CHAPTER X. LIVESTOCK AND POULTRY 
Infectious Diseases 
(Tables 20 to 2h) 
Profitable livestock production is of considerable importance 
to the economy of any country. The losses due to diseases of 
animals in various countries of the world run into a high figure, 
and in some countriss are so great that the food supply of animal 
origin is inadequate. Although vigorous efforts are made to keep 
these diseases to a minimum in the United States, the losses are 
still very serious. 
In this country the responsibility for the control of diseases 
of animals rests with the Federal and State livestock sanitary 
officials with the assistance of practicing veterinarians, re= 
search workers, and the livestock “ners themsetvas, 
In the reports to follow an effort has been made to include 
estimates of annual livestock losses at the farm level from all 
causes for the period 192-51, with separate estimates for 
disease-control costs. In general these losses include mortality, 
or death, losses and the even greater morbidity losses due to 
animal sickness. Morbidity causes loss of milk, eggs, wool, meat, 
and hides; loss of work days for horses; loss of feed consumed; 
labor for animal care and handling; loss of offspring not produced 
in some reproduction diseases; and replacement costs. Animal 
diseases also cause the livestock owner inconvenience and expendi- 
tures for which no estimate can be made. 
In Tables 20 to 26, the use of several decimal places in re- 
cording the loss percentages is not intended to indicate a high 
degree of precision in the estimates, but to show the relative 
significance of the diseases listed. No percentage is given 
where the proportionate loss is less than 0.001 percent. 
Virus Diseases of Livestock 
A number of animal diseases are caused by viruses, which are 
so small that they cannot be seen through the ordinary microscope 
and which are capable of passing through filters that retain 
bacteria. 
A number of viruses have been identified which affect different 
species of domestic animals. Some of them affect only one species, 
which makes research investigations very difficult because it 
eliminates the possibility of working with experimental animals. 
Examples of such diseases are infectious anemia of horses, hog 
cholera and vesicular exanthema of swine, and infectious dysentery 
of cattle. Other viruses affect two or more species, frequently 
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