Diseases of poultry

1409
Y. M. Saif TWELFTH EDITION DISEASES OF POULTRY EDITOR-IN-CHIEF ASSOCIATE EDITORS A.M. Fadly J.R. Glisson L.R. McDougald L.K. Nolan D.E. Swayne

Transcript of Diseases of poultry

  1. 1. Y. M. Saif T w e l f t h E d i t i o n Diseasesof Poultry e d i t o r - i n - c h i e f a s s o c i a t e e d i t o r s A.M. Fadly J.R. Glisson L.R. McDougald L.K. Nolan D.E. Swayne
  2. 2. 12th Edition Diseases of Poultry
  3. 3. 12th Edition Diseases of Poultry Editor-in-Chief Y. M. Saif Associate Editors A. M. Fadly J. R. Glisson L. R. McDougald L. K. Nolan D. E. Swayne Editorial Board for the American Association of Avian Pathologists
  4. 4. 1943, 1948, 1952, 1959, 1965, 1972, 1978, 1984, 1991, 1997 Iowa State University Press 2003 Iowa State Press 2008 Blackwell Publishing All rights reserved Blackwell Publishing Professional 2121 State Avenue, Ames, Iowa 50014, USA Orders: 1-800-862-6657 Office: 1-515-292-0140 Fax: 1-515-292-3348 Web site: www.blackwellprofessional.com Blackwell Publishing Ltd 9600 Garsington Road, Oxford OX4 2DQ, UK Tel.: +44 (0)1865 776868 Blackwell Publishing Asia 550 Swanston Street, Carlton, Victoria 3053, Australia Tel.: +61 (0)3 8359 1011 Authorization to photocopy items for internal or personal use, or the internal or personal use of specific clients, is granted by Blackwell Publishing, provided that the base fee is paid directly to the Copyright Clearance Center, 222 Rosewood Drive, Danvers, MA 01923. For those organizations that have been granted a photocopy license by CCC, a separate system of payments has been arranged. The fee code for users of the Transactional Reporting Service is ISBN-13: 978-0-8138-0718-8/2008. First edition, 1943 Second edition, 1948 Third edition, 1952 Fourth edition, 1959 Fifth edition, 1965 Sixth edition, 1972 Seventh edition, 1978 Eighth edition, 1984 Ninth edition, 1991 Tenth edition, 1997 Eleventh edition, 2003 Twelfth edition, 2008 Library of Congress Cataloging-in-Publication Data Diseases of poultry/editor-in-chief, Y.M. Saif ; associate editors, A.M. Fadly ... [et al.].12th ed. p. cm. Includes bibliographical references and index. ISBN-13: 978-0-8138-0718-8 (alk. paper) ISBN-10: 0-8138-0718-2 (alk. paper) 1. PoultryDiseases. I. Saif, Y. M. II. Fadly, A.M. SF995.D69 2008 636.50896-dc22 2007039287 The last digit is the print number: 9 8 7 6 5 4 3 2 1
  5. 5. Dedicated to Dr. H. John Barnes, Associate Editor, Diseases of Poultry, 8th, 9th, 10th and 11th editions
  6. 6. Contributing Authors xi Introduction xix Foreword xxi 01 Principles of Disease Prevention: Diagnosis and Control 3 Introduction, A. J. Bermudez Disease Prevention and Diagnosis, A. J. Bermudez and B. Stewart-Brown Antimicrobial Therapy, D. P. Wages 02 Host Factors for Disease Resistance 47 Introduction, J. M. Sharma Avian Immune System, J. M. Sharma Genetics of Disease Resistance, H. H. Cheng and S. J. Lamont SECTION I: VIRAL DISEASES 03 Newcastle Disease, Other Avian Paramyxoviruses, 75 and Pneumovirus Infections Introduction, D. J. Alexander and D. A. Senne Newcastle Disease, D. J. Alexander and D. A. Senne Avian Metapneumovirus, R. E. Gough and R. C. Jones Avian Paramyxoviruses 29, D. J. Alexander and D. A. Senne 04 Infectious Bronchitis 117 D. Cavanagh and J. Gelb Jr. 05 Laryngotracheitis 137 J. S. Guy and M. Garcia 06 Influenza 153 D. E. Swayne and D. A. Halvorson 07 Infectious Bursal Disease 185 N. Eterradossi and Y. M. Saif 08 Chicken Infectious Anemia Virus and 209 Other Circovirus Infections Introduction, K. A. Schat and L. W. Woods Chicken Infectious Anemia, K. A. Schat and V. L. van Santen Circovirus Infection of Pigeons and Other Avian Species, L. W. Woods and K. S. Latimer 09 Adenovirus Infections 251 Introduction, S. D. Fitzgerald Group I Adenovirus Infections, B. M. Adair and S. D. Fitzgerald Egg Drop Syndrome, B. M. Adair and J. A. Smyth Hemorrhagic Enteritis and Related Infections, F. W. Pierson and S. D. Fitzgerald Quail Bronchitis, W. M. Reed and S. W. Jack 10 Pox 291 D. N. Tripathy and W. M. Reed 11 Reovirus Infections 309 Introduction, R. C. Jones Viral Arthritis, R. C. Jones Other Reovirus Infections, R. C. Jones 12 Viral Enteric Infections 329 Introduction, Y. M. Saif Turkey Coronavirus Enteritis, J. S. Guy Rotavirus Infections, M. S. McNulty and D. L. Reynolds Astrovirus Infections, D. L. Reynolds and S. L. Schultz-Cherry Avian Enterovirus-Like Viruses, J. S. Guy, M. S. McNulty and C. S. Hayhow Turkey Torovirus Infection, D. L. Reynolds and A. Ali 13 Viral Infections of Waterfowl 367 Introduction, P. R. Woolcock Duck Hepatitis, P. R. Woolcock Duck Virus Enteritis (Duck Plague), T. S. Sandhu and S. A. Metwally Hemorrhagic Nephritis Enteritis of Geese (HNEG), J. L. Gurin Parvovirus Infections, R. E. Gough 14 Other Viral Infections 405 Introduction, Y. M. Saif Miscellaneous Herpesvirus Infections, J. P. Duchatel and H. Vindevogel Avian Nephritis, T. Imada Arbovirus Infections, J. S. Guy and M. Malkinson Turkey Viral Hepatitis, J. S. Guy Avian Encephalomyelitis, B. W. Calnek Avian Hepatitis E Virus Infections, X. J. Meng, H. L. Shivaprasad, and C. Payne vii Contents
  7. 7. 15 Neoplastic Diseases 449 Introduction, A. M. Fadly Mareks Disease, K. A. Schat and V. Nair Leukosis/Sarcoma Group, A. M. Fadly and V. Nair Reticuloendotheliosis, A. M. Fadly, G. Zavala and R. L. Witter Dermal Squamous Cell Carcinoma, S. Hafner and M. A. Goodwin Multicentric Histiocytosis, S. Hafner and M. A. Goodwin Other Tumors of Unknown Etiology, R. L. Reece SECTION II: BACTERIAL DISEASES 16 Salmonella Infections 619 Introduction, R. K. Gast Pullorum Disease and Fowl Typhoid, H. L. Shivaprasad and P. A. Barrow Paratyphoid Infections, R. K. Gast Arizonosis, H. L. Shivaprasad 17 Campylobacteriosis 675 Q. Zhang 18 Colibacillosis 691 H. J. Barnes, L. K. Nolan, and J-P Vaillancourt Coliform Cellulitis (Inflammatory Process), J-P Vaillancourt and H. J. Barnes 19 Pasteurellosis and Other Respiratory Bacterial 739 Infections Introduction, J. R. Glisson Fowl Cholera, J. R. Glisson, C. L. Hofacre, and J. P. Christensen Riemerella anatipestifer Infection, T. S. Sandhu Ornithobacterium rhinotracheale Infection, R. P. Chin, P. C. M. van Empel, and H. M. Hafez Bordetellosis (Turkey Coryza), M. W. Jackwood and Y. M. Saif 20 Infectious Coryza and Related Bacterial Infections 789 P. J. Blackall and E. V. Soriano 21 Mycoplasmosis 805 Introduction, S. H. Kleven Mycoplasma gallisepticum Infection, D. H. Ley Mycoplasma meleagridis Infection, R. P. Chin, G. Y. Ghazikhanian, and I. Kempf Mycoplasma synoviae Infection, S. H. Kleven and N. Ferguson-Noel Mycoplasma iowae Infection, J. M. Bradbury and S. H. Kleven Other Mycoplasmal Infections, S. H. Kleven and N. Ferguson-Noel 22 Clostridial Diseases 865 Introduction, H. J. Barnes Ulcerative Enteritis (Quail Disease), D. P. Wages Necrotic Enteritis, K. Opengart Botulism, J. E. Dohms Gangrenous Dermatitis, K. Opengart 23 Other Bacterial Diseases 891 Introduction, H. J. Barnes Staphylococcosis, C. B. Andreasen Streptococcus and Enterococcus, S. G. Thayer, W. D. Waltman, and D. P. Wages Erysipelas, J. M. Bricker and Y. M. Saif Avian Intestinal Spirochetosis, D. J. Hampson and D. E. Swayne Tuberculosis, R. M. Fulton and S. Sanchez Other Bacterial Diseases, H. J. Barnes and L. K. Nolan 24 Avian Chlamydiosis (Psittacosis, Ornithosis) 971 A. A. Andersen and D. Vanrompay SECTION III: FUNGAL DISEASES 25 Fungal Infections, B. R. Charlton, R. P. Chin, and 989 H. J. Barnes Introduction Aspergillosis Candidiasis (Thrush) Dermatophytosis (Favus) Dactylariosis Sporadic Fungal Infections Histoplasmosis Cryptococcosis Zygomycosis (Phycomycosis) Macrorhabdosis (Megabacteria) SECTION IV: PARASITIC DISEASES 26 External Parasites and Poultry Pests 1011 N. C. Hinkle and L. Hickle 27 Internal Parasites 1025 Introduction, L. R. McDougald Nematodes, T. A. Yazwinski and C. A. Tucker Cestodes and Trematodes, L. R. McDougald 28 Protozoal Infections 1067 Introduction, L. R. McDougald Coccidiosis, L. R. McDougald and S. H. Fitz-Coy Cryptosporidiosis, L. R. McDougald Cochlosoma anatis Infection, A. J. Bermudez Histomoniasis (Blackhead) and Other Protozoan Diseases of the Intestinal Tract, L. R. McDougald Miscellaneous and Sporadic Protozoal Infections, A. J. Bermudez viii Contents
  8. 8. SECTION V: NONINFECTIOUS DISEASES 29 Nutritional Diseases 1121 K. C. Klasing 30 Developmental, Metabolic, and Other 1149 Noninfectious Disorders R. Crespo and H. L. Shivaprasad 31 Mycotoxicoses 1197 F. J. Hoerr 32 Other Toxins and Poisons 1231 R. M. Fulton SECTION VI: OTHER DISEASES 33 Emerging Diseases and Diseases of Complex or 1261 Unknown Etiology Introduction, Y. M. Saif Multicausal Respiratory Diseases, S. H. Kleven Multicausal Enteric Diseases, D. L. Reynolds Hypoglycemia-Spiking Mortality Syndrome of Broiler Chickens, J. F. Davis Proventriculitis and Proventricular Dilatation of Broiler Chickens, S. Hafner, M. A. Goodwin, J. S. Guy, and M. Pantin-Jackwood Index 1279 Contents ix
  9. 9. Brian M. Adair Veterinary Sciences Division Department of Agriculture & Rural Development Stoney Road Stormont, Belfast BT4 3SD Email: [email protected] Dennis J. Alexander Poultry Department Veterinary Laboratories Agency Weybridge New Haw, Weybridge Surrey KT15 3NB England Email: [email protected] A. Ali College of Veterinary Medicine Iowa State University Ames, IA 50011 Email: [email protected] Arthur A. Andersen National Animal Disease Center P.O. Box 70 Ames, IA 50010 Email: [email protected] Claire B. Andreasen Iowa State University Department of Veterinary Pathology College of Veterinary Medicine Ames, IA 50011-1250 Email: [email protected] H. John Barnes College of Veterinary Medicine North Carolina State University 4700 Hillsborough Raleigh, NC 27606 Email: [email protected] Alex J. Bermudez Veterinary Medical Diagnostic Laboratory University of Missouri-Columbia P.O. Box 6023 Columbia, MO 65205 Email: [email protected] Pat J. Blackall Animal Research Institute Locked Mail Bag No. 4 Moorooka Qld 4105 Australia Email: [email protected] Janet M. Bradbury The University of Liverpool Dept. of Veterinary Pathology Jordan Building Leahurst Neston Wirral, CH64 7TE England Email: [email protected] Joseph M. Bricker Pfizer Richland, MI 49083 Email: [email protected] B. W. Calnek Unit of Avian Medicine Department of Microbiology and Immunology College of Veterinary Medicine Cornell University Ithaca, NY 14853 Email: [email protected] David Cavanagh Institute for Animal Health Compton Laboratory Compton, Newbury Berkshire RG 20 7NN England Email [email protected] xi Contributing Authors
