Diagnostic Techniques in Equine Medicine. A textbook for students and practitioners describing diagnostic techniques applicable to the adult horse

382 Pages·12.412 MB·English

by  Dr Frank GR Taylor, BVSc PhD MRCVS, Dr Tim J Brazil, BVSc PhD CertEM (Int Med) DECEIM MRCVS, and Dr Mark H Hillyer, BVSc DipECVS PhD DipECEIM CertEP CertES (soft Tissue) CertEM (Int Med) MRCVS (Eds.)

Dedication
To my wife Sabine and our children Anna,
James and Max, for their forbearance during
the preparation of this book.
Frank Taylor
Commissioning Editor: Robert Edwards
Development Editor: Nicola Lally
Project Manager: Emma Riley and K Anand Kumar
Designer/Design Direction: Charles Gray
Illustration Manager: Bruce Hogarth
Illustrator: Samantha Elmhurst
First edition © WB Saunders Company Ltd 1997
Second edition © 2010, Elsevier Limited. All rights reserved.
No part of this publication may be reproduced or transmitted in any form or by any means, electronic
or mechanical, including photocopying, recording, or any information storage and retrieval system,
without permission in writing from the publisher. Permissions may be sought directly from Elsevier’s
Rights Department: phone: [phone] (US) or ([phone] (UK); fax: (+44) 1865
853333; e-mail: [email protected]. You may also complete your request online via the
Elsevier website at http://www.elsevier.com/permissions.
ISBN 978-0-7020-2792-5
British Library Cataloguing in Publication Data
A catalogue record for this book is available from the British Library
Library of Congress Cataloging in Publication Data
A catalog record for this book is available from the Library of Congress
Notice
Knowledge and best practice in this field are constantly changing. As new research and experience
broaden our knowledge, changes in practice, treatment and drug therapy may become necessary or
appropriate. Readers are advised to check the most current information provided (i) on procedures
featured or (ii) by the manufacturer of each product to be administered, to verify the recommended dose
or formula, the method and duration of administration, and contraindications. It is the responsibility of
the practitioner, relying on their own experience and knowledge of the patient, to make diagnoses, to
determine dosages and the best treatment for each individual patient, and to take all appropriate safety
precautions. To the fullest extent of the law, neither the Publisher nor the Editors assumes any liability for
any injury and/or damage to persons or property arising out of or related to any use of the material
contained in this book.
The Publisher
The
Working together to grow
publisher’s
libraries in developing countries policy is to use
paper manufactured
from sustainable forests
www.elsevier.com | www.bookaid.org | www.sabre.org
Printed in China
CONSULTING AUTHORS
Chapter 1: Submission of laboratory samples and Dr Grant S Frazer BVSc MS DipACT
interpretation of results
Associate Professor of Theriogenology & Reproductive
Professor Sidney Ricketts LVO BSc BVSc DESM DipECEIM Medicine, Department of Veterinary Clinical Sciences,
FRCPath FRCVS College of Veterinary Medicine, The Ohio State University,
Rossdale & Partners, Beaufort Cottage Laboratories, High Columbus, Ohio, USA
Street, Newmarket, Suffolk, UK
Chapter 8: Blood disorders
Chapter 2: Alimentary diseases Professor Michelle Barton DVM PhD DipACVM
Professor Anthony T Blikslager DVM PhD DipACVS Department of Large Animal Medicine, University of
Equine Surgery & Gastrointestinal Biology, North Carolina Georgia, Athens, Georgia, USA
State University, Raleigh, North Carolina, USA
Chapter 9: Cardiovascular diseases
Chapter 3: Chronic wasting Dr Lesley E Young BVSc PhD DipECEIM DVC MRCVS
Kristopher J Hughes BVSc FACVSc DipECEIM MRCVS Specialist Equine Cardiology Services, Ousden, Newmarket,
Professor Sandy Love BVMS PhD MRCVS Suffolk, UK
Division of Companion Animal Sciences, Faculty of
Veterinary Medicine, University of Glasgow, Glasgow, UK Chapter 10: Lymphatic diseases
Amanda M House DVM DACVIM
Chapter 4: Liver diseases Assistant Professor, Large Animal Clinical Sciences,
