Veterinary Handbook Contents

11.4 Necropsy Findings For Specific Conditions

Gross necropsy is valuable to assist in diagnosing the cause of death in animals that die during the export process. With a diagnosis, or a short list of differential diagnoses, the veterinarian or stockperson is better able to manage the health of the rest of the consignment to prevent more deaths.

11.4.1 Bovine Respiratory Disease (BRD)

Animals with BRD may not have external signs of disease. Note that a frothy white or pink nasal discharge (due to the presence of blood) is not necessarily indicative of BRD. Reddening of the nasal mucosa and muzzle has been reported in feedlot calves with infectious bovine rhinotracheitis (IBR), caused by Bovine Herpesvirus-1, but this has not been reported in export cattle.

The thoracic cavity should be opened completely so that the lungs can be inspected thoroughly. On-board veterinarians may be tempted to examine the lungs through an incision in the diaphragm because this caudal approach to the thoracic cavity means that the ribs don’t have to be removed. However, BRD-associated pneumonia most commonly affects the cranioventral lung fields, which are not easy to see or palpate using a caudal approach to the thoracic cavity. Therefore, the ribs should be removed so that the entire lung fields can be seen and palpated.

Dependent post-mortem fluid redistribution is a common finding in cattle that have been dead for a while. This can affect both the colour and texture of the lung. If possible, necropsy the animal as you find it, rather than turning it over to the standard left side down/right side up orientation.

Palpation is the key to diagnosing BRD. The colour of the lungs and the distribution of discolouration (if present) are often not reliable indicators of the presence or absence of pneumonia. This is particularly true in the case of export cattle, where the animal may have been dead for a number of hours before it is necropsied.

Normal lungs will deflate when the diaphragm is punctured and feel spongy due to air remaining in the alveoli. Normally deflated lungs will be pale pink in colour. If the animal has been dead for a while, post-mortem fluid redistribution may prevent the lungs from deflating normally when the diaphragm is punctured. In this case, the lungs will feel spongy, but also heavy and rubbery. The lungs may be discoloured dark red, grey-pink or grey. The colour and pattern of discolouration of lungs from these animals may be very similar to BRD, but is usually due to congestion or haemorrhage, rather than BRD.

The classic lung lesion for BRD is consolidation of the lung parenchyma in the cranioventral lung fields. Consolidation is also known as ‘hepatisation’ since the texture of the consolidated lung is similar to that of a normal liver. The border between affected and unaffected regions shows a lobular pattern, i.e. some lobules are dark red and consolidated while adjacent lobules are apparently normal.

The interlobular septae may be expanded, resulting in separation of the lobules of affected lung lobes by clear to white material. On cut surface, the lung parenchyma may be shiny and glistening (indicating oedema). Purulent material can be squeezed from small airways, although this may not be possible in severely consolidated regions. In more advanced cases, there is a marbled pattern produced by differing degrees and stages of coagulation, necrosis, and consolidation of lobules, and interlobular oedema and fibrin. There may be concurrent overinflation of the lungs, particularly in the caudodorsal lung fields. This may lead to the formation of subpleural and/or interlobular emphysema and formation of bullae.

If there is bacterial pneumonia there may be a veil of white to yellow fibrin on the surface of the lung. With time, fibrinous attachment may develop between the lung and thoracic wall. The thoracic cavity may contain yellow to orange fluid with clumped fibrin strands.

Laboratory identification of BRD-associated viruses and bacteria requires nasal or lung swabs in transport media. Transport media should be kept frozen until use. Thaw the media just before necropsy, swab the area of interest, place the swab tip in the media, and return the media and sample to the freezer as soon as possible after necropsy.

Two additional patterns of pneumonia (embolic pneumonia and viral pneumonia) warrant mentioning but are rarely seen in export cattle.

In embolic pneumonia there is a random multifocal pattern of discolouration and consolidation, often affecting single lobules or small clusters of lobules. In cattle, embolic pneumonia commonly occurs secondary to endocarditis, hepatic abscess, or phlebitis of hepatic vein, although the source of the emboli cannot always be determined.

Primary viral pneumonia is rarely seen in export cattle. There is grey-red discolouration of the lung in a cranioventral or generalised lobular pattern. The lungs are firm or rubbery texture. There may be mild swelling or atelectasis of lung tissue.

11.4.2 Heat Stress

Heat stress and pneumonia may be difficult to differentiate while the animal is alive. At necropsy, be sure to feel the lungs. Firm, solid consolidated lung tissue is indicative of pneumonia. In cases of heat stress, the lungs are heavy and wet, but still spongy and may be red to dark red due to congestion. The mucosae of the trachea and bronchi are dark red.

At necropsy, the carcass is hot to touch and the eyes are sunken. The muscles are pink rather than the normal brownish-red. The heart is small and tightly contracted with multifocal epicardial haemorrhages (ecchymoses). There is congestion of meningeal blood vessels.

Core body temperatures should be measured using a cooking thermometer as soon after death as possible. In cases of heat stress, core body temperatures are consistently greater than 43.0ºC. Core body temperature normally elevates considerably after death in large, fat, or hairy cattle. However, it usually takes a few hours before the core temperature reaches the levels that may be seen immediately after death from heat stress. It is important to measure core temperature soon after death to avoid erroneously attributing post-mortem elevation of body temperature to heat stress.

Take note of concurrent conditions that may have predisposed the animal to heat stress, e.g. Bos taurus cattle, particularly animals that are fat, or those with long hair coats covered in manure, or concurrent disease conditions such as lameness, pneumonia, or diarrhoea.

11.4.3 Musculoskeletal Injury

In live export cattle, lameness usually develops secondary to leg abrasions or broken bones.

Skin abrasions on the legs are most common in the pastern/fetlock area, but can also occur on the rostral hoof (toe), rostral carpus, lateral elbow, or lateral hock. Swelling of the affected area is visible grossly. On the cut surface, the tissue is discoloured yellow, green or brown, and there may be pus and/or faecal contamination. If you have euthanased the animal for lameness it is worth assessing the lungs as concurrent pneumonia may be detected. Lameness may arise from a secondary bacterial joint infection associated with Bovine Respiratory Disease (BRD).

Bone fractures may be grossly obvious on visual inspection or palpation of the fracture site may cause crepitus (friction from the rough surfaces of a fractured bone rubbing together). Bruising and haematoma will be found on dissection of the soft tissue structures around the fracture site. Fractures may be caused by direct trauma with the pen or loading infrastructure during handling or may result from a misadventure in the pen.

11.4.4 Ketosis

Ketosis is most commonly observed in shipments of pregnant dairy cattle or in consignments of fat lambs. Affected animals usually have normal lungs and no lameness.

In dairy cattle, a strong reaction to ketones in urine or milk on a dipstick test strip is diagnostic for ketosis. The liver is enlarged, pale, yellow or orange, and friable. The kidneys may be similarly affected. The rumen and intestines may be shrunken and fat deposits (especially around the kidneys and heart) may appear jelly-like (serous atrophy). A smaller than normal liver and gall bladder may be present in animals suffering long term reduced food intake.

Differential diagnoses include those causing inappetence and weight loss, such as displaced abomasum and chronic inflammatory conditions such as liver abscess or low grade pneumonia.

11.4.5 Septicaemia

In export stock, septicaemia most commonly occurs secondary to leg abrasions or pneumonia. Septicaemia itself may cause diffuse pneumonia or embolic pneumonia.

Septicaemia is more often a histological diagnosis. On post mortem there may be multiple small haemorrhages on the heart or internal surface of the rib cage. Be sure to check for predisposing conditions including endocarditis, cellulitis, or pneumonia.

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