212 MARKET DAIRYING 
change from one breed to another, is attended with con- 
siderable expense as well as with a certain amount of 
danger. There is always the risk of introducing disease 
into the herd where changes of this kind are made. 
One of the great drawbacks to the gallon or hundred- 
weight basis, therefore, is the handicap which it places 
upon herd improvement. It is now almost universally 
conceded that weighing and testing the milk from each 
cow individually is one of the greatest aids in building 
up a dairy herd. Where milk is sold by weight alone, 
half the benefits of this system are lost to the producer. 
It is possible, for instance, that the most valuable cow in 
the herd, so far as total butter fat production is con- 
cerned, will be found unprofitable to keep if her milk 
yield is low and the quality very rich. There can be 
no satisfactory herd improvement unless the total but- 
ter fat can be taken into account, and this is impractic- 
able when the milk is sold on the quantity basis alone. 
Quality and the Consumer. Wide variations exist 
at present in the quality of market milks. Analyses of 
normal market milks show a variation in fat content of 
from 3% to 5.5%. And there is a great deal of milk 
sold illegally containing only 2.5% butter fat. 
From a nutritive standpoint butter fat is the most 
valuable constituent of milk, but this is not the only 
constituent that varies in market milks. Milk which is 
rich in butter fat is likewise rich in other milk solids, 
such as casein, sugar and albumen; so that the richer 
the milk is in butter fat the richer it is in solids other 
than fat. For this reason it would not be fair to say 
that 100 pounds of 4.5% milk contains only one pound 
more food material than 100 pounds of 3.5% milk. 
The casein, next to the butter fat, is the most valu- 