Mr Andrew Durham BSc BVSc CertEP DEIM DipECEIM MRCVS University of Florida College of Veterinary Medicine,
Gainesville, Florida, USA
The Liphook Equine Hospital, Forest Mere, Liphook, Hants,
UK
Chapter 11: Fluid, electrolyte and acid–base balance
Chapter 5: Endocrine diseases Dr Louise Southwood
Professor Philip J Johnson BVSc MS DipACVIM Assistant Professor, Emergency Medicine & Critical Care,
School of Veterinary Medicine, New Bolton Center,
DipECEIM MRCVS
Philadelphia, Pennsylvania, USA
Professor of Equine Internal Medicine, Department of
Veterinary Medicine & Surgery, College of Veterinary
Medicine, University of Missouri, Columbia, Missouri, USA Chapter 12: Respiratory diseases
Dr TS Mair BVSc PhD DipECEIM DEIM DESTS MRCVS
Chapter 6: Urinary diseases Bell Equine Veterinary Clinic, Mereworth, Maidstone, Kent,
Professor Thomas J Divers DVM DipACVIM DipACVECC UK
Department of Clinical Sciences, College of Veterinary
Medicine, Cornell University, Ithaca, New York, USA Chapter 13: Musculoskeletal diseases
Professor ARS Barr MA VetMB PhD DVR CertSAO DEO
Chapter 7: Genital diseases, fertility and pregnancy DipECVS MRCVS
Dr Carlos RF Pinto Med.Vet PhD DipACT Department of Clinical Veterinary Science, University of
Bristol, Langford House, Langford, North Somerset, UK
Associate Professor of Theriogenology & Reproductive
Medicine, Department of Veterinary Clinical Sciences,
College of Veterinary Medicine, The Ohio State University,
Columbus, Ohio, USA
Consulting authors
Chapter 14: Neurological diseases Chapter 18: Post-mortem examination
Philip AS Ivens MA VetMB Cert EM (Int Med) MRCVS Dr Frank GR Taylor BVSc PhD MRCVS
Richard J Piercy VetMB MA DipACVIM MRCVS Head of the School of Clinical Veterinary Science, University
Comparative Neuromuscular Diseases Laboratory, The Royal of Bristol, Langford House, Langford, North Somerset, UK
Veterinary College, Hawkshead Lane, North Mymms,
Hatfield, Herts, UK Chapter 19: Sudden and unexpected death
Dr Frank GR Taylor BVSc PhD MRCVS
Chapter 15: Ocular diseases
Head of the School of Clinical Veterinary Science, University
Dennis E Brooks DVM PhD DipACVO of Bristol, Langford House, Langford, North Somerset, UK
Professor of Ophthalmology, University of Florida, Dr Tim J Brazil BVSc PhD CertEM (Int Med) DECEIM MRCVS
Gainesville, Florida, USA Equine Medicine on the Move, Moreton-in-Marsh,
Gloucestershire, UK
Chapter 16: Fat diseases
Professor Michel Levy DVM DipACVIM
Associate Professor, Large Animal Internal Medicine, School
of Veterinary Medicine, Purdue University, West Lafayette,
Indiana, USA
Chapter 17: Skin diseases
Hilary Jackson BVM&S DVD DipACVD
Dermatology Referral Service, Glasgow, Lanarkshire, UK
viii
PREFACE
Diagnosis is fundamental to the appropriate treat- We have tried to ensure that the instructions are
ment and wellbeing of the equine patient. Despite sufficiently detailed to allow completion of a proce-
the many excellent clinical texts that are available, dure by following the text. Where appropriate, the
few seem to explain in sufficiently precise terms advantages and disadvantages of a technique receive
which clinicopathological tests are appropriate or brief comment, together with a guide to the inter-
how particular techniques should be performed. pretation of results. For the purpose of practicality
The first edition of this book was designed to provide the techniques are again grouped by chapter on an
an illustrated practical guide to the various diagnos- organ system basis. In addition, a number of chap-
tic techniques employed in equine medicine. This ters have appendices that indicate applications of
second edition is an update by international experts the described techniques to a given set of clinical
in the field. Once again, it predominantly covers the circumstances such as anaemia, polyuria/polydip-
adult horse and is intended for students, recent sia, nasal discharge, etc. The importance of recogniz-
graduates and those veterinarians who do not spe- ing clinical signs is paramount and these are given
cialize in equine work and may therefore be unfa- when relevant.
