SELECTION AND IMPROVEMENT OF DAIRY CATTLE 71 



am i ually . It is not at all uncommon to find even greater 

 .differences than this in actual practice. 



The first cross of improved blood makes the offspring one- 

 hal ', the second, three-fourths, the third, seven-eighths of 

 the same blood as the improved breed. The continued use 

 of pure-bred sires of the same breed for 10 to 15 years will 

 change a scrub herd until it will have essentially the same 

 characteristics as the improved breed. The careful breeder 

 gives a great deal of thought to the selection of the sire for 

 his herd. The more skilled the breeder, the greater the care 

 taken in this respect. Almost any pure-bred bull will im- 

 prove a scrub herd, but only the bull of the best inheritance 

 wi'l increase or even maintain the standard of a highly de- 

 veloped herd. 



55. Difference in Transmission of Dairy Qualities by 

 Different Bulls. There is a wide variation in the way 

 dii'ferent bulls transmit dairy qualities. This fact is 

 illustrated by the data in Table 13, compiled by the author 

 from the records of the Jersey herd owned by the University 

 of Missouri. This herd is descended from three cows. Com- 

 plete milk and butter-fat records for 21 years make these 

 comparisons possible. The comparisons are made in each case 

 between the production of the daughters of the various sires 

 used and the dam of these daughters. The figure 4381, for 

 example, given as the milk production of the daughters of 

 Missouri Rioter is an average of the production of each 

 daughter which is found in turn by taking the average of all 

 the lactation periods of the particular animal. If in any case 

 the daughter had only three or fewer lactation periods, the 

 comparison is between those and the corresponding periods 

 for the dam. 