  10. 10. B.R. Charlton California Animal Health and Food Safety Laboratory University of California, Davis 2789 South Orange Avenue Fresno, CA 93725 Email: [email protected] Hans H. Cheng USDA/ARS Avian Disease and Oncology Laboratory Michigan State University E. Lansing, MI 48823 Email: [email protected] R. P. Chin California Animal Health and Food Safety Laboratory University of California, Davis 2789 South Orange Avenue Fresno, CA 93725 Email: [email protected] J.P. Christensen Department of Veterinary Microbiology The Royal Veterinary and Agricultural University Stigbojlen 4, DK 1870 Frederiksberg C, Denmark Email: [email protected] Rocio Crespo California Animal Health & Food Safety Laboratory System Fresno Branch 2789 S. Orange Avenue Fresno, CA 93725 Email: [email protected] James F. Davis Georgia Poultry Laboratory 4457 Oakwood Road P.O. Box 20 Oakwood, GA 30566 Email: [email protected] John E. Dohms Department of Animal and Food Sciences College of Agricultural Sciences University of Delaware Newark, DE 19717-1303 Email: [email protected] J. P. Duchatel Faculty of Veterinary Medicine University of Liege Liege, Belgium Email: [email protected] N. Eterradossi Unit de Virologie Immunologie et Parasitologie Aviaires et Cunicoles Agence Franaise de Scurit Sanitaire des Aliments (AFSSA) BP 53, 22440 Ploufragan, France Email: [email protected] Aly M. Fadly Avian Disease and Oncology Laboratory USDA Agricultural Research Service 3606 East Mount Hope Road East Lansing, MI 48823 Email: [email protected] N. Ferguson-Noel University of Georgia Athens, GA 30602 Email: [email protected] Steve Fitz-Coy Schering-Plough Corporation Salisbury, MD 21801 Email: [email protected] S.D. Fitzgerald Animal Health Diagnostic Laboratory College of Veterinary Medicine Michigan State University East Lansing, MI 48824 Email: [email protected] Richard M. Fulton G304 Veterinary Medical Center Animal Health Diagnostic Lab Michigan State University East Lansing, MI 48824-2152 Email: [email protected] Maricarmen Garcia Department of Population Health College of Veterinary Medicine University of Georgia 953 College Station Road Athens, GA 30602-4875 Email: [email protected] Richard K. Gast Egg Safety and Quality Research Unit SEPRL/USDA/ARS 950 College Station Road Athens, GA 30605 Email: [email protected] xii Contributing Authors
  11. 11. Jack Gelb, JR. Department of Animal and Food Sciences and Avian Biosciences Center University of Delaware Newark, DE 19716 Email: [email protected] G.Yan Ghazikhanian Nicholas Turkey Breeding Farms P.O. Box Y Sonoma, CA 95476 Email: [email protected] J. R. Glisson Department of Population Health College of Veterinary Medicine University of Georgia 953 College Station Road Athens, GA 30602-4875 Email: [email protected] Mark A. Goodwin 160 Lawrenceville Avenue Jefferson, GA 30549 Email: [email protected] Richard E. Gough Department of Avian Virology Veterinary Laboratories Agency Weybridge, New Haw Addlestone, Surrey KT15 3NB United Kingdom Email: [email protected] Jean-Luc Guerin Unit Productions Animales UMR Microbiologie Moleculaire Ecole Nationale Veterinarie de Toulouse 23, chemin des Capelles 31076 Toulouse Cedex 3 France Email: [email protected] James S. Guy Department of Population Health and Pathobiology College of Veterinary Medicine North Carolina State University 4700 Hillsborough Raleigh, NC 27606 Email: [email protected] H. M. Hafez Institute of Poultry Diseases Free University Berlin Koserstr 21 Berlin, 14195 Germany Email: [email protected] Scott Hafner 252 Ashbrook Drive Athens, GA 30605 Email: [email protected] David A. Halvorson 301 Veterinary Science 1971 Commonwealth Avenue University of Minnesota St. Paul, MN 55108 Email: [email protected] D.J. Hampson School of Veterinary and Biomedical Sciences Murdoch University Perth, Western Australia Email: [email protected] Chris S. Hayhow Biomune Company Lenexa, KS 66215 Email: [email protected] Leslie Hickle Synthetic Genomics Inc. LaJolla, CA 92037 Email: [email protected] Nancy C. Hinkle Department of Entomology University of Georgia Athens, GA 30602 Email: [email protected] Frederic J. Hoerr Thompson Bishop Sparks State Diagnostic Laboratory P.O. Box 2209 Auburn, AL 36831-2209 Email: [email protected] C. L. Hofacre Department of Avian Medicine College of Veterinary Medicine University of Georgia Athens, GA 30602-4875 Email: [email protected] Contributing Authors xiii
  12. 12. Tadao Imada National Institute of Animal Health Kannondai, Tsukuba 305 Japan Email: [email protected] Sherman W. Jack Mississippi State University College of Veterinary Medicine Box 9825 Mississippi State, MS 39762 Email: [email protected] Mark W. Jackwood Dept. of Avian Medicine College of Veterinary Medicine University of Georgia 953 College Station Road Athens, GA 30602-4875 Email: [email protected] R. C. Jones Department of Veterinary Pathology University of Liverpool Jordan Building Leahurst, Neston South Wirral L64 7TE United Kingdom Email: [email protected] Isabelle Kempf Unit Mycoplasmologie Bacteriologie Agence Francaise de Securite Sanitaire des Aliments (AFSSA) F-22440 Ploufragan France Email: [email protected] Kirk C. Klasing Department of Animal Sciences University of California-Davis Davis, CA 95616 Email: [email protected] Stanley H. Kleven Department of Avian Medicine College of Veterinary Medicine University of Georgia Athens, GA 30602-4875 Email: [email protected] Susan J. Lamont Department of Animal Science Iowa State University Ames, IA 50011 Email: [email protected] K. S. Latimer Department of Veterinary Pathology College of Veterinary Medicine University of Georgia Athens, GA 30602 Email: [email protected] David H. Ley Department of Food Animal & Equine Medicine College of Veterinary Medicine North Carolina State University 4700 Hillsborough Raleigh, NC 27606 Email: [email protected] Mertyn Malkinson Veterinary Services and Animal Health Kimron Veterinary Institute Beit Dagan, Israel 50250 Email: [email protected] Larry R. McDougald Department of Poultry Science University of Georgia Athens, GA 30602-4875 Email: [email protected] M. S. McNulty Department of Agriculture for Northern Ireland Veterinary Sciences Division Stormont, Belfast Northern Ireland BT4 3SD Email: [email protected] X. J. Meng Department of Biomedical Sciences and Pathobiology Virginia Polytechnic Institute and State University Blacksburg, VA 24061 Email: [email protected] Samia A. Metwally Foreign Animal Disease Diagnostic Laboratory Plum Island Animal Disease Center P.O. Box 848 Greenport, NJ 11944 Email: [email protected] Venugopal Nair Head, Viral Oncogenesis Group Institute for Animal Health Compton, Berkshire United Kingdom RG20 7NN Email: [email protected] xiv Contributing Authors
  13. 13. Lisa K. Nolan Department of Veterinary Microbiology and Preventive Medicine Iowa State University Ames, IA 50011 Email: [email protected] Kenneth Opengart Keystone Foods 6767 Old Madison Pike Bldg. 5, Suite 500 Huntsville, AL 35806 Email: [email protected] Mary Pantin-Jackwood USDA/ARS, Southeastern Poultry Research Lab 934 College Station Road Athens, GA 30605 Email: [email protected] Christine L. Payne Animal Health Laboratories Agriculture Western Australia Baron-Hay Court South Perth, WA 6151 Australia Email: [email protected] F. William Pierson Department of Large Animal Clinical Sciences VA-MD Regional College Vet. Med. Blacksburg, VA 24601 Email: [email protected] Rodney L. Reece NSW Department of Primary Industries Elizabeth Macarthur Agricultural Institute Private Mail Bag 8 Camden, NSW 2570 Australia Email: [email protected] Willie M. Reed School of Veterinary Medicine Purdue University Lynn Hall, room 1176 625 Harrison Street West Lafayette, IN 47907 Email: [email protected] Donald L. Reynolds Veterinary Medical Research Institute 2520 College of Veterinary Medicine Iowa State University, Ames, IA 50011 Email: [email protected] Y. M. Saif Food Animal Health Research Program, OARDC The Ohio State University 1680 Madison Avenue Wooster, OH 44691 Email: [email protected] Susan Sanchez Veterinary Medicine Diagnostic Laboratory University of Georgia Athens, GA 30602 Email: [email protected] T. S. Sandhu Cornell University Duck Research Laboratory Unit of Avian Medicine College of Veterinary Medicine 192 Old Country Road P.O. Box 217 Eastport, NY 11941 Email: [email protected] Karel A. Schat Unit of Avian Medicine Department of Microbiology and Immunology College of Veterinary Medicine Cornell University Ithaca, NY l4853 Email: [email protected] Stacey L. Schultz-Cherry Department of Medical Microbiology University of Wisconsin Madison, WI 53706 Email: [email protected] Dennis A. Senne USDA National Veterinary Laboratory Services Ames, IA 50010 Email: [email protected] Jagdev M. Sharma Department of Veterinary Pathobiology College of Veterinary Medicine University of Minnesota 1971 Commonwealth Avenue St. Paul, MN 55108 Email: [email protected] H. L. Shivaprasad California Animal Health and Food Safety Laboratory System Fresno Branch 2789 South Orange Avenue Fresno, CA 93725 Email: [email protected] Contributing Authors xv
  14. 14. Joan A. Smyth Department of Pathobiology University of Connecticut Storrs, CT 06269 Email: [email protected] Edgardo Soriano Centro de Investigacion Estudios Avanzados en Salud Animal (CIESA) Facultad de Medicina Veterinaria y Zootecnia (FMVZ) Universidad Autonoma del Estado de Mexico (UAEM) Instituto Literario No. 100 Toluca 50000, Mexico Email: [email protected] Bruce Stewart-Brown Perdue Farms P.O. Box 1537 Salisbury, MD 21802 Email: [email protected] David E. Swayne USDA/ARS Southeastern Poultry Research Lab 934 College Station Road Athens, GA 30605 Email: [email protected] Stephan G. Thayer Department of Population Health College of Veterinary Medicine University of Georgia 953 College Station Road Athens, GA 30602-4875 Email: [email protected] Deoki N. Tripathy Department of Veterinary Pathobiology College of Veterinary Medicine University of Illinois at Urbana-Champaign Urbana, IL 61801 Email: [email protected] Christopher A. Tucker Department of Animal Science University of Arkansas Fayetteville, AR 72704 Email: [email protected] Jean-Pierre Vaillancourt Department of Clinical Sciences University of Montreal St. Hyacinthe Quebec Email: [email protected] Paul C. M. Van Empel Bacteriological Research Department Intervet International B.V. Post-Box 31 5830 AA Boxmeer The Netherlands Email: [email protected] Vicky L. Van Santen Department of Pathobiology Auburn University Auburn, AL 36849 Email: [email protected] Daisy Vanrompay Laboratory of Gene Technology University of Leuven K. Mercierlaan 92 3001 Heverlee Belgium Email: [email protected] H. Vindevogel Faculty of Veterinary Medicine University of Liege Bld de Colonster 20/BAT B.42 4000 Liege Belgium Email: [email protected] Dennis P. Wages College of Veterinary Medicine North Carolina State University 4700 Hillsborough Raleigh, NC 27606 Email: [email protected] W. Douglas Waltman Georgia Poultry Diagnostic Laboratory Georgia Department of Agriculture Atlanta, GA 30334 Email: [email protected] R. L. Witter Avian Disease and Oncology Laboratory USDA Agricultural Research Service 3606 East Mount Hope Road East Lansing, MI 48823 Email: [email protected] Leslie W. Woods Department of Veterinary Sciences and Pathobiology University of Wyoming Laramie, WY 82070 Email: [email protected] xvi Contributing Authors
  15. 15. P. R. Woolcock California Veterinary Diagnostic Laboratory System Fresno Branch School of Veterinary Medicine University of California, Davis 2789 South Orange Avenue Fresno, CA 93725 Email: [email protected] Thomas A.Yazwinski Department of Animal Science University of Arkansas Fayetteville, AR 72701 Email: [email protected] Guillermo Zavala Department of Population Health College of Veterinary Medicine University of Georgia 953 College Station Road Athens, GA 30602-4875 Email: [email protected] Qijing Zhang Department of Veterinary Microbiology Iowa State University Ames, IA 50011 Email: [email protected] Contributing Authors xvii
