Pain Management in Veterinary Practice

(1)

(2)

www.ajpdf.com

(3)

Pain Management in Veterinary Practice

www.ajpdf.com

(4)

www.ajpdf.com

(5)

Pain Management in Veterinary Practice

Editors

Christine M. Egger Lydia Love Tom Doherty

www.ajpdf.com

(6)

This edition first published 2014^C 2014 by John Wiley & Sons, Inc.

Editorial offices: 1606 Golden Aspen Drive, Suites 103 and 104, Ames, Iowa 50010, USA The Atrium, Southern Gate, Chichester, West Sussex, PO19 8SQ, UK 9600 Garsington Road, Oxford, OX4 2DQ, UK

For details of our global editorial offices, for customer services and for information about how to apply for permission to reuse the copyright material in this book please see our website at www.wiley.com/wiley-blackwell.

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 codes for users of the Transactional Reporting Service are ISBN-13: 978-0-8138-1224-3/2014.

Designations used by companies to distinguish their products are often claimed as trademarks. All brand names and product names used in this book are trade names, service marks, trademarks or registered trademarks of their respective owners. The publisher is not associated with any product or vendor mentioned in this book.

The contents of this work are intended to further general scientific research, understanding, and discussion only and are not intended and should not be relied upon as recommending or promoting a specific method, diagnosis, or treatment by health science practitioners for any particular patient. The publisher and the author make no representations or warranties with respect to the accuracy or completeness of the contents of this work and specifically disclaim all warranties, including without limitation any implied warranties of fitness for a particular purpose. In view of ongoing research, equipment modifications, changes in governmental regulations, and the constant flow of information relating to the use of medicines, equipment, and devices, the reader is urged to review and evaluate the information provided in the package insert or instructions for each medicine, equipment, or device for, among other things, any changes in the instructions or indication of usage and for added warnings and precautions. Readers should consult with a specialist where appropriate. The fact that an organization or Website is referred to in this work as a citation and/or a potential source of further information does not mean that the author or the publisher endorses the information the organization or Website may provide or recommendations it may make. Further, readers should be aware that Internet Websites listed in this work may have changed or disappeared between when this work was written and when it is read. No warranty may be created or extended by any promotional statements for this work. Neither the publisher nor the author shall be liable for any damages arising herefrom.

Library of Congress Cataloging-in-Publication Data

Pain management in veterinary practice / editors, Christine M. Egger, Lydia Love, Tom Doherty.

pages ; cm

Includes bibliographical references and index.

ISBN 978-0-8138-1224-3 (pbk. : alk. paper) – ISBN 978-1-118-76133-5 (emobi) – ISBN 978-1-118-76134-2 (epdf) – ISBN 978-1-118-76160-1 (epub) 1. Pain in animals–Treatment. I. Egger, Christine M., editor of compilation.

II. Love, Lydia, editor of compilation. III. Doherty, T. J. (Tom J.), editor of compilation.

[DNLM: 1. Pain Management–veterinary. 2. Veterinary Medicine–methods. SF 925]

SF910.P34P35 2014 636.08960472–dc23

2013024797 A catalogue record for this book is available from the British Library.

Wiley also publishes its books in a variety of electronic formats. Some content that appears in print may not be available in electronic books.

Cover images: Front cover, Top and Bottom Left: Gregory Hirshoren, University of Tennessee CVM; Back Cover, Left: Kristie Mozzachio and Valarie V. Tynes; Middle and Right: Gregory Hirshoren

Cover design by Modern Alchemy LLC

Set in 9.5/11.5 pt Times by Aptara^R Inc., New Delhi, India

1 2014

www.ajpdf.com

(7)

Section 1: Introduction and Anatomy, Physiology, and Pathophysiology of Pain 1

1 Introduction: Pain: An Issue of Animal Welfare 3

Alice Crook

2 Anatomy, Physiology, and Pathophysiology of Pain 9

Yael Shilo and Peter J. Pascoe

3 Mechanisms of Cancer Pain 29

Cholawat Pacharinsak and Alvin J. Beitz

Section 2: Pharmacology of Analgesic Drugs 39

4 Opioids 41

Tanya Duke-Novakovski

5 Nonsteroidal Anti-Inflammatory Drugs and Corticosteroids 69

Stuart Clark-Price

6 Local Anesthetics 85

Kip A. Lemke

7 ␣-2 Adrenoceptor Agonists 93

Reza Seddighi

8 Nontraditional Analgesic Agents 105

Lydia Love and Dave Thompson

9 Novel Methods of Analgesic Drug Delivery 115

Lesley J. Smith

10 Pharmacokinetic Principles for the Design of Intravenous Infusions 125

Bruno H. Pypendop

Section 3: Nonpharmacological Pain Therapy 131

11 Canine Rehabilitation 133

Lowri Davies

12 Equine Rehabilitation 147

Lowri Davies

13 Custom External Coaptation as a Pain Management Tool: Veterinary Orthotics and Prosthetics 155 Martin W. Kaufmann and Patrice M. Mich

14 Myofascial Pain Syndrome in Dogs 161

Rick Wall

15 Traditional Chinese Herbal Medicine and Homeopathy in Pain Management 171 Lynelle Graham, Mona Boudreaux, and Steve Marsden

16 Mechanisms of Acupuncture Analgesia 177

Shauna Cantwell

v www.ajpdf.com

(8)

vi Contents

17 Equine Acupuncture 183

Arthur I. Ortenburger

18 Canine Chiropractic and Pain Management 189

Robin Downing

19 Equine Chiropractic 195

Henry S. Adair

Section: 4 Management of Pain in Veterinary Species 199

20 Recognition and Assessment of Acute Pain in the Dog 201

Kate L. White

21 Treatment of Acute Pain in the Dog 209

Kate L. White

22 Recognition and Assessment of Chronic Pain in Dogs 227

Anna Hielm-Bj ¨orkman

23 Treatment of Chronic Pain in Dogs 239

Anna Hielm-Bj ¨orkman

24 The Recognition and Assessment of Pain in Cats 269

Kersti Seksel

25 Treatment of Acute Pain in Cats 275

Jacob A. Johnson

26 Treatment and Assessment of Chronic Pain in Cats 289

Bonnie Wright and Jessica K. Rychel

27 Cancer-associated Pain and its Management 299

Lydia Love and Lisa DiBernardi

28 Recognition and Treatment of Pain in the Small Animal Critical Care Patient 311 Jane Quandt

29 Recognition and Assessment of Pain in Horses 317

Emma Love

30 Treatment of Acute and Chronic Pain in Horses 323

Bernd Driessen and Laura Zarucco

31 Recognition and Assessment of Pain in Ruminants 349

Kevin J. Stafford

32 Treatment of Acute and Chronic Pain in Ruminants 359

Alexander Valverde

33 Recognition and Treatment of Pain in Camelids 373

Tamara Grubb

34 Recognition and Treatment of Pain in Pet Pigs 383

Kristie Mozzachio and Valarie V. Tynes

35 Recognition and Assessment of Pain in Small Exotic Mammals 391

Lesa Thompson

36 Treatment of Pain in Small Exotic Mammals 399

Cheryl B. Greenacre

37 Recognition and Treatment of Pain in Birds 407

Karen L. Machin

38 Recognition and Treatment of Pain in Reptiles, Amphibians, and Fish 417 Lysa Pam Posner and Sathya K. Chinnadurai

www.ajpdf.com

(9)

Contents vii

Section 5: Incorporating Pain Management into Your Practice and Hospice and Palliative Care 425

39 Integrating Pain Management into Veterinary Practice 427

Robin Downing

40 Pain Management in Hospice and Palliative Care 431

Keri Jones

Index 437

www.ajpdf.com

(10)

www.ajpdf.com

(11)

Contributors

Henry S. Adair, DVM, MS, CERP, DACVS, DACVSMR Associate Professor, Equine Surgery

Director of Equine Performance and Rehabilitation Department of Large Animal Clinical Sciences College of Veterinary Medicine

University of Tennessee Knoxville, TN

Alvin J. Beitz, BS, PhD Professor and Chair Distinguished Teacher

Department of Veterinary and Biomedical Sciences College of Veterinary Medicine, University of Minnesota St. Paul, MN

Mona Boudreaux DVM, CVA, MMQ Owner

A Time To Heal Wonder Lake, IL

Shauna Cantwell, DVM, MVSc, CVA, CVSMT, DACVAA Courtesy Professor

University of Florida

Medicine Wheel Veterinary Services, Inc.

