22 BULLETIN 1352, IT. S. DEPARTMENT OF AGRICULTURE 
shows a difference in favor of the class A animals, or those which 
did not meet the calving requirement of the rules. As before men- 
tioned, there may be some cows in the single-letter class which 
did carry calves 155 days or more but, through neglect of the owner, 
were not changed to class AA. 
Another significant point brought out by this table is that the tax 
of pregnancy seems to grow more severe with advancing age. The 
difference between the two classes for all ages up to 3 years is insig- 
nificant, but from that age on there is a marked divergence between 
the average records for the two classes; and it would appear that, 
while the young animal carries on the function of reproduction 
without its affecting materially her productive capacity, the older 
cows do not stand up so well under this double strain. 
RECENT IMPROVEMENT IN PRODUCTION 
An interesting fact brought out incidentally by this study is the 
noticeable improvement in production records since the beginning 
of 1920, especially in the last thousand records. This is illustrated 
in Figure 1. ALL the animals shown are classed according to age; 
and in each age class an average record is computed for each succes- 
sive group of 1,000 records in the Register of Merit. These averages 
are plotted in solid lines, and the dotted fines represent the average 
record for each age group over the entire period of time. At the top 
of the graph is shown the year in which each block of 1,000 records 
was completed. 
The chart shows that there has been a general improvement in 
all classes, most of which appears in the last 6,000 records. The 
rise is gradual and would seem to indicate that with the increase in 
experience gained by handling test cows the breeders have developed 
better methods of feeding, conditioning, and caring for animals on 
test which have brought about better average records. The effect 
of years of selective breeding for high production is also a force 
working to raise these averages. 
That some such factors have raised the general average of all 
records also helps to account for the fact that the reentry records 
made after a lapse oi six years or more usually show a larger increase 
due to development than those made after a shorter interval. We 
have here a combination of development of the cows and methods 
of caring for them. 
SUMMARY AND CONCLUSIONS 
Initial advanced-registry Guernsey records and register-of-merit 
Jersey records furnished material for Tables 1 and 2, which show 
the average production for animals grouped according to age. 
A study of these tables shows the actual relationship of average 
records made at different ages. 
The results will be used as a basis for adjusting records of various 
ages in future studies of prepotency of sires made by this bureau. _ 
The age of maximum production for the Jersey cows included in 
this study begins when the cow is 6 years old and continues until 
she reaches the age of 10 y^ years. 