  16. 16. The editorial board asked a distinguished colleague and former editor-in-chief of this book, Dr. Bruce Calnek, to write the Fore- word to this edition containing a historical account of Diseases of Poultry. We are indebted to Dr. Calnek for providing a compre- hensive account of the history of this book, which indeed should be preserved. Thank you, Bruce. This edition is fittingly dedicated to Dr. John Barnes, who served on the editorial boards of the eighth, ninth, tenth, and eleventh editions of Diseases of Poultry. Dr. Barnes contribu- tions have been instrumental in maintaining the high quality of this book, and, indeed, we are highly grateful for his efforts. Dr. Lisa Nolan joined the editorial board, and we are very apprecia- tive of her services. This edition represents a continuation of the tradition estab- lished earlier of providing the latest information on poultry dis- eases. Earlier trends of expansion of authorship to include au- thors from around the globe continued in this edition. Efforts continued to standardize the format of the chapters to enhance the search for specific items in a given chapter. All the book chapters were updated. There is one less chapter in this edition; some chapters were combined; and a new chapter was created. These changes were dictated by the increasing or de- creasing significance of some diseases or the increasing knowl- edge on a given disease. Some subchapters have been moved to different chapters because of recent findings indicating that they fit within different areas. The last chapter, Emerging Diseases and Diseases of Com- plex or Unknown Etiology, has always been in a state of flux be- cause of the nature of the topics included. Two subchapters of this chapter in the eleventh edition, labeled Big Liver and Spleen Diseases and Hepatitis Splenomegaly, were recently associ- ated with avian hepatitis E virus infection and moved to Chapter 14. In addition, the subchapter on viral proventriculitis was moved to this chapter because of the uncertainties of the etiology of the disease. The subchapter, Poult Enteritis and Mortality Syndrome, was combined with the subchapter, Multicausal Enteric Diseases, in recognition of the fact that it is a condition resulting from multiple infections. Chapter 1 was split in two, and a new chapter, Host Factors for Disease Resistance, was created. This was done in recogni- tion of the importance of the subject matter for a book on dis- eases and because of the increasing knowledge on the subject. The chapter on avian encephalomyelitis was combined with Chapter 14 in which coverage of similar infections is placed. The chapter on bordetellosis was combined with the chapter on pasteurellosis and other respiratory bacterial infections. A collective thank you goes to the authors who contributed to earlier editions of the book and those that contributed to the cur- rent edition. It has been a delightful experience working with all of you. The personnel at Wiley-Blackwell that worked on this edition have been most helpful and accommodating, and we sincerely appreciate their support. This is the second time that I served as editor-in-chief of Diseases of Poultry, and I (YMS) am indebted to my colleagues, the associate editors, for their tireless efforts in the review process and their support and advice. Finally, I would like to acknowledge a special person, my as- sociate Ms. Hannah Gehman. Her organizational skills, patience, speed, attention to details, and pleasant demeanor have been most helpful and appreciated. Editor-in-Chief Y.M. Saif Associate Editors A.M. Fadly J.R. Glisson L.R. McDougald L.K. Nolan D.E. Swayne xix Introduction
  17. 17. Previous forewords for Diseases of Poultry, beginning with the first one written by John R. Mohler in 1943, have briefly de- scribed the nature and contents of the edition, along with sub- stantive reasons for its publication and distribution to potential users. He pointed out that for a profitable poultry industry . . . knowledge of the characteristics of each disease is necessary . . . as the first step in building up an effective barrier against it. He further noted that . . . this unusually comprehensive book is intended for students, veterinarians, pathologists, and workers in specialized fields. These words are as applicable today as they were 65 years ago. For the sixth edition in 1972, Dr. P. P. Levine offered an ac- counting of some of the changes in the poultry industry that moved it from a small-scale farm activity to . . . a highly sophis- ticated industry marketing products worth over $6 billion per year in the United States alone. He correctly attributed some of the many advances in disease control through eradication, ge- netic selection, immunization practices, management improve- ments, and so on to major advances founded in research. Such new knowledge strongly dictates a need for revised texts. Levine further predicted that . . . infectious diseases will decline in im- portance; toxicologic, nutritional, genetic, and husbandry prob- lems will demand increasing attention. Change is the order of life, and avian diseases are no exception. In the seventh edition (1978), he pointed out many of the important new advances in identifying the etiology of several conditions, and the need for Diseases of Poultry to . . . keep up with the rapid developments in avian diseases. Ben Pomeroy, in the eighth (1984) and ninth (1991) editions, reiterated the need for new editions to keep up with the . . . ex- plosion of knowledge on the prevention and control of avian dis- eases. The inclusion of contributions from experts from many countries of the world and the importance of such in the face of global issues of disease control were emphasized by Charles Beard in the tenth (1997) edition. He pointed out that understand- ing the molecular genetics of causative agents is also important and that the use of molecular methods is necessary for poultry disease researchers to understand and control infectious diseases; yet another reason for timely updates. The message is clear: a changing and global poultry industry and its many allied industries need the most recent information available to keep pace with the challenges of providing adequate health care and disease prevention. It is important not only to poultry flocks, but also to the consumers who expect safe, as well as nutritious, poultry products. This, the twelfth edition, upholds the long-standing reputation of this book for keeping scientists, breeders, poultry producers, and poultry health professionals supplied with the latest and most comprehensive information available. Sixty-five years have passed since the first edition was printed. Before all details are lost forever, it is fitting to look back at how this bible in the field of poultry diseases came to be and how it has evolved into what it is today. It all began in the 1930s. In a memorandum addressed to the American Association of Avian Pathologists (AAAP), dated December 22, 1965, H. E. Biester related the events that preceded the decision by the Iowa State College (now University) Press (ISU Press) to undertake the pub- lication of Diseases of Poultry. During the 1930s, Louis DeVries, a member of the Department of Modern Languages at the college, translated a 1929 German book entitled Handbuch der Geflgelkrankheiten und der Geflgelzucht, published by Ferdinand Enke, Stuttgart. The translation lay dormant for sev- eral years until Dr. Campbell, the Chicago publisher of Veterinary Medicine, saw the translation and expressed some in- terest in it. Dr. Biester, who described himself as an innocent by- stander, having no special interest in the project told Dr. Campbell that the manuscript was unacceptable for a variety of reasons, and he suggested that if he were serious about publica- tion, then selected specialists should edit or rewrite the material. Dr. Biester later was pulled into the project, and he ultimately concluded that the German book was obsolete. Apparently, a number of contributors had accepted invitations to cooperate in developing an American book, and, according to Biester, they agreed that . . . it would be better to prepare a totally new book based on American conditions. Thus, the die was cast. Dr. Campbell gave up his plans, and ISU Press decided to publish an original text. Drs. Biester and DeVries served as editors, and 34 American investigators were engaged in the project. There were chapters on general subjects such as anatomy, digestion, genetics, hematology, hygiene and sanitation, nutrition, and surgery as well as those dealing with specific infectious and noninfectious diseases and conditions. A separate chapter dealt with diseases of turkeys. In 1943 the first edition was ready. The publication costs were considerable for a book that was thought to have limited distribution, so it was de- cided to omit royalties and accept a subsidy for illustrations from the dean of the college. Fifteen hundred copies were printed and placed on sale for $7.50. To everyones surprise, a second print- ing of 2,500 copies was needed after less than nine months, and there was yet another printing of 2,500 copies two years later. xxi Foreword
