Collections having less than 20 inseminations in a "storage-
time-period" have been excluded.

The statistical material is demontrated in table 1. The figure
above the line gives the average 56 days” non return rate and
the figure below the number of collections (more than 20 inse-
minations each) behind the determination.

The material has been analysed concerning correlation and reg-
ression between non return rate on one hand and storage time
on the other, With consideration to the a priori known signi-
ficant variation in non return rates during various seasons

of the year, the analyses have been made within insemination
periods. In the analyses weighting, taking the number of ob-
servations in consideration, has been undertaken.

The result is demonstrated in table 2. The correlation is in
no case significant and the regression low and unsystematic-—
ally changing over zero from minus to plus.

The conclusion is that in the present material no evidence
can be found for a lowered fertility rate with increasing
storage time.

However, the present material is not at all satisfactory for
final conclusions. It thus should be observed that the biggest
number of observations, giving due influence in the statistical
analyses, is made after comparatively short storage time.

For storage times, practised up to now it can be concluded
that no detrimental effect can be shown. The material does
not allow conclusions for storage over 1-2 years.

Literature

J.W. MacPHERSON, 1956. Fertile bovine semen after three years
storage. J. Amer. Vet. Med. Ass., 129, 416.

J.P. MIXNER, S.H. WIGGINS, 1960. Stored frozen semen fertility.
AT Digesty '8, 19,

J.P. MIXNER, S.H. WIGGINS, 1964. The effects of ageing on the
motility and fertility of frozen bull semen. Proc. Vth Int.
Congress on Animal Reproduction.

L.E.A. ROWSON, 1956, The low temperature preservation of ger-
minal cells. Proc., IIIrd Int. Congress on Animal Reproduction.

D.L. STEWART, 1961, Observations on the fertility of frozen
semen, Proc. IVth Int. Congress on Animal Reproduction.

D.L. STEWART, 1964. Observation on fertility of frozen semen
stored at -79 °C and -196 °C. Proc. Vth Int. Congress on Animal
Reproduction.

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