﻿14 BUIiETTN 1372, U. S. DEPARTMENT OP AGEICULTtJRE 



limited number of animals, a segregation of factors that will result 

 in the exact reappearance of either of the parental characters. For 

 crosses within a breed, however, there is not the same evidence of 

 intermediate milk flow and percentage fat. The great variation in 

 records between the daughters of a sire, and also the variation between 

 records of the daughters and their dams, do not indicate a blended 

 inheritance of the type shown by crosses between distinct breeds. 



There are several explanations that may be given to account for 

 this great variation in the production capacity of the daughters of a 

 sire: (1) The factors that determine high-producing capacity may be 

 dominant over those determining a low-producing capacity. (2) 

 Each individual sire and dam may have a double nature in its heredi- 

 tary make-up. The dam may be a good producer, because of domi- 

 nant factors for high production received from one parent, but she 

 may also possess recessive factors for low-producing capacity that she 

 received from her other parent; and, consequently, she may transmit 

 to a part of her offspring an inheritance for high-producing capacity 

 and to the other part an inheritance for low-producing capacity. 

 (3) The cumulative or multiple factor hypothesis is based on the 

 theory that quantitative characters are produced by cumulative 

 factors; that is, when a factor is added to another similar factor, the 

 cumulation affects the degree of development of that character. 



WHAT IS A GREAT SIRE OF PRODUCTION? 



Which is the greatest sire of production? Is it (1) one that gets 

 daughters that are as good as their high-producing dams; (2) one 

 that gets daughters that make considerably larger records than 

 good dams; (3) one that gets daughters that make much larger 

 records than their low or medium-producing dams; (4) one that gets 

 daughters with the greatest average increase of milk and butterfat 

 over their dams; (5) one whose daughters have the highest average 

 yield of butterfat and milk regardless of the dam's average; (6) one 

 that has the greatest proportion of his daughters better than their, 

 dams regardless of the amount of the increase; or (7) one that has 

 daughters showing the greatest uniformity of production?. 



If sires were judged solely by the average increase in yield of their 

 daughters over their dams, some sires having only one-third of their 

 daughters better than their dams would appear better than other 

 sires with two-thirds of their daughters better than their dams. 

 Nor can a sire be judged entirely by the number of his daughters that 

 are better than their dams, for if the dams were low producers and 

 the increase of the daughters was small, the sire would not have 

 great merit. 



It seems desirable to take into consideration aU the following 

 factors in judging the comparative merits of several sires: The 

 average yield of their daughters; the average increase in the yield of 

 the daughters over that of their dams; and the number of daughters 

 that were better than their dams. 



The 23 sires studied are given comparative rankings in Table 5 

 with respect to average milk yield of their daughters, average butter- 

 fat yield, average increase of milk, average increase of butterfat, and 

 the percentage of daughters that were better than their dams in 

 milk and in butterfat yield; in the last column is the sum of his 

 rankings in the various classes. 



