UNITED STATES DEPARTMENT OF AGRICULTURE 
iJEI DEPAR ™ T BULLETIN No. 1352 OB 
Washington, D. C. V 
Augusf, 1925 
EFFECT OF AGE AND DEVELOPMENT ON BUTTERFAT PRODUCTION OF REG- 
ISTER-OF-MERIT JERSEY AND ADVANCED-REGISTER GUERNSEY CATTLE 
By R. R. Graves, Specialist in Dairy Cattle Breeding, and M. H. Fohrman, 
Dairy Husbandman, Bureau of Dairying 
CONTENTS 
The need for more information 1 
Material used in this study 2 
Increasein production with age 2 
The factor of development 5 
Page 
Effect of pregnancy 21 
Recent improvement in production 22 
Summary and conclusions 22 
NEED FOR MORE INFORMATION 
Age and development have a marked influence on the production 
of milk by dairy cows. This fact is acknowledged by the various 
record associations, and the requirements for recognition of cows as 
high producers are adjusted according to the age at which they are 
tested. The register of production is known in the Jersey breed 
as the Kegister of Merit, and in the Guernsey breed as the Advanced 
Register. 
The student of the heredity of productive ability in dairy cattle 
who draws his material from the advanced-register and register-of- 
merit records is confronted with the problem of establishing some 
basis for comparing records made by cows of different ages, so as to 
avoid discrimination against the animal with a record made at an 
immature age. With the vast amount of official testing of dairy 
cattle that has been done there has accumulated a large fund of 
information which is useful and desirable for studies of this character. 
Cows and heifers are tested at various ages. Many animals tested 
as heifers are not re tested after reaching maturity; consequently, 
without some method of adjusting records made at varying ages to 
a comparable basis, the use of this material is greatly restricted. 
The value of a bull is largely based upon his ability to sire heifers 
of uniformly high production. In order to determine the trans- 
mitting ability of a sire, it is necessary to compare the records of his 
daughters with those of their dams. To limit the comparison only 
to those sets of dams and daughters with records at the same age 
47588°— 25f— Bull. 1352 1 