Ocala, FL

Sathya K. Chinnadurai, DVM, MS, DACZM, DACVAA Associate Veterinarian

Chicago Zoological Society/Brookfield Zoo Brookfield, IL

Stuart Clark-Price, DVM, MS, DACVIM-LA, DACVAA Assistant Professor, Anesthesia and Analgesia

Head, Anesthesia Clinical Service

Department of Veterinary Clinical Medicine College of Veterinary Medicine

University of Illinois Urbana, IL

Alice Crook, BSc, DVM Coordinator

Sir James Dunn Animal Welfare Centre Adjunct Professor

Department of Companion Animals Atlantic Veterinary College University of Prince Edward Island Charlottetown, Canada

Lowri Davies, BVSc, MRCVS, CVA, CCRP The SMART Veterinary Clinic Ltd

Weigbridge Referral Center Swansea, Wales, UK

Lisa DiBernardi, DVM, DACVIM (Oncology), DACVR (Radiation Oncology)

Animal Specialty Hospital of Florida Naples, FL

Palm Beach Veterinary Specialists West Palm Beach, FL

Robin Downing, DVM, CVPP, CCRP, DAAPM Hospital Director

The Downing Center for Animal Pain Management, LLC Windsor, CO

Bernd Driessen, DVM, PhD, DACVAA, DECVPT Professor, Anesthesiology

School of Veterinary Medicine University of Pennsylvania New Bolton Center Kennett Square, PA

Tanya Duke-Novakovski, BVetMed, MSc, DVA, DACVAA, DECVAA

Professor, Veterinary Anesthesiology and Analgesia Department of Small Animal Clinical Sciences Western College of Veterinary Medicine University of Saskatchewan

Saskatoon, Canada

Lynelle Graham, DVM, MS, DACVAA Clinical Professor of Anesthesia Veterinary Clinical Sciences University of Minnesota St. Paul, MN

Cheryl B. Greenacre, DVM, DABVP (Avian), DABVP (Exotic Companion Mammal)

Professor, Avian and Zoological Medicine Department of Small Animal Clinical Sciences College of Veterinary Medicine

ix

(12)

x Contributors

Tamara Grubb, DVM, PhD, DACVAA

Assistant Clinical Professor, Anesthesia and Analgesia Veterinary Clinical Sciences

Washington State University Pullman, WA

Anna Hielm-Bj¨orkman, DVM, PhD, CVA (IVAS) Assistant Professor

Department of Equine and Small Animal Medicine Pain and Rehabilitation Clinic and Research Center Faculty of Veterinary Medicine

Helsinki University Helsinki, Finland

Jacob A. Johnson, DVM, DACVAA

Assistant Professor, Anesthesia and Pain Management Auburn University College of Veterinary Medicine Auburn, AL

Keri Jones, DVM, CVPP Medical Director

Homeward Bound Animal Hospital Arvada, CO

Martin W. Kaufmann, ABC, c-PED OrthoPets

Center for Animal Pain Management and Mobility Solutions Denver, CO

Kip A. Lemke, BS, DVM, MS, DACVAA Professor, Anesthesiology

Chief of Anesthesiology Service Department of Companion Animals College of Veterinary Medicine University of Prince Edward Island Charlottetown, Canada

Emma Love, BVMS, PhD, DVA, DECVAA, MRCVS, FHEA, RCVS

Senior Teaching Fellow in Veterinary Anaesthesia University of Bristol

Bristol, UK

Lydia Love, DVM, DACVAA

Director of Anesthesia and Pain Management Animal Emergency and Referral Associates Fairfield, NJ

Karen L. Machin, DVM, PhD Associate Professor

Department of Veterinary Biomedical Sciences Western College of Veterinary Medicine University of Saskatchewan

Saskatoon, Canada

Steve Marsden, DVM, ND, MSOM, Lac, Dipl.CH, CVA Director

College of Integrative Veterinary Therapies Edmonton, Canada

Patrice M. Mich, DVM, MS, DABVP, DACVAA, CCRT Medical Director

OrthoPets

Center for Animal Pain Management and Mobility Solutions Denver, CO

Kristie Mozzachio, DVM, DACVP Mozzachio Mobile Veterinary Services Hillsborough, NC

Adjunct faculty

North Carolina State University College of Veterinary Medicine Raleigh, NC

Arthur I. Ortenburger, DVM, MS Associate Professor of Surgery Department of Health Management University of Prince Edward Island Charlottetown, Canada

Cholawat Pacharinsak, DVM, MS, PhD, DACVAA Assistant Professor

Director of Anesthesia, Pain Management, and Surgery School of Medicine

Stanford University Stanford, CA

Peter J. Pascoe, BVSc, DVA, DACVAA, DECVAA Professor, Veterinary Anesthesia and Critical Patient Care Department of Surgical and Radiological Sciences, School of Veterinary Medicine

University of California Davis, CA

Lysa Pam Posner, DVM, DACVAA Associate Professor Anesthesiology Director of Anesthesia Services College of Veterinary Medicine North Carolina State University Raleigh, NC

Bruno H. Pypendop, DrMedVet, DrVetSci, DACVAA Professor, Veterinary Anesthesia and Critical Patient Care Department of Surgical and Radiological Sciences School of Veterinary Medicine

University of California Davis, CA

Jane Quandt, DVM, MS, DACVAA, DACVECC Associate Professor, Anesthesiology

College of Veterinary Medicine University of Georgia

Athens, GA

Jessica K. Rychel, DVM, CVMA, CCRP Veterinary Emergency and Rehabilitation Hospital Fort Collins, CO

(13)

Contributors xi

Reza Seddighi, DVM, MS, PhD, DACVAA Assistant Professor, Anesthesia and Analgesia Department of Large Animal Clinical Sciences College of Veterinary Medicine

Kersti Seksel, BVSc (Hons), MRCVS, MA (Hons), FACVSc, DACVB, CMAVA, DECVBM-CA

Registered Veterinary Specialist, Behavioral Medicine Sydney Animal Behavior Service

Seaforth, Australia

Yael Shilo, DVM, DACVAA Senior Anesthesiologist, Anesthesia Department Veterinary Teaching Hospital Koret School of Veterinary Medicine The Hebrew University of Jerusalem Rehovot, Israel

Lesley J. Smith, DVM, DACVAA

Clinical Professor of Anesthesiology and Pain Management Department of Surgical Sciences

School of Veterinary Medicine University of Wisconsin Madison, WI

Kevin J. Stafford, MVB, MSc, PhD, FRCVS, FANZCVSc Professor

Institute of Veterinary Animal and Biomedical Sciences Massey University

Palmerston North, New Zealand Dave Thompson, DVM Clyde Park Veterinary Clinic Wyoming, MI

