Care and Management of Dairy Cattle 173 
287. Prevention of tuberculosis. — Since tuberculosis is a 
communicable germ disease, it is therefore preventable. If a 
herd is known to be healthy, never bring a new animal into the 
herd until it has been tested, and if there is the slightest suspicion 
that it is tubercular, it should be excluded. 
QUESTIONS 
1. How many dairy cattle are there in the United States? How many 
in your state? In your county? How does your state rank with other 
states in the production of milk and butter? How does your county rank 
with other counties of the state? Name the ten leading dairy states. 
Which state possesses the largest number of cattle to the square mile? 
To the farm? 
2. Why are records of performance essential in herd improvement? 
In breeding, which is the more important, a record of performance or a pedi- 
gree? Are there any cow testing associations in your state? In your 
county? Have they resulted in improvement? 
3. In grading up a herd, when should the surplus calves be disposed of ? 
Which calves should be retained ? 
4. How young should a heifer freshen? What is the average age of 
a milk cow? What percentage of the herd must be replaced each year 
in order to keep the number uniform ? 
5. At what period of life does a cow give her maximum yield of milk? 
Does an old cow give milk with a higher percentage of fat than a young 
one? 
6. In testing milk with a centrifuge tester, why is it that the fat rises 
to the top? Why will milk keep sweet longer at a low temperature than 
at a high? Why does milk sour? Why does pasteurization of milk 
increase its keeping qualities? How do bacteria get into milk? 
7. How is sanitary milk produced? Are there any sanitary farms in 
your county? How much do they get for their product ? 
8. Are there any milking machines in use in your county? How long 
does it take the machine to milk four cows yielding an average of six 
quarts each? Does it milk the animals clean? How long would it take 
.a good hand milker to milk a cow yielding six quarts? Wherein lies the 
