PRINCIPLES OF LIVESTOCK BREEDING. 
55 
reference. Since, however, it is not possible in most cases to separate 
clearly the effects of grading up from those of better feeding and 
management, it may be well to refer briefly to an experiment recently 
reported by McCandlish, Gillette, and Kildee, of the Iowa agricultural 
experiment station, in which this can be done. 
A number of scrub milk cows were brought t<5 the station from a 
region of Arkansas in which purebred bulls had not been used. Their 
average milk production was not known but was doubtless much 
less than that which was obtained from the same cows under careful 
A Guernsey bull of excellent type. 
management at the station. Five of the cows were mature, 2 were 
4 years old, and 7 either were very young heifers when obtained or 
were born at the station. These scrubs were bred to purebred bulls 
(Holstein, Guernsey, and Jersey), none of which were high priced. 
The records, all made under the same conditions, may be summarized 
as follows, after making the proper correction for age: 
Effect of breeding scrub milk cows to purebred bulls. 
Description. 
Scrubs— mature when obtained . . . 
Scrubs— 4 years old when obtained 
Scrubs — developed at station 
One-half pure blood 
Three-fourths pure blood 
Cows 
tested. 
Lactation 
periods. 
Average 
pounds 
milk. 
3,598 
4,036 
5,556 
8,402 
Average 
pounds 
butterfat. 
154 
166 
191 
253 
358 