Lesa Thompson, MA, BVM&S, DZooMed (Mammalian), MSc, MRCVS, RCVS Tokyo, Japan

Valarie V. Tynes, DVM, DACVB Premier Veterinary Behavior Consulting Sweetwater, TX

Alexander Valverde, DVM, DVSc, DACVAA Associate Professor, Anesthesiology

Department of Clinical Studies Ontario Veterinary College University of Guelph Guelph, Canada

Rick Wall, DVM, CCRP, DAAPM Certified Myofascial Trigger Point Therapist

Center for Veterinary Pain Management and Rehabilitation The Woodlands, TX

Kate L. White, MA, Vet MB, DVA, DECVAA, MRCVS Clinical Associate Professor, Anesthesia

Head of Division of Medicine College of Veterinary Medicine University of Nottingham Sutton Bonington Campus Loughborough, UK

Bonnie Wright, DVM, DACVA, CVMA, CVPP, CCRP Veterinary Emergency and Rehabilitation Hospital Fort Collins, CO

Laura Zarucco, DMV, PhD Associate Professor of Surgery Dipartimento di Scienze Veterinarie Scuola di Agraria e Medicina Veterinaria Universit`a degli Studi di Torino

Grugliasco, Italy

(14)

(15)

Preface

New analgesics and new formulations of old analgesics are con- stantly being introduced to the veterinary market, yet the ability to recognize and quantify pain in veterinary species remains a challenge. Pain assessment and scoring systems are being validated in many veterinary species, but clinically relevant, objective methods of assessment of all types of pain in all species remain elusive.

Ultimately, it is left to the caregiver to decide if analgesic therapy is indicated, and this requires empathy and logic. The purpose of this book is to provide the reader with easily accessible, evidence- based information to aid in the recognition and treatment of pain in veterinary species.

ORGANIZATION AND FEATURES OF THE BOOK Section I begins with an introductory chapter discussing welfare issues associated with pain and its management in veterinary species. The chapters that follow provide a review of the current understanding of the physiology and pathophysiology of acute pain, chronic pain, and cancer pain.

Section II provides extensive information about the pharmacology of opioids, nonsteroidal anti-inflammatory drugs, alpha-2 adrenoreceptor agonists, local anesthetics, and non-traditional analgesics (e.g., anti-epileptic drugs, NMDA receptor antagonists, and nutritional supplements). Novel methods of drug delivery and the pharmacokinetics of continuous rate infusions are also discussed.

The non-pharmacological management of pain, including physical therapy, orthotics and prosthetics, myofascial trigger point therapy, acupuncture, chiropractic, herbal therapy, and homeopathy are discussed in Section III. These chapters are not intended to provide expert training in these areas. They are meant to provide a basic explanation of some techniques that can be easily incorporated into

daily practice and to discuss scientific evidence, or lack thereof, supporting these modalities.

The recognition and treatment of acute and chronic pain in dogs, cats, small exotic mammals, birds, reptiles, amphibians, fish, camelids, ruminants, pigs, and horses is discussed in Sec- tion IV. Chapters on the treatment of cancer pain and the recognition and treatment of pain in intensive care patients are also included. The chapters in this section discuss pharmacological and non-pharmacological strategies for use in each species to provide a balanced pain management protocol. Much of the information from these chapters is summarized in tables to allow easy access to information.

The fifth and final section includes a chapter describing strategies for incorporating pain management into veterinary practice, including some economic and legal considerations, and a final chapter discussing veterinary hospice and palliative care.

ACKNOWLEDGMENTS

The authors wish to thank the staff of Wiley for their support and encouragement. This work would not have been possible without the contributions of the authors who come from academic, research, and clinical practice backgrounds in the USA, Canada, Great Britain, Europe, New Zealand, and Australia. A feature common to all is the desire to improve the recognition, prevention, and treatment of pain in animals. We hope that this book contributes significantly to that endeavor.

Christine M. Egger Lydia Love Tom Doherty

xiii

(16)

(17)

Section 1 Introduction and Anatomy, Physiology, and Pathophysiology of Pain

Chapter 1. Introduction: Pain: An Issue of Animal Welfare 3

Alice Crook

Chapter 2. Anatomy, Physiology, and Pathophysiology of Pain 9

Yael Shilo and Peter J. Pascoe

Chapter 3. Mechanisms of Cancer Pain 29 Cholawat Pacharinsak and Alvin J. Beitz

Pain Management in Veterinary Practice, First Edition. Edited by Christine M. Egger, Lydia Love and Tom Doherty.

C2014 John Wiley & Sons, Inc. Published 2014 by John Wiley & Sons, Inc.

1

(18)

(19)

1 Introduction: Pain: An Issue of Animal Welfare

Alice Crook

There has been considerable progress since the early 1990s in pain research in animals and in our understanding of related physiology and pharmacology, enabling great strides to be made in pain management. But pain is still a huge welfare issue for animals:

farm animals are routinely subjected to painful husbandry procedures with no anesthesia or analgesia; perioperative pain management in small and exotic animals is inconsistent; and management of cancer-related and chronic pain remains a challenge. Pain can diminish animal well-being substantially due to its aversive nature, the distress arising from the inability to avoid such sensations, and the secondary effects that may adversely affect the animal’s quality of life (QOL). Pain may affect an animal’s appetite, sleep habits (e.g., fatigue), grooming (e.g., self-mutilation), ability to experience normal pleasures (e.g., reduced play and social interaction), personality and temperament, and intestinal function (e.g., consti- pation), and may prolong the time needed for recovery from the underlying condition (ACVA, 1998; McMillan, 2003). Untreated pain may also result in systemic problems; for example, hepatic lipidosis in cats as a result of inappetance and inadequate caloric intake (Mathews, 2000).

Much is known about the recognition and assessment of pain in animals; however, more work is needed to develop valid and reliable pain scoring systems for all species that are practical in real- life situations. Perception of animal pain directly affects analgesic usage, and there is a wide range in attitudes among veterinarians, farmers, and pet owners. This can best be addressed through education. There are also economic, regulatory, and other constraints to effective pain management, particularly in large animals.

RECOGNITION AND ASSESSMENT OF PAIN IN ANIMALS

Pain is an unpleasant sensory and emotional experience associated with actual or potential tissue damage, or described in terms of such damage (IASP, 1994). The experience of pain is always subjective.

Self-reporting is the gold standard in people, yet how can we know the experience of animals?

Three approaches are used in the recognition and measurement of pain in animals. The first approach includes measures of gen-

eral body function or productivity (e.g., food and water intake, weight gain) that are relatively easy to quantify; such measures reflect what was happening to the animal over the period between observations. The second approach includes physiological measures (such as changes in heart rate or cortisol concentrations) that are widely used in studies assessing pain in animals (Stafford &

Mellor, 2005; Vickers et al., 2005; Whay et al., 2005) and are, in principle, particularly useful in prey species that are consid- ered stoic and therefore unlikely to show pronounced behavioral responses until injuries are advanced (Phillips, 2002; Rutherford, 2002). However, the physical restraint required to obtain such measurements may itself be stressful and confound the results (Weary et al., 2006). Also, while cortisol measurements are useful for comparing treatments and controls, they are not useful in assessing the degree of pain an individual animal is experiencing (Rutherford, 2002).

