. Bulletin of the Department of Agriculture. Agriculture; Agriculture. JTL^'^Lf^. Washington, D. C. December 8, 1920 PRINCIPLES OF LIVESTOCK BREEDING. By Sewall Wright, Senior Animal Husbandman, Animal Husbandry Division. CONTENTS. Evolution of animal breeding 1 Reproduction 2 The cell theory 2 The reproductive cells 3 Sexual maturity 4 Frequency of service 5 The breeding season and oestrous cycle 6 The gestation period 7 Fertility 8 Hybrids 10 The reproductive cells in relation to 11 General considerations 11 Modification of heredity 12 Inheritance of acquired characteristics
. Bulletin of the Department of Agriculture. Agriculture; Agriculture. JTL^'^Lf^. Washington, D. C. December 8, 1920 PRINCIPLES OF LIVESTOCK BREEDING. By Sewall Wright, Senior Animal Husbandman, Animal Husbandry Division. CONTENTS. Evolution of animal breeding 1 Reproduction 2 The cell theory 2 The reproductive cells 3 Sexual maturity 4 Frequency of service 5 The breeding season and oestrous cycle 6 The gestation period 7 Fertility 8 Hybrids 10 The reproductive cells in relation to 11 General considerations 11 Modification of heredity 12 Inheritance of acquired characteristics 13 Telegony 14 Maternal impressions 15 Details of hereditary transmission 15 Blending and alternative inheritance 15 Hereditary units 15 Color and albinism in guinea pigs 16 Mendehan inheritance 18 The chromosomes and heredity. 20 Linkage 20 The determination of sex 23 The normal method 23 Sex-linked inheritance 25 The sex ratio 27 The freemartin 29 Mendelian heredity in livestock 30 Polled cattle 30 Colors of cattle 30 Colors of horses 31 Colors of hogs 32 Mendelian heredity in livestock—Continued. Colors of sheep 33 Colors and comb shape of poultry 33 Heredity of form and function in livestock 34 Relations of theory to practice 34 Equality of inheritance from the sexes 34 Prepotency 34 Variation 36 Fixation of heredity by selection 37 Fixation of heredity by inbreeding "... 37 Isolation of genetic differences by inbreeding. 39 The effect of inbreeding on vigor 40 Crossbreeding 42 The system of breeding 42 The purposes of livestock breeding 42 Uniformity of type- 43 Crossbreeding for the market 44 Improvement 45 Grading up 46 Methods of selection 47 General considerations 47 Individual performance and livestock judg- ing 49 The breeding record 50 Pedigrees 50 The value of purebreds 54 Dairy cattle 54 Quality in meat 57 Breeding and soundness in horses 61 Poultry 62 Satisfaction from pleasing appearance 63 Summary 65 EVOLUTION OF ANIMAL BREEDING. The breeding of domestic
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