miliar with some of the diagnostic approaches. We hope that this book will prove useful to prac-
Some of the more specialized techniques made pos- titioners, and beneficial to their patients.
sible by recent advances, notably ultrasound, are
now available to practitioners and figure more Bristol 2009 FGR Taylor
prominently in this edition. TJ Brazil
MH Hillyer
1
CHAPTER
Submission of laboratory samples and
interpretation of results
Chapter contents
I. Submission of laboratory samples 1 Serum enzymes 17
Choice of test 2 Bile acids 19
Suitability of the sample for the Cardiac troponin (cTnI) 19
intended test 2 Blood urea and creatinine 19
Haematology samples 3 Blood glucose 19
Biochemistry samples 4 Serum bilirubin 19
Urine samples 6 Electrolytes 19
Faecal samples 7 Triglycerides 21
Microbiology samples 7 Serum biochemistry profiles 21
Cytopathology samples 8 Interpretation of endocrinological test results 21
Histopathology samples 8 Pregnancy tests 21
Information that should accompany the Cryptorchidism 22
sample 8
Thyroid function 23
Packaging for postal or other delivery 8
Pituitary function 23
Interpretation of urine analysis results 23
II. Interpretation of results 10
Interpretation of parasitological test results 23
Laboratory reference ranges 10
Faecal worm egg counts 23
Interpretation of haematological results 11
Erythrocyte parameters 11
Further reading 24
Leukocyte parameters 12
Plasma fibrinogen concentration 14
APPENDIX 1.1 25
Interpretation of blood biochemical results 14
Haematological and biochemical reference ranges for
Serum proteins 14 adult non-Thoroughbred horses
I. SUBMISSION OF LABORATORY
assist in the systematic deduction of a diagnosis.
SAMPLES
Laboratory investigations are no substitute for a
thorough consideration of the history and clinical
Clinical pathology should be used to help narrow a examination; they are complementary in that they
differential diagnosis, to confirm a diagnosis or to provide further information. However, laboratory
Diagnostic techniques in equine medicine
screening may play a part in preventive medicine can be applied to the different organ systems of the
and performance assessment programmes. horse. From these guidelines the clinician must
Routine clinicopathological investigations select the laboratory tests most likely to confirm or
include the following: refute a diagnosis based upon the history and clini-
• Haematology cal examination. A batch of ill-chosen tests will
• Biochemistry of serum/plasma or other fluids provide little or no information at considerable
• Endocrinology expense. If in any doubt, test selection should be
discussed with a clinical pathologist by telephone.
• Parasitology
Communication between clinician and clinical
• Microbiology
pathologist will only enhance the end result of the
• Cytopathology
investigation.
• Histopathology.
Many practices have or are developing their own
Suitability of the sample for the
laboratory facilities but in many cases it will be
intended test
necessary to forward samples to a more specialized
equine clinical pathology laboratory. One of the An adequate sample volume must be collected into
major limitations to test quality is the suitability of an appropriate container and submitted to the labo-
the sample that is received by the laboratory. Before ratory as quickly as possible. Commercial laborato-
submitting material, several factors should be ries recommend 5 ml anticoagulated samples for
considered: haematological analyses and 10 ml clotted blood
• The choice of test samples for biochemical analyses. Blood samples
• The suitability of the sample for the intended that are haemolysed or lipaemic are unsuitable for
test analysis and those taken from dehydrated horses
• The information that should accompany the must be interpreted carefully, as haematological and
sample serum biochemical parameters may be raised for
• The suitability of packaging for postal or other that reason alone.