Behavioral measures—the third approach—represent a way in which animals can “self-report.” Weary (2006) provides a compre- hensive review of the ways such measures are used to recognize and quantify animal pain, and discusses the evidence necessary to ensure that the measures are valid (i.e., that the measure provides useful information about the pain the animal is experiencing) and reliable (i.e., repeatable). The three main classes of behavior used in pain assessment are pain-specific behaviors (e.g., gait impair- ment in lame dairy cows (Flower et al., 2008) or head shaking and rubbing in dehorned dairy calves (Vickers et al., 2005)); a decline in frequency or magnitude of certain behaviors (e.g., loco- motory behaviors in rats postoperatively) (Roughan & Flecknell, 2003); and choice or preference testing (e.g., hens’ responses to different concentrations of carbon dioxide used in stunning) (Web- ster & Fletcher, 2004). Rutherford (2002) discusses the usefulness of behaviors associated with acute, subacute, and longer-lasting pain in assessing the experience of pain in animals, including specific parameters that may be useful for veterinarians in clinical assessment of pain and by scientists studying pain in animals.

These include simple and more complex behavioral responses, both qualitative and quantitative, which may or may not be adaptive, such as behaviors associated with escape or avoidance, guarding or protection (e.g., postural changes), and depression or “learned helplessness.”

3

(20)

4 Section 1 / Introduction and Anatomy, Physiology, and Pathophysiology of Pain Pain Recognition Tools

Pain researchers and clinicians alike agree that there is a need for sensitive and specific measures that are practical for real-time assessments in a variety of animal settings including farms, veterinary clinics, and laboratories (Vi˜nuela-Fern´andez et al., 2007).

Multidimensional pain scales that integrate objective and subjective behavioral observations with various other measures can be used to characterize an individual animal’s experience of pain (Ruther- ford, 2002). Another approach is to develop questionnaires for use by animal owners that can be used in the assessment of pain and its impact on QOL (McMillan, 2003; Wiseman-Orr et al., 2004;

Yazbek & Fantoni, 2005). Wiseman-Orr (2006) provides a thor- ough discussion of the approaches and potential pitfalls of designing and validating questionnaires where self-reporting is not possible and the questionnaires are designed for use by a proxy, as in the case of animals. Work continues in the development of scientif- ically validated pain recognition tools for veterinarians for clinical assessment of pain and for scientists studying pain in large, small, exotic, and laboratory animals (Roughan & Flecknell, 2003;

Wiseman-Orr et al., 2004; Yazbek & Fantoni, 2005; Morton, 2005;

Wojciechowska et al., 2005; F ¨ollmi et al., 2007; Flecknell et al, 2007; Weary & Fraser, 2008).

PAIN AND CONSCIOUSNESS

Pain is always subjective and psychological variables such as past experience, attention, and other cognitive activities affect the individual’s experience of pain (Melzack, 1993). Self-reporting is the gold standard in people and, because of the subtlety of communi- cation possible with language, the understanding of pain has been greatly advanced through human subjects’ descriptions of pain and the effects of different modalities of analgesia (Johnson, 2008).

However, “The inability to communicate verbally does not negate the possibility that an individual is experiencing pain and is in need of appropriate pain-relieving treatment” (IASP, 1994).

If we cannot know the subjective emotional experiences of other human beings, how can we possibly know the emotional experience of animals? For most people, the evidence that animals have nociceptive receptors and pathways, physiological responses, and behavioral reactions to pain similar to that of people, is sufficient to accept that animals experience pain and suffer as a result. However, some scientists, surprisingly, suggest that animals are not capable of experiencing pain. Psychologist Bermond (2001), for example argues that animals other than anthropoid apes have an “irreflex- ive consciousness” (a consciousness without past or future) due to the lack of a well-developed prefrontal cortex, and that reflection is a requirement to experience suffering and pain as unpleasant.

Therefore, he distinguishes between “the registration of pain as a stimulus, which does not induce feelings of suffering and the experience of pain as an emotion, which does induce suffering”

(Bermond, 2001).

What kind of observations can provide evidence for or against the experience of pain and other affective states in animals? The neuro- physiologist Gentle (2001) carried out an elegant series of studies to provide information on cognitive perception of pain in chickens by looking at the effect of selective attention on pain-related behavior. Noting that the human experience of pain can be modu- lated by shifts in attention through such modalities as relaxation

training, hypnosis, and other therapies, he reasoned that if a chicken’s response to a painful event was simply an unconscious automatic reaction the response would not be influenced by shift- ing the bird’s attention. On the other hand, if the bird actually felt the pain as an unpleasant experience, redirecting its attention might reduce the signs of pain, as in people (e.g., installation of overhead television screens in dental offices). In his work, Gentle induced gout in one leg of chickens by injecting sodium urate crys- tals. Chickens kept in barren cages avoided placing weight on the affected leg and, if encouraged to walk, did so with a limp. These pain-related behavioral signs were greatly reduced or eliminated in chickens given a variety of motivational changes including nesting, feeding, exploration, and social interaction. The shifts in attention not only reduced pain but also reduced peripheral inflammation.

This work has far-reaching consequences. The evidence that motivational changes, by altering the birds’ attention, significantly altered pain-related behaviors, and hence probably the pain experience for the animal, indicates a cognitive component of pain in the chicken and provides evidence of consciousness. On a practical level, these results also reinforce the importance of environmental enrichment, which will promote shifts in attention and, thereby, potentially improve the welfare of birds suffering pain under com- mercial conditions. Strategies, such as distraction and refocusing attention through positive interaction, are very familiar to veterinarians and animal health technicians as adjuncts to pain management in small animals in clinical settings.

ATTITUDES TOWARD ANIMAL PAIN

“Freedom from pain, injury, or disease (by prevention or rapid diagnosis and treatment)” is one of the Five Freedoms widely accepted as the major components of good animal welfare (Farm Animal Welfare Council, 2009). The recognition and effective treatment of pain is central to animal welfare (Rutherford, 2002). There is a strong emphasis on pain among animal welfare researchers, with the number of pain-related articles in scientific journals consider- ably outweighing articles on the other Freedoms (freedom to behave normally, freedom from fear and distress, freedom from hunger and thirst, and freedom from discomfort) (Phillips, 2008).

National animal welfare advisory bodies in Australia, New Zealand, and the European Union have recommended steps to avoid or minimize animal pain and associated suffering, and the World Organization for Animal Health (OIE) produced a special edition in its Technical Series on “Scientific assessment and management of animal pain” (Mellor et al., 2008). Veterinary associations commonly have positions or policies advocating the effective management of pain in animals (CVMA, 2007; AVMA, 2011).

In theory, then, we agree that animals should not be in pain, yet studies show that attitudes toward pain vary greatly among societal groups responsible for animal care, including veterinarians. Vet- erinary attitudes toward pain and pain management in companion and production animals have been studied in Canada (Dohoo &

Dohoo, 1996; Hewson et al., 2006b, 2007a, 2007b), the United States (Hellyer et al., 1999), the United Kingdom (Lascelles et al., 1999; Capner et al., 1999; Huxley, 2006), Finland (Raekallio et al., 2003), Scandinavia (Thomsen et al., 2010), Europe (Hugonnard et al., 2004; Guatteo et al., 2008), and New Zealand (Laven et al., 2009). Other surveys have looked at the attitudes of veterinary and

(21)

1 / Introduction: Pain: An Issue of Animal Welfare 5 animal science students (Levine et al., 2005; Heleski & Zanella,

2006; Kielland et al., 2009).