  18. 18. Royalties were then instituted! ISU Press was concerned that without some remuneration, the authors might be reluctant to re- main dedicated. The inclusion of Dr. DeVries as an editor is a bit puzzling since he had no medical background. Perhaps it was in recogni- tion of his effort with the translation of the German text. In any case, he was replaced in subsequent editions by Dr. L. H. Schwarte, a member of the Veterinary Research Institute in Ames who had written four chapters in the first edition. The book was thereafter referred to by many as Biester and Schwarte even for a period after they were no longer associated with it. They con- tinued at the helm through the fifth edition published in 1965. Although Dr. Schwarte contributed several chapters in each of the first five editions, Dr. Biester apparently confined his efforts to editorial tasks. Their memo to the AAAP stated that they both were responsible for making the index, and they personally checked practically all of the references because they felt that they owed to the reader accuracy. A total of 61 people served as authors under their editorial supervision; 12 of them con- tributed to all five editions. Ultimately, the passage of time dictated that Drs. Biester and Schwarte should relinquish their roles as editors, and they de- cided that the fifth edition (1965) would be their last. As noted in the preface to the sixth edition, it was their wish . . . that future editions of the book become the responsibility of the AAAP. . . ., which had become a strong and representative organization to which many of the users of Diseases of Poultry belonged. Also the AAAP was already in the business of publishing the journal Avian Diseases, so it was considered a logical move. The AAAP appointed a committee, chaired by Dr. M. S. Hofstad who had been one of the books authors and who was on the faculty in Ames. Drs. Biester, J. E. Williams, B. S. Pomeroy, and C. F. Helmboldt filled out the committee, and, in June 1966, they rec- ommended that the AAAP sponsor future editions of Diseases of Poultry, which would continue to be published by ISU Press in Ames. They asked the board of directors to appoint an editorial committee consisting of an editorial chairman and four associate editors by January 1, 1967. A letter from Dr. G. H. Snoeyenbos (AAAP secretary-treasurer) to Dr. C. A. Bottorff (AAAP presi- dent) dated November 23, 1966, suggested that Dr. P. P. Levine had declined a proposal that he assume the editorship of the book. Dr. Hofstad was subsequently named editor, and he per- sonally requested that Drs. Helmboldt, B. W. Calnek, W. M. Reid, and H. W. Yoder, Jr., be invited to be the associate editors. Each was given responsibility for a group of chapters that largely rep- resented their individual interests and strengths. An agreement between the AAAP and the ISU Press was executed on May 8, 1967, and it was agreed that manuscripts would be delivered to the publisher by September 1, 1969. So the transfer was complete and official. The sixth edition, under totally new editorial support, under- went some significant changes. The length of the book was be- ginning to be of concern and there was some discussion about perhaps needing to split it into two volumes. To avoid this, sev- eral chapters (anatomy, nutrition, genetics, and hematology) were eliminated based on good coverage in other publications. Also, there was a consolidation of other material; for instance all neo- plastic diseases were placed in a single chapter, and turkey dis- eases were incorporated in other chapters based on etiology. There were sweeping changes in authorship. Only 14 of the 40 contributors to the sixth edition had participated in the fifth edi- tion. Clearly, a new era had arrived! Also, following concern for the books length, Dr. Hofstad asked that the number of listed references be reduced by selective citation. He agreed that the reader should find, or be directed to, all pertinent literature on each of the covered topics, the latter through citation of review papers, etc. Space allocated to refer- ences became an issue in subsequent editions as well. In the sev- enth and eighth editions, titles of all references were removed. This was controversial and not all editors agreedincluding the author of this reviewand reference titles appeared again begin- ning with his tenure as editor of the ninth edition. Interestingly, based on the number of pages, the third edition (1,245 pages) was actually longer than the eleventh (1,231 pages). But by increas- ing page size, decreasing type size, and splitting into two columns per page, it was possible to include more than twice the amount of written material in the latter. Unlike the situation with Drs. Biester and Schwarte, citations and their accuracy became the responsibility of the individual au- thors. When it was observed that many errors existed, authors of the ninth edition were asked by Dr. Calnek to check every single reference against the original work so as to assure accuracy. This met with an enormous number of groans and considerable resist- ance until each author (with perhaps an exception or two) fol- lowed this strict instruction. The subsequent turn-around in their attitude was truly amazing when nearly all of them found errors, including the citation of references that did not even exist. It was not uncommon to detect mistakes in as many as 10 percent of ci- tations in some chapters, probably due in large part to a common practice of copying reference citations from other lists. Beginning with the ninth edition, the book entered the elec- tronic age. All material was submitted or copied into a word pro- cessing program that allowed spell-checking and reformatting. Initially, it was a tedious job, particularly because personal com- puters at that time were slow, and the skill of the individual au- thors in mastering a new approach varied considerably. However, improvements in software and computers and the possibility of rapid transfer of texts between authors, editors, and the publisher made the preparation of a new edition pleasurable compared to the old hard copy approach. There has been a continuum of changes that have improved Diseases of Poultry and kept it relevant over the years. For the tenth edition, the editors carefully reviewed and upgraded illus- trations, and, for the first time, included a number of color plates. Another major improvement that was gradually incorporated was the inclusion of molecular biology in many of the chapters. This was particularly important with regard to new applications of molecular techniques in diagnostic procedures, descriptions of etiological agents and significant elements of their molecular makeup, understanding the significance of selected genes in the pathogenesis of the diseases, and the development of genetically engineered vaccines. Our understanding of the fundamental na- xxii Foreword
  19. 19. ture of many diseases is now founded on the use of molecular ap- proaches in the research laboratory. Another of the more significant evolutionary changes was the addition of foreign authors to make the book truly international in flavor. One of the original AAAP-appointed editors argued strongly that Diseases of Poultry should be an American book, and the authorship was so aligned. The sixth edition had the first foreign contributor, although he (Bela Tumova, from Prague, Czechoslovakia) was actually a visiting professor at the University of Wisconsin working with B. C. Easterday on avian influenza at the time. It wasnt until the eighth edition that invi- tations to contribute to the book were extended to workers out- side of the United States. Drs. P. M. Biggs and L. N. Payne from England and Drs. J. B. McFerran and M. S. McNulty from Northern Ireland thus paved the way by providing parts of the chapters on neoplastic diseases, adenoviruses, and miscellaneous viral infections. The next edition (ninth) was truly international with 17 contributors from 9 countries outside of the U.S., and by the eleventh edition, there was a total of 34 different contributors from 13 countries. The world-wide reputation of the book was cer- tainly enhanced by the selection of authors based on their knowl- edge and contributions to our understanding of individual diseases and conditions without regard to their geographic location. The importance of Diseases of Poultry as a text for the world also is reflected in its translation into foreign languages or publi- cation in a copied form in other countries. There have been several authorized translations into Spanish, Chinese, and Russian, and an agreement between the publisher and India has allowed what is essentially a photocopied version of the original to be made. An ongoing review of the relative importance of individual diseases or conditions has led to a good deal of reshuffling over the years. Chapters have been added, combined, split, or elimi- nated to meet the changing picture of what is important to the field of avian diseases and disorders. Periodically, and especially with a change in authorship, major rewriting of some sections takes place. New chapters such as one dealing with new and emerging diseases appear when needed. Changes in editors occurred over the years so that by the eleventh edition, none of the 1968 group appointed by the AAAP remained. After riding herd on three editions (sixtheighth), Dr. Hofstad retired and was replaced by Dr. Calnek (ninth and tenth), and he, in turn, passed the baton to Dr. Y. M. Saif beginning with the eleventh edition. Likewise, associate editors who have re- placed or been added to the original group appointed by the AAAP in 1968 include Drs. H. J. Barnes (eightheleventh), C. W. Beard (ninth and tenth), L. R. McDougald (tenth), Y. M. Saif (tenth), J. R. Glisson (eleventh), A. M. Fadly (eleventh), D. E. Swayne (eleventh), and Lisa K. Nolan (twelfth). In summary, it is obvious that the bible in the field of avian diseases is an evolving, vibrant, and ever-current source of infor- mation relevant to all practitioners in the field of poultry medi- cine. It continues to be a reference source of significance to a vast number of people with many different relationships to the poultry industry. Bruce W. Calnek 12th Edition Diseases of Poultry Foreword xxiii
  20. 20. 12th Edition Diseases of Poultry
  21. 21. Introduction Alex J. Bermudez 3 Chapter 1 Principles of Disease Prevention: Diagnosis and Control This chapter acquaints the reader with the general concepts of poultry disease prevention, diagnosis, and treatment. It specifi- cally introduces the reader to management practices used in dis- ease prevention and poultry vaccination, principles of antimicro- bial therapy, and basic necropsy procedures. This chapter also provides information on insecticides and disinfectants. For infor- mation on specific diagnostic techniques and control measures, the reader is referred to the respective chapters covering specific diseases in this text. This chapter does not cover all the detailed disease control methods or all types of poultry but attempts only to outline and illustrate some fundamental concepts. Each poultry enterprise is different; therefore, these basic concepts must be applied accord- ing to conditions and facilities existing in individual situations. To keep abreast of the flow of research and information, a con- stant review of current literature and recommendations applica- ble to specific diseases, special enterprises, and various geo- graphic areas is necessary. Excellent journal sources of current information are Avian Diseases, Avian Pathology, Poultry Science, Journal of Applied Poultry Research, and Worlds Poultry Science Journal, and many publication and trade journals provide special emphasis on particular segments of poultry husbandry (e.g., Poultry International, International Hatchery Practice, Industria Avicola, Egg Industry, Watt Poultry USA, International Poultry Tribune, Poultry Times, and others, including publications in a variety of languages). Standard textbooks on chicken and turkey production, husbandry, and nutrition are other sources of information. A good practical manual on commercial chicken production is North and Bell (2). During the last three decades, the poultry industry has experi- enced many changes that have had a significant effect on the pre- vention and control of poultry diseases. One of the most signifi- cant changes has been the continued integration of poultry production companies and the consolidation of these companies and the allied industries that serve them. These changes have a profound effect on the poultry industry as the decision-making process becomes more centralized in poultry