delivery. Table 1.1 shows the samples and containers that
are appropriate to particular tests, but the specific
requirements of individual laboratories should be
Choice of test
checked. Some will supply their own preferred con-
Tests must be relevant to and provide information tainers, packaging and labels on request. Two blood
about the implicated organ system or the clinical collection systems are currently in common veteri-
presentation. One of the purposes of this book is to nary use: the Vacutainer (Becton Dickinson) and the
indicate the range of clinicopathological tests that Monovette (Sarstedt) systems (Fig. 1.1 (Plate 1)),
Table 1.1 The two most commonly used blood sampling systems for equine clinical pathology sampling
Test Anticoagulant Monovette (Sarstedt) Vacutainer (BD)
Haematology EDTA 4.5 ml (blue) 10 ml (mauve)
Serum biochemistry, endocrinology None or clot separation 9 ml (brown) 10 ml (red)
beads or gel
Clotting function/plasma fibrinogen Sodium citrate 3 ml (green) 4.5 ml (blue)
Glucose Fluoride oxalate 5.5 ml (yellow) 4.5 ml (grey)
Plasma biochemistry, endocrinology Lithium heparin 9 ml (orange) 10 ml (green)
2
1
Diagnostic techniques in equine medicine Submission of laboratory samples and interpretation of results
should be the one submitted for haematological
examination, in order to minimize the effect of
splenic contraction. If the horse is clearly excited or
has recently been exercised, this should be noted on
the request form to the laboratory. Blood tubes
should be filled to capacity and gently mixed by
several inversions.
If a needle and syringe are used to collect blood,
the following precautions must be observed:
• Blood must not be kept in the syringe for more
than 90 seconds, otherwise clots form
• The needle must be removed from the syringe
before transferring blood into the sample tube,
Figure 1.1 (Plate 1 in colour plate section) Various tubes
suitable for collecting specific blood samples from horses otherwise haemolysis may occur
(see Table 1.1). (Left) Becton Dickinson’s Vacutainers. (Right) • The sample tube must be filled to the indicated
Sarstedt’s Monovettes.
line to maintain the working concentration of
EDTA. An increased concentration causes
with individual clinicians and laboratories having changes in red cell size and inaccurate results,
their own preferences. whereas a decrease predisposes clot formation
• The blood must be mixed with the
Haematology samples anticoagulant by immediate, gentle inversion.
The most suitable anticoagulant for haematological Haematology samples are best processed immedi-
investigations is ethylenediamine tetra-acetic acid ately but for short-term storage the tube should be
(EDTA). Heparin may cause ‘clumping’ of leuko- kept cool. Refrigeration at 4°C is not recommended
cytes and alter their staining properties. Plasma for equine blood samples. An air-dried smear should
fibrinogen estimation can be undertaken using an be prepared soon after sampling, because prolonged
EDTA sample, but only if the laboratory employs a contact with EDTA can alter cell morphology and
heat precipitation technique. The more accurate leukocytes can become difficult to identify. The
thrombin coagulation estimation requires blood to smear can be dispatched to the laboratory in the
be submitted in sodium citrate anticoagulant. Blood unstained state, together with the parent blood
coagulation studies (e.g. prothrombin time; partial sample. Special slide holders can be supplied for this
thromboplastin time) require whole blood to be purpose (Fig. 1.2). However, in most cases well-
submitted in sodium citrate. It is wise to collect packaged equine blood samples that have been care-
blood samples into three tubes for general equine fully collected into EDTA and properly mixed will
clinical pathology purposes: travel well for next-day delivery to the laboratory.
• EDTA for haematological studies Most problems occur in hot weather and when
samples are delayed for more than 24 hours in the
• Sodium citrate for plasma fibrinogen estimation
post.
• Empty or clot separation bead tube for serum
biochemical studies.
Preparation of a blood smear
If blood glucose estimation is required then an addi-
tional sample should be collected into fluoride The glass slides used for smear preparation must be
oxalate anticoagulant. scrupulously clean. Ideally, they should be stored in
Blood samples should be collected at rest from spirit and wiped dry with a tissue before use. The
the jugular vein. If possible, the horse should not be sample is well mixed by gentle inversion and a drop
excited, but if this seems likely the first sample taken of blood is placed towards the end of a horizontal
3
Diagnostic techniques in equine medicine
Figure 1.3 Preparing a blood smear.
