38 BULLETIN 106, U. S. DEPARTMENT OF AGRICULTURE. 
Figure 1 shows graphically the rise and fall of abortion above 
and below the average rate of 12 per cent in herd A from year to 
year. The chart shows three abortion storms in which the per- 
centage of known abortions exceeded 25, the most severe outbreak 
being in 1905, with recorded abortions in 42 per cent of pregnancies. 
In figure 2 it is aimed to show the influence of age as expressed 
by the consecutive number of th^ pregnancy. The general aim 
in the herd has been to breed heifers at 16 to 18 months of age, 
so that the first calving ordinarily means about 2 years old, the 
second 3 years old, etc. 
The intensity of abortion in first pregnancy seems to grow with 
the growth of the herd, while abortion in adult cows seems to decrease 
comparatively. As shown in figure 2, in 1911 the abortions in herd 
A amounted to 44 per cent of first pregnancies, to which abortion 
was confined exclusively for the year. The first pregnancies were 
proportionally the highest in the history of the herd. 
Summary of abortion data in herd A. 
Total number of cows 217 
Total number of pregnancies 645 
Average number of pregnancies per cow 3 
Total number of abortions 78 
Average abortions per annum 3. 5 
Average per cent of abortions per annum 12 
Number of individual cows aborted 71 
Percentage of cows which, have aborted 33 
Number of cows aborting twice 7 
Number of cows aborting twice in succession 4 
Number of cows died or killed after first abortion 10 
Number of years covered 22 
Number of cows in which no abortion occurred 6 
Longest duration in years without abortion 4 
Highest number of consecutive pregnancies without abortion 89 
Among the 217 cows of herd A occur the records of the first three 
or more pregnancies of 80 individuals. Of these 80 animals, 18 
were in the herd in 1905, 2 of which had aborted previously, and 
in one of these (50 per cent) abortion recurred. 
Of the 80 cows in Table 4 of which we have records of the first 
three pregnancies, there were aborting in the first or second preg- 
nancy 20, or 25 per cent; in the third or later pregnancy 18 or 
22.5 per cent; while the number not aborting was 42, or 52.5 per cent. 
The chronological order of abortions in these 80 individuals in 
their third or later pregnancies is shown in Table 5. The figures 
in parenthesis indicate that one animal in a group aborted a second 
time in the number of her pregnancy indicated by the figure. 