These studies reveal some common themes. Considerable variation in clinical recognition and treatment of pain exists in both companion and production animal practice. A perception that an animal is in pain is a decisive factor in the provision of analgesia, yet there is great variation in pain ratings among veterinarians. Women and more recent graduates generally tended to rate pain more highly and treat it more frequently (Dohoo & Dohoo, 1996; Lascelles et al., 1999; Raekallio et al., 2003; Williams et al., 2005; Huxley, 2006;

Laven et al., 2009) and increased usage of analgesics among newer veterinarians may well be due to the changes in emphasis of the treatment of pain that have taken place in veterinary medicine during the past 10–15 years (Thomsen et al., 2010). Although the vast majority of respondents generally agree that provision of analgesia is beneficial, and that animals recover more quickly postoperatively if analgesia is provided, the myth still persists that postoperative pain provides some benefit in preventing animals from being too active (Raekallio et al., 2003; Guatteo et al., 2008), even among veterinarians who graduated in the 2000s (Thomsen et al., 2010)—

despite the position, held since 1998, of the American College of Veterinary Anesthesiologists that unrelieved pain provides no benefits to animals (ACVA, 1998). Even where a large majority of respondents agree about the importance of treating pain, there is much variation in the circumstances under which pain is treated (Hellyer et al., 1999; Hugonnard et al., 2004; Whay & Huxley, 2005).

Data from repeat Canadian surveys were somewhat encouraging.

A 1994 survey showed that approximately 50% of Canadian veterinarians did not use analgesics postoperatively in dogs and cats (Dohoo & Dohoo, 1996). Usage among the other 50% varied with the procedure, and opioids were used almost exclusively, predom- inantly butorphanol. A similar survey in 2001 showed a marked increase in analgesic usage, with only about 12% of Canadian veterinarians not using analgesics (Hewson et al., 2006b). Given, however, the low usage of perioperative analgesics for many surgeries, together with a continued overreliance on weak opioids (e.g., butorphanol, meperidine) and under usage of strong opioids and NSAIDs, it was evident that postoperative pain was not being man- aged effectively much of the time.

In the 1994 survey, pain perception scores attributed to different surgical procedures were one of two primary factors affecting analgesic usage (the second was concern about the use of potent opi- oid agonists in the postoperative period) (Dohoo & Dohoo, 1996).

Perception of pain was also a strong predictor of postoperative analgesic usage in 2001 (Hewson et al., 2006a); ratings of pain caused by different surgeries had increased markedly since 1994.

In both surveys, veterinarians identified lectures and seminars at the regional level, as well as review articles, as the preferred way to receive continuing education regarding pain and analgesia.

PAINFUL HUSBANDRY PRACTICES IN FARM ANIMALS

The use of at least some degree of perioperative analgesia is fairly widespread in small animal practice (Lascelles et al., 1999;

Hugonnard et al., 2004; Hewson et al., 2006b), even if consistency is lacking and there is much room for improvement to provide truly effective, multimodal analgesia. The same cannot be said

with large animals, where it remains customary to perform many procedures without anesthesia or analgesia, particularly in North America (Hewson et al., 2007b; Fulwider et al., 2008). However, in some countries analgesia is legally required when carrying out certain husbandry procedures. For example, all the Scandinavian countries now have regulations governing the use of anesthesia and analgesia for procedures such as dehorning and castrating calves (Thomsen et al., 2010). In New Zealand, analgesia is required for castration of cattle over 6 months and for dehorning in those over 9 months (Laven et al., 2009).

Surveys that have compared attitudes toward, and frequency of, pain alleviation in different species pointed out large differences among different animal species undergoing similar operations and among clinical conditions that received equal pain ratings (Hellyer et al., 1999; Raekallio et al., 2003). Even though there is no physiological basis for this differentiation, the discrepancy between practice in companion and production animals is pronounced (Stookey, 2005).

Roadblocks to Treating Pain in Farm Animals

There are many practices carried out routinely in the management of livestock and poultry that cause pain and distress (e.g., castration, tail docking, dehorning, branding, beak trimming). Many of these husbandry procedures are carried out on very young animals (e.g., tail docking in piglets and lambs, beak trimming in poultry); yet there is mounting evidence that such tissue damage early in life may program the animal to a lasting state of somatosensory sensitization and increased pain (Vi˜nuela-Fern´andez et al., 2007).

Cost–benefit analyses of performing such procedures as an aid to management have too often ignored the costs to the animals themselves in terms of pain and suffering (Hewson, 2006). Increas- ingly, the public expects pain relief to be provided to farm animals (Phillips et al., 2009; Whay & Main, 2009), yet there are economic, practical, and regulatory constraints, such as the cost of treatment relative to the monetary value of the individual animal, limited availability of licensed analgesic drugs in food animals, and concern about drug residues and food safety (Vi ˜nuela-Fern´andez et al., 2007; Mellor et al., 2008a).

In considering a harm/benefit analysis of husbandry procedures, we should first attempt to minimize the harm (Weary et al., 2006) by asking questions such as:

1. Is the procedure necessary? Is it justified in terms of direct benefit to the animals and/or to the farming enterprise? For example hot iron branding is a cause of avoidable pain to animals and yet, since 2005, a US trade rule has required that all feeder cattle entering the United States from Canada be branded, despite the fact that Canadian cattle for export already bear an ear tag traceable to the farm of origin through the Canadian Cattle Iden- tification infrastructure (Whiting, 2005). Is there another way of achieving the same end, for example, the development of polled breeds to eliminate the need for dehorning calves or immunocas- tration in calves, piglets, and lambs (Stafford & Mellor, 2009)?

2. What harms are caused, how bad are they, can they be avoided or reduced (e.g., through treatment of pain)?

3. What are the availability, cost, effectiveness, and ease of administration of pain-relieving drugs? Are there adverse effects or residues? Is administration by a veterinarian required?

(22)

6 Section 1 / Introduction and Anatomy, Physiology, and Pathophysiology of Pain Husbandry practices with no benefits for animals or farmers may

become entrenched. For example, studies have shown no benefits of tail docking in dairy cows, and yet this practice, which has been shown to cause acute and chronic pain, as well as increased fly num- bers, and to which the American and Canadian Veterinary Medi- cal Associations are officially opposed (AVMA, 2009, CVMA, 2010), is still widespread in the United States (Fulwider et al., 2008).

The recognition of pain in species such as cattle and sheep may be more difficult because, as prey species, there was strong evolutionary pressure to mask signs of pain and associated weak- ness (Phillips, 2002; Rutherford, 2002). A large European survey describing pain management practices in cattle (Guatteo et al., 2008) showed very high variability among veterinarians in the knowledge of and sensitivity to pain in cattle. Again, awareness of and ability to assess an animal’s pain were critical to the deci- sion on whether to treat pain. In a similar survey in the United Kingdom, cattle practitioners who did not use analgesics assigned significantly lower pain scores to painful procedures or conditions (Huxley, 2006).

In such studies, veterinarians expressed the concern that pro- ducers would be unwilling to pay additional costs of providing analgesia (Whay et al., 2005; Huxley, 2006; Hewson et al., 2007a;

Guatteo et al., 2008). However, a follow-up study (Huxley & Whay, 2007) showed that, for a significant minority of cattle farmers, the cost of providing analgesia may not be a barrier. For castration and dehorning, for example, 40% and 25% of respondents, respectively, were prepared to pay additional fees sufficient to cover the cost of appropriate analgesic drugs (local anesthesia and NSAIDs).

Fifty-three percent of farmers surveyed agreed with the statement

“Veterinary surgeons do not discuss controlling pain in cattle with farmers enough.”

As well, there are costs to NOT providing analgesia. Apart from causing animal suffering, pain can cause significant economic losses (Denaburski & Tworkowska, 2009; Whay & Main, 2009;

Grandin, 2009). Yet, a UK study (Leach et al., 2010) showed that, despite a high prevalence of lameness in dairy cows (36% in farms surveyed in 2006–2007), the majority of farmers did not perceive lameness to be a problem on their farm, and underestimated the cost of pain to production.