companies and fewer products and services become available with the mergers of biologic and pharmaceutical companies. While the poultry industry has changed significantly as the re- sult of internal market forces, it also experiences significant ex- ternal forces that are largely beyond its control. Examples of such forces include the globalization of the world economy, food safety issues, environmental concerns, animal welfare issues, and concerns about the use of antimicrobials in food animals. These external forces have a very direct impact on the activities of poul- try health professionals as they certify poultry or products for ex- port, address consumer concerns, and work to ensure the produc- tion of safe and wholesome poultry products. Although many of these topics are beyond the direct scope of this text, they can have a significant indirect or direct impact on the disease agents that affect poultry. Host-Parasite-Environment Relationship Disease results when normal body functions are impaired, and the degree of impairment determines the severity of the disease. It may result from the consequences of harmful actions of infec- tious and parasitic agents, or it may be caused by injury or phys- ical stress with which the bird cannot cope. Disease may also occur as the result of a deficiency of a vital nutrient or the inges- tion of a toxic substance. Diseases caused by infectious and parasitic agents are fre- quently complex and depend upon characteristics of the host, agent, and environmental conditions on the farm. Nutritional de- ficiencies may be temporary and reversible when the nutrient is supplied in adequate amounts; others are irreversible. Disease re- sulting from stress is related to its severity and duration. Injuries, such as extreme beak trimming, tend to persist for a long time and may be permanent. Whether disease results from parasitism depends on the num- ber, type, and virulence of the parasite; the route of entry to the body; and the defense status and capabilities of the host. The lat- ter depends partly on the hosts prior disease encounters (e.g., in- fectious bursal disease or IBD), nutritional status, and genetic ability to organize resistance mechanisms; environmental stresses; and the kind and timing of countermeasures employed (drugs or changes of environment). Some virulent organisms, such as highly pathogenic avian in- fluenza, rapidly overcome the resistance of even the healthiest hosts. Less virulent strains or types cause moderate to severe ill-
  22. 22. ness, but most birds respond and return to a state of health. Still other strains or types cause no marked reaction, and the host shows little or no obvious signs of ill health. Some infectious agents may not cause dramatic effects themselves but predispose the host to more serious infections by other agents. Some mi- croorganisms are not considered pathogenic because they usually are found in and around individuals considered normal; it must be recognized, however, that so-called nonpathogenic and low pathogenic organisms can also cause serious losses when the right environmental circumstances exist. Severe physical stresses such as chilling, overheating, water deprivation, starvation, and concurrent infection by other disease agents can reduce the hosts ability to resist and, thus, may precipitate a disease condition that can be detected (e.g., clinical mycoplasmosis following infec- tious bronchitis or clinical salmonellosis in chilled or water- deprived chicks). Coccidiosis provides a good example of the relationship be- tween the number of invading organisms and the severity of the resulting infection, because the morbidity and mortality of the host species are usually proportional to the number of sporulated coccidial oocysts ingested. Environmental conditions still play a significant role, however, as litter conditions will affect both the rate of oocyst sporulation and survival. A similar situation exists for many other infectious diseases. A mild roundworm infection may not be serious; whereas a severe infection can be very detri- mental. A good reason for removing moribund and dead birds from a flock is to reduce the number of infectious organisms available to penmates. Thorough washing and disinfecting of a building may not render it sterile, but it can reduce the number of infectious organisms to such a low level that they cannot cause disease. By following sound disease-preventive practices before and after the arrival of new flocks; making sure that the flock has ad- equate, properly placed, good quality feed and water; applying judicious and timely vaccines and medications; and providing a less stressful environment, the poultry producer can control the probability of a flock becoming infected, as well as the severity and outcome of an infection. Influence of Modern Practices Avian disease specialists continually must seek new knowledge about the nature and control of specific diseases. Meanwhile, persons responsible for the production of poultry meat, table- and hatching-eggs, chicks and poults, feed ingredients, and mixed feeds should practice the basic techniques and management prin- ciples that will prevent occurrence of disease. They should also provide the physical facilities and quarantine capabilities neces- sary for control and elimination of diseases that occasionally gain entrance so that they do not become a continuing problem. Economic losses, sometimes relatively subtle, resulting from dis- ease can mean the difference between success and failure in the poultry business. Those who disregard the basic principles of dis- ease prevention may succeed in times of a favorable market but do not remain competitive when the margin of profit is very small. A new modern enterprise with many good buildings and labor-saving equipment, but constructed and operated without re- gard to fundamental disease control and eradication principles, may function free of disease for a few years. All too frequently, a troublesome disease gains entrance and thereafter becomes a constant costly burden because of the extreme cost of depopula- tion required to eradicate it. When new farms and buildings are designed and constructed and production is programmed with the objective of excluding diseases or eradicating them when they gain entry, poultry can be maintained free of most harmful diseases in a practical manner with reasonable effort. The poultry producer who uses funda- mental management practices that prevent disease outbreaks has little need for detailed knowledge of the many infectious diseases affecting poultry. Facilities need not be new to be adequate. Frequently, old farms can be enlarged and production reprogrammed to exclude or eradicate disease. Many old poultry buildings, hatcheries, and feed mills can be redesigned to favor exclusion, eradication, or control of disease. Strict application of disease-preventive man- agement techniques has enabled producers to maintain specific- pathogen-free chickens on farms of standard design and con- struction (1). The trend in all agricultural industries continues toward larger units, fewer farmers, and corporate enterprise. The chicken and turkey industries have been leaders in this trend, which has placed emphasis on efficiency and lower costs of production. Survival in the industry has depended upon continual adoption of newer and more efficient practices. It is sometimes forgotten that efficiency in disease prevention is as important as efficiency in cleaning, feeding, bird handling, and egg processing. The result- ing evolution of management systems has altered the emphasis in disease-control practices and will continue to do so (e.g., the shift in placing layer flocks in multi-flock complexes rather than single-age farms has eliminated the possibility of all-in, all-out production and provides a much greater challenge to the flock manager in the control of respiratory disease). Corporation farming accelerated the move toward integrated control and operation of two or more segments of the industry, such as feed manufacturing, breeder flock management, hatchery operation, pullet rearing, broiler and turkey grow-out phases, lay- ing farm production, egg processing, turkey and broiler slaughter and processing, retail distribution, and further processing of poultry products. Integration of the industry has concentrated under one decision-making body the disease control practices for millions of birds, as well as several phases in the production chain of eggs and meat. Thus, sound health practices and emer- gency quarantine measures decided upon by one or a few individ- uals can be applied quickly and effectively to large numbers of birds. Through integration, it has become economically practical to employ veterinarians full time and to place responsibility for disease control directly in the hands of specialized poultry veteri- narians. Disease considerations are sometimes reduced to simple cost accounting, whereby the economic loss from a disease and the costs of treating it are weighed against the costs of its eradi- cation and of maintenance of the clean status, before determining the course of action. Poultry production managers must be care- ful not to make decisions that produce short-term cost savings 4 Diseases of Poultry
  23. 23. but potentially greater negative long-term cost effects as the re- sult of a higher disease incidence. Examples of such potential shortsighted cost savings are the excessive dilution of Mareks disease vaccine, reusing litter in turkey brooding facilities, and excessively shortening the turn-around time between production flocks. The poultry industry can no longer be considered to be com- posed of localized businesses limited to certain states or areas. It is characterized by multistate and often multinational companies that move products daily between widespread locations and mar- kets. Because of the high cost of scientific poultry breeding, pro- ducers throughout the world depend on a few organizations for their highly efficient breeding and production stocks. In the case of turkeys, most of the worlds breeding stock originates from one of three locations in North America. For such a system to function smoothly and efficiently, widespread and daily ship- ments of hatching eggs, poults, chicks, started pullets, and adult fowl across state and national boundaries are essential and neces- sitate reevaluation of old concepts of health regulations. Specialized poultry veterinarians and state and federal livestock health officials have evolved to guide the course of health control measures. Diagnostic facilities, both private and government, are available in major poultry-producing areas of the world. Except where importation and use are restricted by government regula- tion, high-quality vaccines and drugs are available wherever poultry is raised commercially. Good quality feed is the rule, not the exception, in the modern poultry industry. Despite significant advances, disease still takes a heavy toll from all types of poultry enterprise. Those who exercise farm management decisions (caretaker, owner, flock supervisor, cor- porate manager, money lender) have the power to reduce these losses through management for disease control. They must be made aware of the responsibilities and continually encouraged to develop a philosophy of disease prevention through management and to concentrate on amortized long-term advantages and not just short-term savings. With better control over diseases of all kinds, providing opti- mum bird comfort throughout the house has become a very im- portant management factor in obtaining maximum performance. That is not achieved solely by windowless, insulated, light- and temperature-controlled houses. Such factors as overcrowding, poor beak trimming, uneven temperatures, and uncomfortable air currents on caged birds that cannot move to a more comfortable location also adversely affect performance. Proper orientation of feeders, waterers, and light promotes good performance; slight, seemingly insignificant changes from proven systems can have a pronounced adverse effect on performance of both caged and floor-housed flocks of chickens and other commercial fowl. Poor performance of adults is often traceable to detrimental events that occurred during the rearing period. An attentive and skilled farm manager is of great importance in the successful production of poultry flocks. References 1. Chute, H. L., D. R. Stauffer, and D. C. OMeara. 