﻿32 BULLETHSr 1372, U. S. DEPAETMENT OF AGRICULTURE 



the yield of milk and increasing the percentage of butterfat, or he 

 may be prepotent in either raising or lowering both the milk yield 

 and the percentage of butterfat. 



This ability of the 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 is homozygous for dominant 

 factors that will determine high milk yield and high percentage of 

 butterfat, he will be prepotent in impressing these characters on his 

 offspring. If he and the dams he is mated with are heterozygous for 

 these factors, as most sires and dams are, a variety of combinations 

 in the different offspring will follow, and they will be of varying 

 degrees of producing ability. 



5. The percentage of butterfat and the milk yield seem to be 

 inherited independently in Holstein-Friesian cattle. This is contrary 

 to the findings of other investigators. The theory generally accepted 

 is that, as the milk yield increases, there will be a decrease in the 

 percentage of butterfat. Though this study showed that in the 

 majority of cases there was a tendency toward a negative correlation, 

 there was a sufficient number showing a tendency toward a positive 

 correlation to indicate that the two are independent of each other. 

 It is also shown that it is possible for a sire to increase both the milk 

 yield and the percentage of butterfat of his daughters. 



6. A great sire of production is one whose daughters have a high 

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

 and butterfat yield over the yield of their dams, and a high percentage 

 of their number better than their dams. All these things must be 

 considered. No one of them alone offers sufficient evidence of the 

 sire's worth. The production of each sire's daughters must be con- 

 sidered in comparison with the production of other sires' daughters. 

 Provided a sufficient number of tested daughters are available for 

 each sire the ranking system shown in this bulletin seems to indicate 

 the comparative merit of the sires in a group. 



7. The production records of the dams of the 10 highest-ranking 

 sires average higher than the records of the dams of the 10 lowest- 

 ranking sires. In neither of these cases, however, does the rank of 

 the sire follow the size of the record of his dam. 



8. Six of the 10 highest-ranking sires and 6 of the 10 lowest-ranking 

 sires are classed as outbred. This seems to indicate that the mere 

 fact that an individual, his sire, or his dam, is line bred, inbred, or 

 outbred is not indicative of the prepotency of that individual for 

 high production. 



LITERATURE CITED 



(1) Graves, R. R. A generJogical study of Holstein-Friesian sires. (In un- 



published manuscript.) 



(2) Babcock, E. B., and Clausen, R. E. 1918. Genetics in relation to agri- 



culture. 



(3) Roberts, Elmer. Journal of Agricultural Research, .vol. 14, no. 2. 



(4) Wilson, James. Sci. Proc. Royal Dublin Soc, vol. 12, no. 33. 



(5) Pearson, Karl. Biometrika, vol. 7, no. 4. 



WASHINGTON : GOVERNMENT PRINTING OFFICE : 1926 



