UNITED STATES DEPARTMENT OF AGRICULTURE 
DEPARTMENT BULLETIN No. 905 
Washington, D. C. ▼ D«,mb„ s, 1920 
B Revised July, 1923 
PRINCIPLES OF LIVESTOCK BREEDING 
By 
SEWALL WRIGHT, Animal Husbandry Division 
Bureau of Animal Industry 
CONTENTS 
Page 
Evolution of Animal Breeding 1 
Reproduction 2 
The Reproductive Cells in Relation lo Heredity 11. 
Details of Hereditary Transmission 15 
The Determination of Sex . 23 
Mendeiian Heredity in Livestock . . . • 30 
Heredity of Form and Function in Livestock 34 
The System of Breeding 42 
Methods of Selection 47 
T.t Value of Purebreds 54 
WASHINGTON 
GOVERNMENT PRINTINC OFFICE 
1923 