1964. The produc- tion of specific-pathogen-free (SPF) broilers in Maine. Maine Agric Exp Stn Bull 633. 2. North, M. O. and D. D. Bell. 1990. Commercial Chicken Production Manual, 4th ed. Chapman & Hall: New York, NY. CHAPTER 1 Principles of Disease Prevention: Diagnosis and Control 5 Disease Prevention and Diagnosis Alex J. Bermudez and Bruce Stewart-Brown Breeder Flock Management The breeder flock must be managed in such a way so as to opti- mize the production of clean fertile hatching eggs in an eco- nomic fashion. This management program must ensure that the chicks or poults produced will be viable from both an immuno- logic and nutritional perspective when they are placed in the pro- duction setting. The science of effective breeder flock manage- ment is somewhat beyond the scope of this text, and a reference on this topic has been published by Leeson and Summers (34). Disease prevention measures must also be in place to prevent diseases that will result in morbidity and mortality in the breeder flock itself. Finally, the breeder flock should be managed so that egg-borne diseases are prevented by whatever techniques are available. Diet, Health, and Parental Immunity A breeder ration must contain a higher level of many nutrients than does a laying ration. Laying rations sufficient to sustain egg production are not adequate to sustain good hatchability and health of young offspring. In some cases, production is satisfac- tory in breeder hens, but their embryos or chicks show symptoms and lesions of vitamin deficiency. The breeder ration must be ad- equate for development of the embryo and the chick as well as egg production performance of the breeder hen. The minimum nutri- tional requirements of breeder flocks are well characterized in the Nutritional Requirements of Poultry (44) published by the National Research Council. Poultry nutritionists responsible for the nutrition of commercial breeder flocks frequently supplement the nutrient inputs of breeder flocks beyond these minimum re- quirements to provide an additional margin of safety in the ration. Meat birds are bred to grow fast and large, but the flocks kept for breeding must have feed intake restricted to prevent obesity and poor adult performance. Feed restriction must be carefully controlled to prevent aggressive birds from getting most of the available feed. Two systems are widely used: daily restriction and skip-a-day feeding. The former requires special feeding equip-
  24. 24. ment or procedures to ensure that feed is presented to the entire flock simultaneously so that all birds begin eating at the same time. In the skip-a-day system, feed is given in larger quantities on alternate days, permitting the recessive birds to obtain their share even if they have to wait their turn to eat. In either system, special provision must be made in formulating feeds to provide adequate coccidiostat and essential nutrients in the reduced amount consumed. Breeder hens in poor health for any reason frequently fail to supply the embryo with some vital nutritional factor(s) or per- haps pass some toxic material to the egg; thus, the hatch is poor or chicks are of low quality and must be culled. A good example of such a problem is breeder hens infected with capillaria worms; they may produce progeny that are deficient in vitamin A. While this occasionally happens with apparently healthy birds also, a clinically healthy breeder flock is the best insurance of good quality offspring. Young poultry are delivered into many types of environments. In some areas, husbandry methods are such that birds are ex- posed to disease from the first day of life. In some cases, expo- sure of very young poultry lacking any maternal antibodies to a disease can lead to significant mortality or economic loss (infec- tious bronchitis, avian encephalomyelitis, IBD, or duck virus hepatitis). Where exposure is apt to occur at a very early age, ma- ternal antibody can be a significant aid to prevention of disease. However, a high level of maternal antibodies can interfere with early immunization. How much maternal immunity is desirable and against how many diseases are debatable subjects and will vary according to the area where poultry are raised and the type of rearing facility (cage versus floor). Maternal immunity is dissipated gradually and usually does not last more than 24 weeks after hatch. In modern, well-run layer and breeder replacement-rearing facilities chicks and poults are well protected, not only against the elements, but also against introduction of disease from outside sources for several weeks or beyond the time that a high initial maternal immunity would be protective. Maternal immunity in chicks is of less concern in such cases. This is not so likely to be true of inadequately sani- tized and poorly managed pullet-rearing or broiler grow-out farms, where exposure can occur as early as the first day of life to a disease agent carried over from the previous brood in reused built-up litter. In these cases, protective maternal antibodies be- come a very important consideration in preventing disease or re- ducing losses, and vaccinating breeder dams with killed vaccines to give high maternal antibody protection for the offspring has become common practice. Lesions and residues from the carrier for killed vaccines injected into the breast muscle have been cause for carcass condemnation at slaughter. Interior Egg-Borne Diseases Various techniques are used for preventing disease agents from being transmitted from dam to offspring via the egg. The ideal situation is to have breeders free of all pathogens. For most viral diseases, there is still no practical way of obtaining this utopian situation. For others (avian encephalomyelitis), the probability of the infection occurring during the egg-laying period, with result- ant egg transmission, is too great to permit the clean but suscep- tible status (see Chapter 14). Immunization In addition to immunization of breeders against several common diseases to prevent adverse effects of inopportune infections on egg production, they are immunized against avian en- cephalomyelitis during the growing period to ensure that they do not become naturally infected during the period they are produc- ing hatching eggs. Although this may not be an absolute guaran- tee against egg transmission of the virus, it has been a practical means of preventing its serious dissemination through infected offspring. Testing and Removal of Carriers Carriers of some transovarially transmitted diseases can be de- tected by serologic or other means, and this procedure has been used to eliminate possible egg shedders from breeding flocks. Historically, this has proved to be an important starting point in the successful eradication of pullorum disease and fowl ty- phoid. Similar programs currently are practiced by primary breeder companies to reduce the vertical transmission of lym- phoid leucosis. Testing and Slaughter of Infected Flocks Where infected breeders are detected, the entire flock may be de- stroyed. This method is indicated in circumstances whereby test- ing is not likely to detect all infected birds. It is a costly proce- dure and not warranted unless there is a definite advantage for the offspring and reasonable assurance that they will not become infected from other sources after delivery to the farm. It has been used successfully for eliminating mycoplasma-infected turkey and chicken breeder flocks. Destruction of Agent inside the Egg A pressure differential between the atmosphere and the inside of the egg has been used to force antibiotics through the shell of in- cubating eggs to prevent transmission of pathogenic Mycoplasma species from dam to offspring. This is done by dipping warm eggs into cold antibiotic solutions or using special vacuum ma- chines (2). Antibiotics have also been injected directly into eggs for this purpose (40). Elevating the egg temperature has also been used to destroy mycoplasmas inside the egg (76). In this procedure, incubator temperature (and internal egg temperature) gradually is raised over a 1214-hour period to the maximum embryo survival tem- perature, approximately 46.9C and then cooled immediately and rapidly to normal incubation temperatures. The procedure usu- ally lowers hatchability. Treatment of Offspring Offspring from infected dams may be treated with high levels of antibiotics by injection or feeding or both. This is unreliable, but can be a significant adjunct to other methods and can greatly as- sist in overcoming economic losses from egg-transmitted dis- eases that are drug sensitive. 6 Diseases of Poultry