Biochemistry samples
Samples submitted for biochemical and endocrino-
logical testing may be of serum, plasma or other fluid.
Figure 1.2 Polypropylene slide holders suitable for Serum is preferred by most laboratories for blood
transporting blood smears. biochemical and endocrinological testing and is
essential for certain tests such as serological tests (anti-
body titration), protein electrophoresis and equine
slide by pipette. The short edge of a second slide is
chorionic gonadotrophin (eCG) testing. Although a
used as a spreader and is placed in front of the drop
perceived advantage of plasma is that it is easily sepa-
of blood at an angle of about 40° (Fig. 1.3). It is
rated from whole blood by standing or centrifuging
first drawn gently backwards to make contact with
prior to dispatch, it is unsuitable for some electrolyte
the drop, which is immediately distributed along
and enzyme estimations and does not store satisfacto-
the spreading edge by capillary action. Once evenly
rily. Always send a clotted blood sample if possible.
distributed along this edge, the blood is then
Where plasma is acceptable, the blood should be col-
smeared along the length of the slide by a single,
lected into lithium heparin anticoagulant. Common
steady, forward movement of the spreader. The pre-
container requirements are shown in Table 1.2.
pared smear is then dried quickly by waving it
Whether clotted or heparinized samples are used,
rapidly in air. The slide can be identified by writing
the serum or plasma should be separated from the
across the frosted end or the centre of the dried
clot or red cells as soon as possible to avoid interac-
smear with a pencil; this will not interfere with sub-
tions between the two. Haemolysis may interfere
sequent staining or the differential count.
with the measurement of enzymes, electrolytes and
The technique of smear preparation is easily
minerals. Haemolysis can be minimized by using
acquired but requires a little practice. Poor smears
clean dry equipment, avoiding perivascular blood
are produced by one or more of the following
sampling and not traumatizing the sample during
mistakes:
or after collection. Whole blood samples sent by
• Using dirty slides and/or a chipped spreader
post during extremes of hot or cold weather are
• Using a drop of blood that is too large
particularly prone to haemolysis.
• Using a spreader angle that is insufficiently
acute Serum separation
• Using a forward movement that is too fast An optimal serum yield can be obtained by collect-
• Using a slow, jerky forward movement. ing blood into a plain Monovette or Vacutainer tube,
4
1
Diagnostic techniques in equine medicine Submission of laboratory samples and interpretation of results
Table 1.2 Appropriate samples and containers for clinicopathological tests
Test Sample Container/medium
Haematology
Blood count ± differential Whole blood EDTA
Plasma fibrinogen Labs vary:
Whole blood (heat precipitation) EDTA or heparin
Plasma (thrombin coagulation) Sodium citrate
Coagulation tests PT/PTT Whole blood Sodium citrate
Blood enzymes
Most enzymes Labs vary:
Serum usually preferred Plain glass
Plasma possible Heparin
Glutathione peroxidase Whole blood Heparin
LDH Serum Plain glass
Blood electrolytes
Serum electrolytes Serum preferred Plain glass
Plasma electrolytes possible Heparin
Other biochemistry
Urea Serum (preferred) or plasma Plain glass or heparin
Creatinine Serum (preferred) or plasma Plain glass or heparin
Total protein Serum Plain glass
Albumin (and globulin) Serum Plain glass
Protein electrophoresis Serum Plain glass
Glucose Plasma Oxalate–fluoride
Total bilirubin Serum (preferred) or plasma Plain glass or heparin
Total serum bile acids Serum Plain glass
Serum triglycerides Serum Plain glass
Blood hormones
Cortisol Serum (preferred) or plasma Plain glass or heparin
Thyroxine Serum (preferred) or plasma Plain glass or heparin
Triiodothyronine Serum (preferred) or plasma Plain glass or heparin
Progesterone Serum (preferred) or plasma Plain glass or heparin
Testosterone Serum (preferred) or plasma Plain glass or heparin
Oestradiol Serum (preferred) or plasma Plain glass or heparin
Oestrone sulphate Serum (preferred) or plasma Plain glass or heparin
eCG Serum Plain glass
Continued
5