BULLETIN 281 



STUDIES IN MILK SECRETION 



VII. Transmitting Qualities of Jersey Sires for Milk Yield, 

 Butter-Fat Percentage and Butter-Fat.* 



Raymond Pearl, John W. Gowen and John Rice Miner 



The most important thing which a breeder of dairy cattle 

 desires to know is whether the animals which he breeds are 

 transmitting productive qualities to their offspring. This in- 

 formation is particularly desired for the herd bull since his off- 

 spring are much more numerous than those of the cows and he 

 constitutes one-half the heritage given to them. It would appear 

 beyond doubt or question that if a bull's daughters are on the 

 average poorer milkers, or poorer in the quality of their milk, 

 than the dams from which they came, then the bull is exercis- 

 ing a harmful effect upon the breed. On the other hand, if a 

 bull's daughters are on the average measurably better than, the 

 dams from which they came, in productive qualities, then that 

 bull is exercising a beneficial effect on the breed. Stated in con- 

 crete terms, if D a represents the milk production of a daughter 

 of a given bull and D m the milk production of the dam of this 

 daughter; then the measure of this bull's transmitting qualities 

 for milk production of this pair would be 



Sire's transmitting power=D a — D m 



If the daughter's production is more than the dam's the sign 

 will be plus. The bull is increasing the production of his daugh- 

 ters and consequently furthering the interests of the breed. If 

 the daughter's production is less than her dam's the sign will be 

 minus. The bull is consequently detrimental to the breed. By 

 the summation of these plus and minus differences with regard 

 to sign, the amount and sign of this summed quantity gives the 

 measure of what he did for all his daughters or averaging this 

 difference gives a measure of what he did for each daughter. 



*Papers from the Biological Laboratory, Maine Agricultural Ex- 

 periment Station, No. 128. 