  25. 25. Eggshell-Borne Diseases Several procedures are used to overcome shell contamination that arises from intestinal contents and other environmental sources. Control involves preventing shell contamination or destroying or- ganisms before they penetrate the shell. Egg penetration by bacteria occurs more readily if the shell be- comes porous. This occurs in the late life of the breeder hen or when there is a deficiency or imbalance between calcium, phos- phorus, and vitamin D. Respiratory virus infections can also re- sult in porous and poor shells. Management of Hatching Eggs Clean Hatching Eggs Very dirty eggs should not be used for hatching. If they must be used, they should be dry-cleaned when gathered. The cleaner the shell surface, the less likelihood there will be bacterial contami- nation and shell penetration. The most important consideration in hatching egg sanitation is to manage the flock so that eggs are clean when gathered. Many factors enter into accomplishing this goal. Sloping wire-bottom rollaway nests, with or without automatic collecting devices, generally result in clean eggs and a minimum of bacterial con- tamination. Clean eggs can also be produced in conventional box-type nests if nesting material is diligently kept clean by continually re- placing soiled material. Egg breakage can be reduced by provid- ing sufficient nests for the peak laying period. The number of floor and yard eggs can be reduced by proper design and location of nests when maturing pullets need them; location and design will vary with the type of house. Nests should be darkened and ventilated, and hens must be prevented from roosting in them at night, because they contaminate the area with fecal deposits. Keeping the litter dry is an aid in preventing soiled nests and nest material. Proper design and construction of the breeder house to create conditions conducive to keeping litter dry aids disease control at the hatching-egg level. Table-egg breeding stock perform satisfactorily in litterless housingeither all slat or sloping wire-floor housesand this largely eliminates dirty eggs resulting from tracking litter and feces into the nests. Heavy breeds and turkeys do not perform as well on these floors, so combinations of part slat and part litter are used to aid in litter management. Measures should be taken to prevent Salmonella infections by using Salmonella-free feed ingredients, particularly meat meal, eliminating these pathogens from mixed feed (pelleting), keeping feed clean by good feeding practices and storage facilities, and keeping natural carriers (rodents, wild birds, pets) out of pens and houses. Preventing salmonellosis and other types of enteric infections also helps prevent wet droppings, which contribute to wet litter. Above all, eggs should be gathered frequently, especially in the early part of the day when most hens visit the nests. They should be gathered in clean, dry equipment and held in a dry, dust-free area. Sanitization of Eggs The shell surface of hatching eggs should be disinfected imme- diately after gathering. If sanitization or fumigation cannot be done on the farm, it should be done as soon as possible thereafter, preferably before eggs enter the hatchery building or at the en- trance to the egg-processing area. The more delayed the sanitiza- tion, the less effective it is because the bacteria will have had longer to penetrate the shell. Unsanitized eggs raise the possibil- ity of carrying a serious infection into the hatchery where suscep- tible newly hatched chicks are present (see Disinfectants, For- maldehyde). Because of possible adverse health considerations resulting from the inhalation of formaldehyde fumes, farm and hatchery personnel should be alert for any new and effective shell sterilization compounds and methods that may become available. Washing and Liquid Sterilization Washing eggs with warm detergent solution at a temperature (43 51.8C) always higher than that of the eggs entering the washing machineat least 16.6C higher but not to exceed 54C followed by sanitizing the shells with a chlorine compound, quater- nary ammonia product, or other sanitizing agent is routine for commercial eggs. The procedure has been employed successfully with hatching eggs, but some real disasters have occurred where thousands of eggs were contaminated rather than sanitized when dirty water was used, especially in recirculating washing machines. Even if eggs are washed properly, very dirty eggs should be cleaned first by sanding to prevent excessive pollution of the wash- ing solution and equipment. If the iron content of the wash water exceeds 5 ppm, it favors multiplication of certain types of bacteria and creates a serious egg spoilage problem. A complete review of egg sanitizing agents is presented by Scott and Swetnam (57). If egg washing is done, it should be only with a type of ma- chine (brush conveyor type using flow-through wash water prin- ciple) that will ensure against contamination with dirty wash or rinse water. Very careful supervision is also necessary to see that all equipment is working properly at all times and is cleaned daily. In some types of machines, if the washing system fails, a few eggs can contaminate the water and, thus, contaminate thou- sands of others before the problem is detected and corrected. Contaminated eggs in the incubator set off a chain reaction of egg explosions that contaminate surrounding eggs, causing more ex- ploders and more contamination. While washing and liquid ster- ilization of hatching eggs can be done satisfactorily, the proce- dure is subject to operational difficulties and should not be attempted without full knowledge of the hazards involved. Whenever cold eggs are moved into a warm, humid atmos- phere, moisture condenses on the cold shells (called sweating). This moisture provides a medium for the growth of bacteria and fungi already present on dirty or unsanitized shells or originates in contaminated warm air around the eggs. Cold eggs should, therefore, be warmed to room temperature in clean, low humid- ity air before placing them in an incubator. Storage Facilities After fumigation or other shell sterilization, hatching eggs are frequently stored in a cool room (about 10C) at the hatchery CHAPTER 1 Principles of Disease Prevention: Diagnosis and Control 7
  26. 26. until set. Cool rooms should be clean and free of mold and bac- teria and periodically disinfected to prevent recontamination of shells. Holding hatching eggs too long or under improper storage temperature, humidity, and environment can result in poor qual- ity chicks. Clinical histories indicate that infection in young chicks may sometimes be traceable to fungus-contaminated hatching eggs; infections have been produced experimentally by contaminating shells with fungus spores (75). Hatchery Management The building and equipment in which the fertile egg is converted to a day-old chick, poult, or other fowl and the equipment used to process and deliver it to the farm must be clean and sanitary. An individual hatched from a pathogen-free egg will remain pathogen-free only if it hatches in a clean hatcher, is put in a clean box and held in a clean room where it can breathe clean air, and then is hauled to the farm in a clean delivery van. Design and Location A hatchery should be located away from sources of poultry pathogens such as poultry farms, processing plants, necropsy laboratories, rendering plants, and feed mills. It is not good prac- tice to retail poultry equipment and supplies from a hatchery building, because this draws producers and service workers who may introduce contaminating material. A good hatchery design has a one-way traffic flow from the egg-entry room through egg-traying, incubation, hatching, and holding rooms to chick-loading area. The cleanup area and hatch-waste discharge should be off the hatching room, with a separate load-out area. Each hatchery room should be designed for thorough washing and disinfecting. The ventilation system is equally important and must be designed to prevent recirculation of contaminated and dust-laden air. Gentry et al. (26) found that hatcheries with poor floor designs and faulty traffic patterns were highly contaminated compared with those with one-way flow. Importance of Good Sanitation Factors that aid in obtaining pathogen-free chicks and poults are hatchery cleanliness and sanitation, well-arranged traffic flow, and well-controlled ventilation. Techniques have been devised for evaluating the sanitary sta- tus of commercial hatcheries by culturing fluff samples (74), de- tecting microbial populations in hatchery air samples (19, 26, 36), and culturing various surfaces in the hatchery (38). By relat- ing results of these techniques to hatchery management, it has been observed by Magwood (37) that bacterial counts of egg- shells dropped quickly in clean air, and low counts persisted on all surfaces to completion of hatching. Chute and Barden (18) found fungal flora of hatcheries to be related to management and sanitation programs. To minimize bacterial contamination of eggs and hatching chicks, hatchery premises must be kept free of reservoirs of con- tamination, which readily become airborne (37). Trays used for hatching should be thoroughly cleaned with water and then dis- infected before eggs are placed in them. This can be done by dip- ping in a tank of suitable disinfectant (see Disinfectants), washing with hot water or steam followed with disinfectant spray, or fumigating with formaldehyde in the hatcher. Trays and eggs are frequently fumigated together immediately after eggs are transferred to the hatcher. Fumigation is sometimes done during the hatch (at about 10% hatch), but concentrations low enough to avoid harming the hatching chick probably serve only to give the down a pleasing yellow color. Formaldehyde fumigation in one case increased the severity of mold infection rather than over- coming it (75). Wright (72) emphasized the practical meaning of hatchery sanitation and how to attain it. He concluded that no fu- migation program should be used to replace cleanliness, but rather to supplement it. As chicks hatch, the exposed embryo fluids collect bacteria from contaminated shells, trays, and ventilating air. The combi- nation of the nutritious fluids and warm temperature forms an ex- cellent environment for bacteria and they multiply very rapidly (26). The cleaner the air and environment to begin with, the more the bacterial buildup is delayed and, as the hatch progresses, the less likely is the navel to become infected (omphalitis). Breeder Codes The breeder code is a designation used to denote the source of hatching eggs. It usually denotes breeders of the same age on the same or different farms, all breeders on a particular farm, or any other grouping. There is a tendency to keep breeders in larger flocks and to avoid as much as practicable the mixing of hatch- ing eggs from flocks of many different microbial, nutritional, and genetic backgrounds. If breeders are kept free of disease and fed a good ration, hatching eggs are produced clean and properly dis- infected, and chicks are hatched and handled in clean surround- ings. Keeping chicks of different breeder codes separated has lit- tle practical meaning other than providing that all have more nearly the same level of maternal antibodies against the same dis- eases. This may permit a more uniform response to vaccines ap- plied to chicks the first 23 weeks of life when maternal antibod- ies have a protective effect. Occasionally, a disease is believed to be egg transmitted from a breeder flock to the offspring. When this occurs, the disease nearly always appears in several offspring flocks derived from the same breeder flock(s) and delivered to different farms. However, a hatch of chicks is frequently divided into deliveries to several farms and a disease occurs in only those delivered to one farm. This indicates that the disease is farm associated and not hatchery or breeder-flock associated. Chick Sexers Unless the output of one hatchery is so great as to demand their full time, chick sexers may go from one hatchery to another, which introduces the possibility of carrying disease. Most sexers are aware of this hazard and are eager to follow proper biosecu- rity procedures. If sexers must also service other hatcheries, fa- cilities should be provided so that their equipment can remain at the hatchery. They should have a clean area in which to change clothes and wash themselves and their equipment and should 8 Diseases of Poultry
