14 BULLETT1S T 1372, U. Si DEPARTMENT OF AGKICULTURE 
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 considerabi} 7 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 sues 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 all 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. 
