138 ILLINOIS STATE DAIRYMEN'S ASSOCIATION 



DAIRY SIRE'S DAUGHTERS BEST INDEX 

 OF HIS VALUE 



R. R. Graves, Bureau of Dairying, U. S. Dept. of Agriculture 



A great dairy sire is one whose daughters have a high 

 average yield of milk and butterfat, a high average in- 

 crease in milk and butterfat yield over that of their dams, 

 and a high percentage of their number better than their 

 dams. All these things must be taken into consideration 

 when measuring the value of a dairy sire. No one of them 

 alone offers sufficient evidence of the sire's worth. 



In a study of 23 Holstein-Friesian sires, each having 

 six or more tested daughters from tested dams, some con- 

 clusions were arrived at concerning the hereditary trans- 

 mission of production. Some of the sires in the list raised 

 both the milk yield and the percentage of butterfat of their 

 daughters as compared to the production of their dams. 

 Some raised one and lowered the other. Some lowered both. 

 But no one sire raised both the milk and butterfat percent- 

 age of all his daughters, nor did any one sire lower these 

 records of all his daughters. In other words, while the 

 sires evidenced a prepotency for raising or lowering produc- 

 tion, no one sire was completely prepotent. 



The ability of a sire to raise or lower the yield of his 

 daughters does not necessarily have a correlation with the 

 record of his own dam. Rather, the prepotency of a sire 

 seems to depend upon the combination of factors governing 

 the yield of milk and percentage of butterfat that he has 

 inherited from his parents. If he has inherited only factors 

 that will determine high milk yield and high percentage of 

 butterfat, he will be prepotent in impressing these charac- 

 ters on his offspring. If he and the dams with which he 

 is mated have inherited from their parents a mixture of the 

 factors for both low and high production which is often the 

 case, a variety of combinations in the different offspring- 



