ON INHERITANCE IN THE PRODUCTION OF 
BUTTER FAT. 
By H. L. RIETZ, Ph.D., University of Illinois, Urbana, Illinois, U.S.A. 
(1) Introduction. 
It is the main object of this paper to present an investigation into inheritance 
in the production of butter fat. As far as I am av^^are, no statistical investigation 
has been published dealing with this question, notwithstanding its importance in 
a great industry and also its purely scientific interest. 
Production of butter fat is one of the chief functions of the cow in the service 
of man. We are, in the present paper, concerned with the inheritance of this 
function, which is perhaps highly correlated with certain characters of the organism 
of the cow, but little or nothing is known of the quantitative value of such corre- 
lations. 
The source of the data is the Advanced Register of the Holstein-Friesian 
Association of America. The performance of an individual in the production of 
butter fat is not constant fiom day to day, but varies considerably. The records 
taken from the above register are in pounds of butter fat made in seven consecutive 
days, and are given along with the age of the cow at the time of the test. The 
tests for the register are all made, at present, under the supei'vision of represen- 
tatives of State Agricultural Experiment Stations. In the earlier years of the 
register, certain private tests were accepted. Throughout our work, we have 
taken only records attested by authorized officials of the Association, who are, in 
general, representatives of State Agricultural Experiment Stations. In beginning 
this work over a year ago, there were available 17 volumes representing records 
of 17 successive years and Volume 18 has appeared for use in the latter part of 
the work. However, it turns out that Volumes 1 — 10 give very few pairs of 
variates that satisfy conditions which it seems desirable to impose. For this 
reason, only data from Volumes 11 — 18 are used. 
In the register, a cow often has a record when her dam has none, and in many 
more cases when her granddam has none. This is due in part to the fact that it 
is becoming more fashionable for breeders to enter their cows in the Advanced 
