FIFTY-THIRD ANNUAL CONVENTION 139 



will follow, and they will be of varying degrees of producing 

 ability. 



The evidence seems to point to both parents contribut- 

 ing equally to the inheritance governing the milk and but- 

 terfat producing capacity of their daughter's. But if one 

 parent is homozygous or pure for the hereditary factors 

 determining high production and the other parent is heter- 

 ozygous, or mixed, in its inheritance, then the homozygous 

 parent will have the greater influence on the producing 

 capacity of the daughter; yet this daughter will transmit 

 to a part of her progeny the inheritance for low produc- 

 tion that she may receive from her heterozygous parent. 

 From two heterozygous parents, it is to be expected that the 

 daughters will show a great range in producing capacity 

 from very poor to very good. 



The fact that the percentage of butterfat and the milk 

 yield are inherited independently, at least within limits, 

 and that both the sire and the dam contribute to the inheri- 

 tance of their daughters, governing both milk yield and 

 percentage of butterfat, indicates that improvement in yield 

 of butterfat can be brought about by selection for both 

 milk yield and percentage of butterfat. 



The big problem seems to be to locate the" sire that has 

 inherited only the factors determining a high producing 

 capacity. The degree to which he has inherited these fac- 

 tors can be determined only by testing a large number of 

 his daughters and comparing their records with those of 

 their dams. 



The increasing number of records of daughters and 

 their dams becoming available through the cow-testing as- 

 sociations furnishes a means of calculating the comparative 

 worth of a greater number of sires than has been possible in 

 the past. The 23 sires in this study were given comparative 

 rankings in a new method devised by Mr. Graves. Each sire 

 was ranked in comparison with the others with respect to 

 milk yield of his daughters, average butterfat yield, average 

 increase of milk yield, average increase of butterfat, and 

 the percentage of daughters that were better than their 

 dams in milk and butterfat yield. His comparative value 