Management of pain is dependent on the stockperson (or animal caregiver) and the veterinarian. Effective pain management requires recognition of the pain, provision of an environment where the animal can recover, and knowledge about and provision of appropriate analgesic drugs. The ways in which an animal is handled and cared for can exacerbate or mitigate pain and distress. Studies in all major farm animal species have confirmed a strong relationship between the methods used in handling animals, the degree of fear the animals show toward people, and the productivity of the farm (Rushen

& Passill´e, 2009). For example, a large study of US dairy farms showed lower somatic cell counts in the milk and tendencies to lower percentages of lame cows and shorter calving intervals on farms where the cows were more willing to approach the observer (Fulwider et al., 2008).

A special issue of Applied Animal Behaviour Science, “Pain in Farm Animals,” summarizes current knowledge about addressing many of the major causes of such pain, for example, disbudding and dehorning in cattle (Stafford & Mellor, 2011a), castration in pigs and other livestock (Sutherland & Tucker, 2011), identification and

prevention of intra- and postoperative pain (Walker et al., 2011), and pain issues in poultry (Gentle, 2011).

THE WAY FORWARD

There have been many advances in the understanding of and ability to treat pain in animals in recent decades. We have the knowledge to effectively manage perioperative pain through multimodal analgesia and there are practical resources available to assist veterinarians to do so (Tranquilli et al., 2004; Cracknell, 2007; Flecknell et al., 2007; Lemke & Crook, 2011). There are published recommendations for managing painful procedures in large animals (Lemke et al., 2008; Stafford & Mellor, 2011b), although there are still many constraints. The management of chronic pain continues to present a challenge.

The widespread finding that a veterinarian’s perception of pain is a significant predictor of analgesic usage is a major concern, especially considering pain ratings vary so markedly. A persuasive case is made in pediatric medicine against allowing personal beliefs about the experience of pain to prevent “optimal recognition and treatment of pain for all children” (Hagen et al., 2001). Veterinary practitioners must adopt the same approach for animals.

Veterinarians commonly feel their knowledge of issues related to recognition and management of pain is inadequate, and are inter- ested in continuing education opportunities to address this lack.

There is a great deal of information available on assessment and management of pain, which needs to be better communicated to veterinary students and veterinarians.

So what can veterinarians do to better manage pain in animals?

Veterinarians working with all species should avail themselves of continuing education regularly to ensure they have current knowledge about recognizing, assessing, and managing pain. Veterinar- ians working with large animals should ensure that they inform farmers of the strategies available to mitigate pain associated with production practices and with chronic conditions, and of the resulting benefits to the animal and to the bottom line. And veterinarians, as a profession, can work with other stakeholders, as expected of them by society as advocates for animals, to address regulatory, technological, and economic constraints.

REFERENCES

ACVA (1998) American college of veterinary anesthesiologists’ posi- tion paper on the treatment of pain in animals. Journal of the Amer- ican Veterinary Medical Association, 213(5), 628–630.

AVMA (2009) Tail Docking of Cattle [Homepage of the American Veterinary Medical Association], http://www.avma.org/

issues/policy/animal_welfare/tail_docking_cattle.asp (accessed July 24, 2013).

AVMA (2011) Animal Welfare Policies [Homepage of the Amer- ican Veterinary Medical Association], https://www.avma.org/KB/

Policies/Pages/Pain-in-Animals.aspx (accessed July 24, 2013).

Bermond, B. (2001) A neuropsychological and evolutionary approach to animal consciousness and animal suffering. Animal Welfare, 10, S47–S62.

Capner, C.A., Lascelles, B.D.X., & Watermann-Pearson, A. (1999) Current British veterinary attitudes to perioperative analgesia for dogs. Veterinary Record, 145(4), 95–99.

Cracknell, J. (2007) Analgesia in Exotics: A Review and Update, British Veterinary Zoological Society, Romford, UK.

(23)

1 / Introduction: Pain: An Issue of Animal Welfare 7 CVMA (2010) Tail Docking of Dairy Cattle [Homepage of

the Canadian Veterinary Medical Association], http://www.

canadianveterinarians.net/documents/tail-docking-of-dairy-cattle#.

UfANWG0U0ms (accessed July 24, 2013).

CVMA (2007) Pain Control in Animals [Homepage of the Canadian Veterinary Medical Association], http://www.

canadianveterinarians.net/documents/pain-control-in-animals#.

UfAN3W0U0ms (accessed July 24, 2013).

Denaburski, J. & Tworkowska, A. (2009) The problem of pain in farm animals and its effects on animal welfare and certain economic results. Polish Journal of Veterinary Sciences, 12(1), 123–131.

Dohoo, S.E. & Dohoo, I.R. (1996) Postoperative use of analgesics in dogs and cats by Canadian veterinarians. The Canadian Veterinary Journal. La Revue V´et´erinaire Canadienne, 37(9), 546–551.

Farm Animal Welfare Council (2009) Five Freedoms [Homepage of FAWC], http://www.fawc.org.uk/freedoms.htm (accessed July 24.

2013).

Flecknell, P., Gledhill, J., & Richardson, C. (2007) Assessing animal health and welfare and recognising pain and distress. ALTEX, 24, Spec No 82–83.

Flower, F.C., Sedlbauer, M., Carter, E., von Keyserlingk, M.A., Sander- son, D.J., & Weary, D.M. (2008) Analgesics improve the gait of lame dairy cattle. Journal of dairy science, 91(8), 3010–3014.

F¨ollmi, J., Steiger, A., Walzer, C., et al. (2007) A scoring system to evaluate physical condition and quality of life in geriatric zoo mammals. Animal Welfare, 16(3), 309–318.

Fulwider, W.K., Grandin, T., Rollin, B.E., Engle, T.E., Dalsted, N.L.,

& Lamm, W.D. (2008) Survey of dairy management practices on one hundred thirteen north central and northeastern United States dairies. Journal of dairy science, 91(4), 1686–1692.

Gentle, M.J. (2001) Attentional shifts alter pain perception in the chicken. Animal Welfare, 10, S187.

Gentle, M.J. (2011) Pain issues in poultry. Applied Animal Behaviour Science, 135(3), 252–258.

Grandin, T. (2009) The Importance of Measurement to Improve the Welfare of Livestock, Poultry and Fish, CABI, Wallingford, UK.

Guatteo, R., Holopherne, D., Whay, H.R., & Huxley, J.N. (2008).

Attitudes et pratiques actuelles des v´et´erinaires praticiens dans la prise en charge de la douleur des bovins [Attitudes and practices of veterinary practitioners in the management of pain in cattle]. Bulletin des GTV, 44, 57–64.

Hagen, J.F., Coleman, W.L., Foy, J.M., et al. (2001) The assessment and management of acute pain in infants, children, and adolescents.

Pediatrics, 108(3), 793.

Heleski, C.R. & Zanella, A.J. (2006) Animal science student attitudes to farm animal welfare. Anthrozo¨os, 19(1), 3–16.

Hellyer, P.W., Frederick, C., Lacy, M., Salman, M.D., & Wagner, A.E. (1999) Attitudes of veterinary medical students, house offi- cers, clinical faculty, and staff toward pain management in animals.

Journal of the American Veterinary Medical Association, 214(2), 238–244.

Hewson, C.J. (2006) “Eat well, spend less.” The costs of cheap food to animals and humans. Canadian Veterinary Journal, 47(1), 38–41.

