EQUINE CLINICAL PATHOLOGY - Rossdale & Partners

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T h e B e a u f o r t c o t t a g e l a b o r a t o r i e s necropsy (postmortem) examinations 48 Full necropsy examinations should be performed on all adult and younger horses who die unexpectedly, those who may pose a risk to in-contact horses, or for whom confirmation of pathology is required, and those who are the subject of an insurance claim. Ideally, the examination should be performed, without delay, under conditions of adequate facilities, by suitably qualified and experienced pathologists, so that the end result is satisfactory in terms of answering the questions posed. Nevertheless, for a variety of reasons, it may not always be possible for dead horses to be transported to a specialised equine pathology facility and examinations may need to be performed ‘in the field’. Faced with this need, those responsible should consider what conditions are required to enable a productive examination to be performed. Also, waste and carcase disposal, prevention of environmental contamination and spread of infectious agents to humans and other animals must be considered. Occasionally, it may be possible to refer part of a carcase for specific necropsy investigations, e.g. a foot or a leg only for orthopaedic examinations or the head and neck to thoracic vertebra 3 in cases of ataxia for cervical cord compression examination. Adult horses Where full post-mortem facilities, including hoists and tables are not available, experience suggests that the horse should be positioned on the ground in right lateral recumbency. If an incline is available, the horse’s back should be positioned up the hill. The horse should be identified and an external examination performed and findings recorded. The first cut is made deeply under the left axilla to lay the left front leg upward and flat back over the horse’s withers. The second cut is made deeply under the left groin, aiming caudally towards the anus, through the left hip joint, to lay the left hind leg upwards and flat back over the horse’s pelvis. The abdomen is then opened along the midline, from xiphisternum to pubis and the left abdominal wall is laid back over the horse’s back by cutting up adjacent to the last rib and up into the groin. The caecum, large colon and small intestines are then removed from the abdomen while looking for signs of displacement or gross pathology. The small intestines are removed carefully, examining the cranial mesenteric root for verminous pathology and the pancreas, and taking care not to remove the kidneys and adrenal glands from their attachments below the spine. The spleen, stomach and liver are then removed and examined. The kidneys are then carefully removed for examination to leave the adrenal glands attached either side of the aorta. A block
G u i d e t o e q u i n e c l i n i c a l p a t h o l o g y of tissue is then removed to include both adrenal glands and the adjacent aorta, for overnight fixation, prior to dissecting out the coeliaco-mesenteric sympathetic nerve ganglia, which lie between the adrenal glands and the aorta, but which are less easy to find in fresh condition. The bladder and internal genitalia are then removed and examined. The diaphragm is then examined and opened to reveal the thoracic viscera. The ribs are separated through their costochondral junctions, the intercostal muscles are cut and the ribs are broken back over the horse’s back. The ‘pluck’ including the trachea, heart and lungs are then removed for examination. The thymus is examined and removed in immature horses. The head is removed through the atlanto-occipital joint and ideally sectioned longitudinally with a band saw. The brain, meninges, guttural pouches, paranasal sinuses, teeth, pharynx and larynx are then examined thoroughly. The limb joints are opened for examination of the synovial fluid and surfaces. If indicated by the clinical signs, the neck and back vertebrae are dissected out and opened for examination of their articulations and the spinal cord. It is clear that a satisfactory examination of the head and spine of an adult horse is difficult to achieve under field conditions. Samples for bacterial or viral examination should be collected from abscesses, areas of inflammation, body cavities or seared viscera, using sterile swabs and placed without delay into Amies’ charcoal or specific viral transport media. Fluid samples from abscesses, cysts or body cavity fluids should be aspirated with a sterile syringe and then submitted in sequestrene (EDTA) for a nucleated cell count, and fixed with a suitable fixative (e.g. cytospin fixation fluid) for specific cytological processing. Another undiluted and unfixed sample should be submitted in a sterile container or on a sterile swab in transport medium or ideally into blood culture medium for concurrent bacterial culture. Samples for histopathological processing and examination should be carefully selected to provide thin and small, but representative tissue wedges, and totally immersed in 10% formol saline. Large thick samples fail to fix adequately and histopathological examinations are then unnecessarily complicated by autolytic changes, abused tissues may be ruined by artefactual damage and unrepresentative samples may not include the primary pathological changes. It is often wise to retain appropriate samples, e.g. gastric and intestinal content, urine and cubes of liver and kidney, carefully labelled, frozen, in case toxicological studies are required at a later date. 49
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EQUINE CLINICAL PATHOLOGY - Rossdale & Partners

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