VIe CONG. INTERN. REPROD. ANIM. INSEM. ARTIF., PARIS, 1968, VOL. Il

Specific studies on the effect of spermatozoan aging on storage at 4265

Two computer sorts of the data were then made to test the valid-
ity of the aging observation. First, the results for all semen used
on Day 4 which had also been used on Days 1,2, and 3 by the same in-
seminators was sorted and an analysis of variance made. These obser-
vations are shown in Table 3. Finally, a similar sort of the fertil-
ity results for semen used on Day 5 which had also been used by the
same inseminators on the preceeding days was made. The results shown
in Tables 3 and 4 have been published (21) and present exactly the
same trends @& earlier shown in the lower left figure for the summated
data. They emphasize that we deal with a realistic event.

Season of the year.

With our relatively warm summers and our cold wintersin the mid-
western United States,the season of the year has influenced fertility
level in the artificial insemination of cattle. Such an influence is
well illustrated in the figure (upper left). The data are for 180-day
nonreturn fertility levels and show the interactions we find between
semen age, through five days of use, as liquid semen stored at 4°C,
and the months of the year. It is the warm months, particularly, which
depress fertility and which increase prenatal losses. Note the re-
markable interaction shown between the length of the storage interval
and the month of the year in which the stored semen was collected.

Effect of individual sires.

Marked differences among breeds (20) and among bulls were found
in each measured characteristic including fertility level measured in
the cow population either at 30 or at 180 days after insemination,the
level of embryonic mortality among bulls, the degree of increase among
bulls in the level of fertility from Day 1 to Day 2, and the negative
slope among bulls for the regression line of fertility on age of se-
men. Some bulls did not show an increase in fertility from Day | to
Day 2. These tended to be the bulls of the highest fertility and
those showing the least decline with aging.

From these observations the conclusion is inescapable that the
fertility and the embryonic loss curves of stored semen are charac-
teristic of the bull producing the semen. Logic dictates that it is
the contained spermatozoa which cause the differences noted. At the
very least these differences among bulls would be the consequence of
the interaction between the genetics of the bull in question and his
lifetime environment. At the extreme the differences in response
among bulls would be due solely to the mean difference among them in
the total gene pools they carry as found reflected in their haploid
gametes.

 

Unfortunately, it is not possible now to determine which of the

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