Hewson, C.J., Dohoo, I.R., & Lemke, K.A. (2006a) Factors affecting the use of postincisional analgesics in dogs and cats by Canadian veterinarians in 2001. Canadian Veterinary Journal, 47(5), 453–459.

Hewson, C.J., Dohoo, I.R., & Lemke, K.A. (2006b) Perioperative use of analgesics in dogs and cats by Canadian veterinarians in 2001.

Canadian Veterinary Journal, 47(4), 352–359.

Hewson, C.J., Dohoo, I.R., Lemke, K.A., & Barkema, H.W. (2007a) Factors affecting Canadian veterinarians’ use of analgesics when

dehorning beef and dairy calves. Canadian Veterinary Journal, 48(11), 1129–1136.

Hewson, C.J., Dohoo, I.R., Lemke, K.A., & Barkema, H.W. (2007b) Canadian veterinarians’ use of analgesics in cattle, pigs, and horses in 2004 and 2005. The Canadian Veterinary Journal. La Revue V´et´erinaire Canadienne, 48(2), 155–164.

Hugonnard, M., Leblond, A., Keroack, S., Cadore, J., & Troncy, E.

(2004) Attitudes and concerns of French veterinarians towards pain and analgesia in dogs and cats. Veterinary Anaesthesia & Analgesia, 31(3), 154–163.

Huxley, J.N. & Whay, H.R. (2006) Current attitudes of cattle practi- tioners to pain and the use of analgesics in cattle. The Veterinary Record, 159(20), 662–668.

Huxley, J.N. & Whay, H.R. (2007) Attitudes of UK veterinary surgeons and cattle farmers to pain and the use of analgesics in cattle. Cattle Practice, 15(2), 189–193.

IASP (1994) Pain terms, a current list with definitions and notes on usage in Classification of Chronic Pain, 2nd edn (eds H. Merskey &

N. Bogduk), IASP Press, Seattle, WA, pp. 209–214.

Johnson, C.B. (2008) Lessons learned from pain management in humans, in Scientific Assessment and Management of Animal Pain, (eds D.J. Mellor, P.M. Thornber, D. Bayvel, et al.), OIE (World Organisation for Animal Health), Paris, pp. 184–194.

Kielland, C., Skjerve, E., & Zanella, A.J. (2009) Attitudes of veterinary students to pain in cattle. Veterinary Record, 165(9), 254–258.

Lascelles, B.D.X., Capner, C.A., & Watermann-Pearson, A. (1999) Current British veterinary attitudes to perioperative analge- sia for cats and small mammals. Veterinary Record, 145(21), 601–604.

Laven, R.A., Huxley, J.N., Whay, H.R., & Stafford, K.J. (2009) Results of a survey of attitudes of dairy veterinarians in New Zealand regard- ing painful procedures and conditions in cattle. New Zealand Veteri- nary Journal, 57(4), 215–220.

Leach, K.A., Whay, H.R., Maggs, C.M., et al. (2010) Working towards a reduction in cattle lameness: 1. Understanding barriers to lameness control on dairy farms. Research in Veterinary Science, 89(2), 311–

317.

Lemke, K.A. & Crook, A.D. (2011) Examples of Anaesthetic and Pain Management Protocols for Healthy Cats and Dogs, 2nd edn [Homepage of the Canadian Veterinary Medical Association], http://www.upei.ca/awc/files/awc/English%20poster%20indiv.

panels_0.pdf (accessed July 24, 2013).

Lemke, K.A., Hewson, C.J., & Crook, A.D. (2008) Examples of Anaesthetic and Pain Management Protocols for Large Animals [Homepage of the Canadian Veterinary Medical Association], http://www.upei.ca/awc/files/awc/Poster%20ENG%203%20Sep%

20Pages.pdf (accessed July 24, 2013).

Levine, E.D., Mills, D.S., & Houpt, K.A. (2005) Attitudes of veterinary students at one US college toward factors relating to farm animal welfare. Journal of Veterinary Medical Education, 32(4), 481–490.

Mathews, K.A. (2000) Pain assessment and general approach to man- agement. The Veterinary Clinics Of North America Small Animal Practice, 30(4), 729.

McMillan, F.D. (2003) Maximizing quality of life in ill animals. Jour- nal of the American Animal Hospital Association, 39(3), 227–235.

Mellor, D.J., Fisher, M.W., & Stafford, K.J. (2008) A Cost-benefit Analysis of Pain Relief for Farm Animals, in Scientific Assessment and Management of Animal Pain, (eds D.J. Mellor, P.M. Thornber, D. Bayvel, et al.), OIE (World Organisation for Animal Health), Paris, pp. 47–55.

(24)

8 Section 1 / Introduction and Anatomy, Physiology, and Pathophysiology of Pain Mellor, D.J., Thornber, P.M., Bayvel, D., & Kahn, S. (2008) Scientific

Assessment and Management of Animal Pain, OIE (World Organi- sation for Animal Health), Paris.

Melzack, R. (1993) Pain: past, present and future. Canadian Journal of Experimental Psychology, 47(4), 615.

Morton, C.M. (2005) Application of a scaling model to establish and validate an interval level pain scale for assessment of acute pain in dogs. American Journal of Veterinary Research, 66(12), 2154–2166.

Phillips, C. (2008) Pain As An Animal Welfare Issue, in Scientific Assessment and Management of Animal Pain, (eds D.J. Mellor, P.M. Thornber, D. Bayvel, et al.), OIE (World Organisation for Ani- mal Health), Paris, pp. 38–46.

Phillips, C. (2002) Environmental perception and cognition in Cattle Behaviour and Welfare, 2nd edn (ed. C. Phillips), Blackwell Science, Oxford, pp. 49–61.

Phillips, C.J., Wojciechowska, J., Meng, J., & Cross, N. (2009) Per- ceptions of the importance of different welfare issues in livestock production. Animal, 3(8), 1152–1166.

Raekallio, M., Heinonen, K.M., Kuussaari, J., & Vainio, O. (2003) Pain alleviation in animals: attitudes and practices of Finnish veterinari- ans. Veterinary Journal, 165(2), 131–135.

Roughan, J.V. & Flecknell, P.A. (2003) Evaluation of a short duration behaviour-based post-operative pain scoring system in rats. Euro- pean Journal of Pain (London, England), 7(5), 397–406.

Rushen, J. & Passill´e, A.M.D. (2009) The Importance of Good Stock- manship and Its Benefits for the Animals, CABI, Wallingford, UK.

Rutherford, K.M.D. (2002) Assessing pain in animals. Animal Welfare, 11, 31–53.

Stafford, K.J. & Mellor, D.J. (2009) Painful Husbandry Procedures in Livestock and Poultry, CABI, Wallingford, UK.

Stafford, K.J. & Mellor, D.J. (2005) The welfare significance of the castration of cattle: a review. New Zealand Veterinary Journal, 53(5), 271–278.

Stafford, K.J. & Mellor, D.J. (2011) Addressing the pain associated with disbudding and dehorning in cattle. Applied Animal Behaviour Science, 135(3), 226–231.

Stookey, J.M. (2005) The veterinarian’s role in controlling pain in farm animals. The Canadian Veterinary Journal. La Revue V´et´erinaire Canadienne, 46(5), 453.

Sutherland, M.A. & Tucker, C.B. (2011) The long and short of it: a review of tail docking in farm animals. Applied Animal Behaviour Science, 135(3), 179–191.

Thomsen, P.T., Gidekull, M., Herskin, M.S., et al. (2010) Scandina- vian bovine practitioners’ attitudes to the use of analgesics in cattle.

