LABOR REQUIREMENTS AND MILKING MACHINES. 13 
larger herds when the milking machine is used. Each of these items 
will be considered in detail. 
INTEREST ON INVESTMENT. 
Interest on investment is a widely variable item. When the type 
of milker used is the same, the investment charge per cow is much 
smaller in the large than the small dairies. This is because a power 
plant, piping, etc., have to be installed in the small as well as in the 
large dairy, and the difference in the costs of these equipments is 
not proportional to the number of cows they serve. There is con- 
siderable variation in the costs of the different kinds of mechanical 
milking outfits on the market. The comparatively expensive outfits 
are more frequently used on the farms having larger dairies; there- 
fore, the investment per cow is not as much smaller in these large 
herds as it would appear that it should be. 
COST OF POWER. 
The cost of power per cow falls slightly as the number of cows 
milked increases. The time consumed per cow is greater in a small 
herd than in a large one. 
Power for the operation of milking machines is usually furnished 
by means of a gasoline engine. It does not ordinarily pay to use an 
engine which develops much excess power, as it requires too much 
gasoline. Where it is necessary to pump water this is often done 
at milking time, and a larger engine may be profitably used to do 
the extra work. The cost of power furnished by a gasoline engine 
depends on the local prices of gasoline and oil, and the efficiency 
with which the engine is operated. Electric motors are sometimes 
used as a source of power on farms near large towns where current 
from a power line is available. This form of power is sometimes 
more expensive, but perhaps is more reliable than gasoline. In 
special cases, as, for example, where the herd is large and extra labor 
for emergency hand milking not available, it may sometimes be worth 
the extra investment incurred to have a second gas engine large 
enough to operate the milker, set up in such a manner that in case 
of accident to the engine regularly used it could be pressed into 
service without loss of time. 
The repair costs seem to be greater per cow for the larger herds. 
This is probably due to the fact that with such herds more cows are 
milked with a milking unit than with the smaller herds. The repair 
costs are largely confined to the rubber tubing and rubber linings of 
the teat cups. 