  27. 27. have clean protective garments to wear. Their habits should be at least as clean as those of the hatchery crew. Surgical Procedures Poultry can be very cannibalistic under certain circumstances, and beak trimming is commonly practiced in breeder flocks as well as production turkeys and cage layers. In these production systems, beak trimming is a virtual necessity, and special ma- chines have been manufactured for this purpose. Beak trimming is performed on birds of various ages, depending on the hus- bandry system in use. The extremely dim light used in light-tight poultry houses greatly reduces or prevents cannibalism, but chicks reared under natural or bright light may have their beaks trimmed lightly at 1 day of age or a few days after delivery to the brooder. This early mild trimming is not severe enough to be per- manent; therefore, beaks of such flocks of breeders or commer- cial layers are frequently trimmed again before maturity. Some methods and ages of early beak trimming can protect chickens from cannibalism throughout life if other management factors (e.g., light intensity) are favorable. When this is done properly, there is no serious adverse effect; however, proper beak trimming is more an art than a science, and many birds are permanently handicapped when it is not done properly. If the operation is done correctly, after the beak tip is removed, the remaining growing tip is cauterized sufficiently with the hot cutter blade to prevent bleeding and regrowth, but not so much that the bird develops a sensitive or abnormal beak that interferes with eating and drinking. Proper beak trimming promotes maxi- mum performance. Done improperly, it is probably the greatest single management cause of unsatisfactory performance of lay- ing and breeding stock. Poor performance resulting from im- proper beak trimming must not be attributed to some mysterious disease. For more detail on cannibalism and beak trimming, see Chapter 30. Similarly, other surgical procedures, such as remov- ing wattles, combs, or toenails of certain toes, must be done by one trained in the procedure if harm to the bird is to be avoided. Management Factors in Disease Prevention The more important physical principles of disease prevention in- clude favorable geographic location of the farm in respect to other poultry units, proper location of buildings in relation to each other and to prevailing wind currents, proper design of the building inside and out, and design and positioning of equip- ment. Long-range planning and programming of the operation, whether large or small, is very important and should consider movement patterns of various vehicles and equipment, work traf- fic of regular and holiday caretakers and special work crews, feed delivery and storage, and the system for moving eggs and flocks from the farm. An avian pathologist can be helpful in avoiding some common pitfalls, but to avoid high-risk disease situations, consultation should be done when the farm is being designed and the production programmed, rather than after it is developed and serious trouble is evident. Good disease-prevention practices are perhaps best illustrated as a chain that is only as strong as its weakest link. Many sound principles can be discredited by failure to carry out one or two re- lated ones, which are either overlooked or not considered essen- tial. Although it may not always be possible to use all the prac- tices, the more that are followed, the greater the chances of avoiding disease outbreaks. Adult Flocks Modern laying strains are bred for high egg production, and broiler stocks are bred for rapid growth and good feed conver- sion. The most important management factor is maintaining feed, water, and environmental conditions at the optimum condition for hen comfort, which in turn results in maximum efficient pro- duction and growth. The same is required of meat birds, turkeys, and other types of breeder hens. The egg production or efficiency of feed use will be a good indicator of the success of the manage- ment and the welfare of the flock. Many conditions arise that hamper performance, and it is important not only to keep disease out, but to prevent conditions causing discomfort. Isolation Not all producers follow the same disease control practices. A close neighbor may disregard sound principles and be burdened with diseases until forced out of business by economic pressures. In the meantime, disease agents present on his premises may be blown or carried by various vectors and fomites to adjacent premises; thus, a disease occasionally may gain entrance even on well-managed units. Until a disease has been eradicated, it serves as a reservoir and potential source of infection for future flocks on the same premises and those on adjacent premises. The closer the houses of one premises to those of another, the more likely is the spread of infection to healthy birds on an adjacent farm. Some highly concentrated poultry areas have developed be- cause of some favorable condition such as a close market, an available slaughter or processing plant, an accessible feed supply, low-cost land, or favorable climate or zoning. Usually, these areas deteriorate into problem zones of disease of one type or another and resemble huge megafarms with many managers, each vac- cinating, treating, or exposing birds without regard to the pro- grams of others. Because such areas are in competition for mar- kets, several things may happen. Various advantages may offset disease losses, or the additional cost of production resulting from disease may price the product (meat, eggs) out of the market. In extreme cases, products cannot be marketed either because of the disease or the residues from drugs used to control disease. Producers who do not minimize losses go out of business, and many abandoned poultry farms are purchased or leased by other poultry producers. Some move their operations to a less concen- trated area where they usually escape disease, unless they take their problems with them knowingly or inadvertently through careless- ness. Those who remain usually upgrade disease-prevention prac- tices by redesigning houses and reprogramming the production cycle. Frequently, reprogramming proceeds to a system of a single age of fowl, permitting complete depopulation at the end of each rearing or laying cycle. Another solution to area disease problems where farms are too CHAPTER 1 Principles of Disease Prevention: Diagnosis and Control 9
  28. 28. close even for systematic depopulation to succeed is to develop a coordinated area depopulation and restocking program. All flocks in a reasonably defined geographic area may be marketed at the same time and the houses refilled at the same time. This is more adaptable to broiler production than egg production. Most serious disease problems could be avoided if a philoso- phy of premise isolation prevailed from the beginning of an en- terprise. No exact minimum distance from other poultry farms can be stated because this is influenced by prevailing winds, cli- mate, type of houses, and other factors. The farther from other poultry farms, the less likelihood of contracting disease from them. Isolation can be effected by taking advantage of segre- gating space provided by natural or artificial barriers such as bodies of water, hills, cities or towns, or forests, or other inter- posing agriculture enterprises such as grain, vegetable, or fruit production. One Age of Fowl per Farm Removing carriers from a flock and premises is an effective way of preventing a recurrence of some diseases, but it is impossible or impractical for others. The best way to prevent infection from carrier birds is to remove the entire flock from the farm before any new replacements are added and to rear young stock in com- plete isolation from older recovered birds on a separated farm segment or preferably on another farm and in an isolated area. This practice is often called all-in, all-out production. Where birds of different ages exist on a large farm, depopula- tion seems drastic, but considering mortality, poor performance, and endless drug expense, it could be the most economical solu- tion. Farms and quarantinable farm divisions of up to 100,000 birds of one age prove that size is no deterrent to application of the sound principle of one age of bird per farm or quarantinable segment with programmed depopulation at the end of the produc- tion cycle. Where only one age of bird is maintained, depopulation occurs each time pullets or poults are moved to the layer or breeder premises, each time the broilers or turkeys are moved to slaugh- ter, and each time the old layers or breeders are sent to market. Should a disease occur, the flock can be quarantined, treated, and handled in the best way possible until its disposal. Depopulated premises are then cleaned out, washed, and disinfected, and left idle for as long as possible but at least for 2 weeks before new healthy stock is introduced. Depopulation is most effective in controlling disease agents that do not survive for long outside the bird. This applies to most respiratory infections (mycoplasma infections, infectious coryza, and laryngotracheitis). It is least effective in controlling disease agents having a resistant state that survives for long periods in nature (intestinal parasites or clostridia). Started-pullet and pullet-rearing premises are now an estab- lished specialized enterprise in the poultry industry. This system has made layer and breeder farm depopulation more practical and successful. As on multiple-age layer farms, serious disease prob- lems may develop and persist on multiple-age rearing farms until they are reprogrammed for a single age or divided into quaran- tinable, isolated units. In addition to sanitary practices, environmental factors (tem- perature, humidity) play an important role in the time interval necessary to prevent carryover of disease. Disease germs begin to die out slowly after elimination from the body. Some (infectious coryza) die out very quickly; others (parasites and coccidia) sur- vive for months or years, depending on whether they develop a resistant stage and on factors discussed in the sections on those individual diseases. In general, the longer a premises remains va- cant, the lower the number of surviving pathogens. Functional Units For certain economic reasons (breeding farm or small specialized market trade), it is not always possible to limit the entire farm to a single age of poultry. In such instances, it should be divided into separate quarantinable units or areas for different groups of birds (rearing area, pedigree unit, production groups, and exper- imental birds) (Fig. 1.1). With a suitable arrangement, each area periodically is depopulated, cleaned, and sanitize