Veterinary Record, 167(7), 256–258.

Tranquilli, W.J., Grimm, K.A., & Lamont, L.A. (2004) Pain Manage- ment for the Small Animal Practitioner, 2nd edn, Teton NewMedia, Jackson, WY.

Vickers, K.J., Niel, L., Kiehlbauch, L.M., & Weary, D.M. (2005) Calf response to caustic paste and hot-iron dehorning using sedation with

and without local anesthetic. Journal of Dairy Science, 88(4), 1454–

1459.

Vi˜nuela-Fern´andez, I., Jones, E., Welsh, E.M., & Fleetwood-Walker, S.M. (2007) Pain mechanisms and their implication for the manage- ment of pain in farm and companion animals. Veterinary Journal 174(2), 227–239.

Walker, K.A., Duffield, T.F., & Weary, D.M. (2011) Identifying and preventing pain during and after surgery in farm animals. Applied Animal Behaviour Science, 135(3), 259–265.

Weary, D.M. & Fraser, D. (2008) Identifying Pain in Farm Animals, in Scientific Assessment and Management of Animal Pain, (eds D.J.

Mellor, P.M. Thornber, D. Bayvel, et al.), OIE (World Organisation for Animal Health), Paris, pp. 157–171.

Weary, D.M., Niel, L., Flower, F.C., & Fraser, D. (2006) Identifying and preventing pain in animals. Applied Animal Behaviour Science, 100(1–2), 64–76.

Webster, A.B. & Fletcher, D.L. (2004) Assessment of the aversion of hens to different gas atmospheres using an approach-avoidance test.

Applied Animal Behaviour Science, 88(3), 275–287.

Whay, H.R., Webster, A.J., & Waterman-Pearson, A.E. (2005) Role of ketoprofen in the modulation of hyperalgesia associ- ated with lameness in dairy cattle. Veterinary Record, 157(23), 729–733.

Whay, H.R. & Huxley, J.N. (2005) Pain relief in cattle: a practitioner’s perspective. Cattle Practice, 13(2), 81–85.

Whay, H.R. & Main, D.C.J. (2009) Improving Animal Welfare: Prac- tical Approaches for Achieving Change, CABI, Wallingford, UK.

Whiting, T.L. (2005) Hot iron branding - not a reasonable require- ment for international trade in live ruminants. Canadian Veterinary Journal, 46(11), 1042–1046.

Williams, V.M., Lascelles, B.D.X., & Robson, M.C. (2005) Current attitudes to, and use of, peri-operative analgesia in dogs and cats by veterinarians in New Zealand. New Zealand Veterinary Journal, 53(3), 193–202.

Wiseman-Orr, M., Nolan, A.M., Reid, J., & Scott, E.M. (2004) Devel- opment of a questionnaire to measure the effects of chronic pain on health-related quality of life in dogs. American Journal of Veterinary Research, 65(8), 1077–1084.

Wiseman-Orr, M., Scott, E.M., Reid, J., et al. (2006) Validation of a structured questionnaire as an instrument to measure chronic pain in dogs on the basis of effects on health-related quality of life. American Journal of Veterinary Research, 67(11), 1826–1836.

Wojciechowska, J.I., Hewson, C.J., Stryhn, H., Guy, N.C., Patronek, G.J, Timmons, V. (2005) Development of a discriminative questionnaire to assess nonphysical aspects of quality of life of dogs.

American Journal of Veterinary Research, 66(8), 1453–1460.

Yazbek, K.V.B. & Fantoni, D.T. (2005) Validity of a health-related quality-of-life scale for dogs with signs of pain secondary to cancer.

Journal of the American Veterinary Medical Association, 226(8), 1354–1358.

(25)

2 Anatomy, Physiology, and Pathophysiology of Pain

Yael Shilo and Peter J. Pascoe

Pain in animals has been defined as “an aversive sensory and emotional experience representing an awareness by the animal of damage or threat to the integrity of its tissues; it changes the animal’s physiology and behavior to reduce or avoid damage, to reduce the likelihood of recurrence, and to promote recovery” (Molony &

Kent, 1997).

The ability to react to environmental change is crucial for the survival of an organism, and an essential prerequisite is the capac- ity to detect and respond to aversive stimuli. Primary afferent nerve fibers provide information to the central nervous system (CNS) about the environment and also about the state of the organism itself. Incoming non-noxious input from the periphery is important for discerning fine discriminative touch, pressure, and position in space. Most animals have dedicated sensory afferents that respond to noxious stimuli. These nociceptive afferents are described by the International Association for the Study of Pain (IASP) as “preferen- tially sensitive to a noxious stimulus or to a stimulus which would become noxious if prolonged” (Wall et al., 2006; Smith & Lewin, 2009). Information about a noxious event in the periphery can initiate a protective reflexive withdrawal event (Westlund, 2005; Smith

& Lewin, 2009).

Nociception, derived from the Latin nocere meaning “to hurt/harm,” is the name given to the process by which organisms detect potentially or actually damaging stimuli and the transmission of that information to the brain. It is important to differentiate nociception from pain, which always encompasses an emotional component. Nociceptor activation in and of itself does not neces- sarily result in pain (Julius & Basbaum, 2001; Muir & Woolf, 2001;

Smith & Lewin, 2009; Basser, 2012).

Noxious input is transmitted to the brain through specialized receptors, fibers, and neurons, and processing occurs at many levels (Figure 2.1). Sensory processing includes

Transduction: the conversion of noxious stimuli into an action potential at the level of the specialized receptors or free nerve endings.

Transmission: the propagation of the action potentials by primary afferent neurons to the spinal cord.

Modulation: the process by which nociceptive information is aug- mented or inhibited.

Projection : the conveyance of nociceptive information through the spinal cord to the brain (to the brainstem and thalamus and then to the cortex).

Perception: the integration of the nociceptive information by the brain, or, in other words, the overall conscious, emotional experience of pain (Muir & Woolf, 2001; Westlund, 2005; Muir, 2009).

NOCICEPTORS

Activation of nociceptors requires that adequate stimuli depolarize peripheral terminals (producing a receptor potential) with sufficient amplitude and duration. This ensures that despite any attenuation and slowing of the action potential (by passive propagation), information such as stimulus intensity will be encoded in the resulting train of impulses (Dubin & Patapoutian, 2010).

Nociceptive neurons that detect chemical stimuli have a distinct expression of ion channel systems or transduction channels, including transient receptor potential (TRP) ion channels, acid-sensing ion channels (ASIC), purinoceptors, serotonin receptors, and sodium, calcium, and potassium channels (Wall et al., 2006). Agents such as protons or capsaicin directly depolarize nociceptive neurons by triggering the opening of cation channels permeable to sodium and/or calcium. In contrast, agents such as bradykinin and nerve growth factor (NGF) act on G protein-coupled receptors and receptor tyrosine kinase, respectively, to initiate intracellular signaling cascades that, in turn, sensitize depolarizing cation channels to their respective physical or chemical regulators. Other agents, such as glutamate, acetylcholine (ACh), and adenosine triphosphate (ATP), activate ion channels and G-protein-coupled receptors to produce a spectrum of direct and indirect effects on nociceptor membrane potentials (Caterina et al., 2005). This chapter will focus on several important transduction channels; however, it is beyond the scope of this chapter to discuss all of these.

Transient Receptor Potential Ion Channel

The TRPs have emerged as a family of principal transducing channels on sensory neurons, and are classified according to their primary amino acid sequence (rather than according to their selectivity or ligand affinity), as their properties are heterogeneous and their

9