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 to the station from a 

 region of Arkansas in which purebred bulls had not been used. Then- 

 average milk production was not known but was doubtless much 

 less than that which was obtained from the same cows under careful 



^r fC3jS*<v-« -cif, •:*?:*---t-\ -? {Ka^-l'---^-* 1 - 



Fig. 16.— 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, ma}^ be summarized 

 as follows, after making the proper correction for age: 



Effect of breeding scrub milk cows to purebred bulls. 



Description. 



Cows 



Lactation 



Average 

 pounds 

 milk. 



tested. 



periods. 



5 



15 



3,169 



2 



15 



3,598 



7 



28 



4,036 



13 



40 



5,556 







6 



8,402 



Average 



pounds 



butterfat. 



Scrubs — mature when obtained . . . 

 Scrubs — 4 years old when obtained 



Scrubs — developed at station 



One-half pure blood 



Three-fourths pure blood 



154 

 166 

 191 

 253 

 358 



