 1925 and 0.5 per cent in 1935. This was probably
a result of separation into families resulting from geographic separation.
The method of pedigree sampling used made it possible to determine the importance
of various ancestors. Only two animals, both rams, were related to the whole breed as
much as two per cent. Blendworth Herriad, No. 45215, was imported from England.
He was related to the breed to the extent of 2.4 per cent in 1935. This ram's son,
No. C-1659, had a relationship of 3.0 per cent in the same year.
The generation interval was found to be 3.8 years and 3.5 years respectively for
the 1935 and 1925 samples. Dickson and Lush had reported 4.2 years for the Ram-
bouillet breed. The author suggests that the greater this interval the greater the numeri-
cal equilibrium of the breed. [J. N. W.]
Storage of dairy bull spermatozoa. E. W. SWANSON and H. A. HERMAN
(1941). J. Dairy Sci. 24, 7,579
T HE utility of stored or shipped bull semen depends upon the extent to which the origi-
nal fertility of the spermatozoa is retained. The different storage temperatures
and diluents have not provided a solution for all difficulties. The fertility of stored
bull semen has been found to be correlated with the time of survival with vigorous
motility of the spermatozoa. Temperatures of 35° to 40°F. have proved to be the best
for storage if the fresh semen is reduced to such temperatures slowly. The results arising
from the use of diluents have been variable ; most of them increase the volume and may
stimulate motility. The removal of the sperm fluid and concentration of the sperma-
tozoa gave greater survival in storage for horse and boar semen, but not for that of the
bull. For the latter, however, storage without dilution at 40°F. for 12 to 30 hours has
proved the most successful treatment. This paper reconsiders several of these points
with regard to bull semen.
The artificial vagina was used to collect semen from 10 bulls. Motility was rated
from 0 to 5 at 100°F. under 250X magnification. Samples were divided and stored at
40° and 70°F. Motility after 6 hours storage was greater in that stored at 70°F., whereas
after 16 hours the greater motility was found in that stored at 40°F. Samples stored
at 70°F. were all dead after 40 hours while those stored at 40°F. were all alive.
Samples were also diluted with 3 parts of diluents. Three and five per cent glucose
solutions were harmful. Egg-yolk buffer (E. Y. B.) favoured motility up to five days
after which the spermatozoa died rapidly. This effect, however, varied with different
bulls.
Fresh semen was centrifuged at 1300 revolutions per minute for 15 minutes after
which the supernatant fluid was removed with a pipette. The remaining portion
contained a concentration of spermatozoa. Such concentration greatly reduced
motility during the first 48 hours. This was not overcome by replacing the sperm fluid
immediately after eenfcrifugation with Milovanov's S-G-C-2 diluent or 3 per cent
glucose solution ; four volumes of E. Y. B. diluent added at this time, however,
increased motility for four days of storage. Here again the untreated semen survived