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7.7 How to interpret gross changes found at necropsy
Small lesions can be recent or slow growing; Large lesions mean long standing or fast
growth.
Non uniformity of size of multiple lesions means ongoing event or waves. Uniformity indicates recent lesions or single event.
Coalescing lesions indicate long standing and continued growth. Miliary lesions indicate showering.
Patterns, segmental and symmetrical lesions are often outlines of vascular bed or
units of tissue architecture.
Raised lesions are due to injection of fluid, cells or stroma. Depressed lesions are necrosis, atrophy or fibrosis.
Flat lesions are congenital or recent. Amorphous texture and consistency of lesions are pus, exudate or necrosis.
Solid texture and consistency of lesions are usually live tissues except for tubercles
and calcified granulomas.
Hardness and grittiness are bone, cartilage or calcification. Firmness occurs in stroma-rich, fluid-poor tissues.
Softness occurs in stroma-poor, fluid-rich tissues. Gas is from lungs, aspirating wounds or bacterial production.
Dark tissues have high pigment to tissue ratio i.e. muscle, spleen, liver. Light coloured tissues have a high fat to tissue ratio i.e. brain or a low pigment to
tissue ratio i.e. scar tissue or lung.
Pigments are haemoglobin, myoglobin, bile and sometimes bacterial products such as
H
2
S or fungal fruiting bodies.
Green is usually bile, green-black is bile or bacterial H
2
S and are limited to serosal or capsular surfaces.
Black tissue is from melanin. Black faeces melaena are from digested blood. Blue black can be intense haemorrhage.
White to grey to yellow is lack of blood or accumulation of leucocytes. Red to reddish black is blood or haemorrhage. Congestion is diffuse widespread and
poorly demarcated.
Necrosis is pale and associated white-yellow exudates will cause raised surfaces.
Blood can darken exudates.
7.8 Common diagnostic mistakes at necropsy
Rumenitis
– Sloughing of the rumen mucosa is a normal postmortem change and is not evidence of rumenitis or excessive grain feeding.
Pneumonia
– Discoloration of the lungs on its own is not a sign of pneumonia. Pneumonia should be diagnosed by feel. Normal lungs are soft and spongy even if discoloured by
pooling of blood or congestion. Lungs with pneumonia feel consolidated like liver.
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Enteritis
– red to blue-black intestines containing bloody fluid is often a postmortem artifact and should not be diagnosed as haemorrhagic enteritis unless accompanied by necrosis,
oedema, ulceration or fibrin.
Blood poisoning
– petechial or ecchymotic haemorrhages affecting the heart are a normal post mortem finding in cattle particularly in cattle that have been euthanased. Haemorrhages
elsewhere in the body are more likely to be associated with septicaemia or a clotting defect.
Hyperthermia
– core body temperature normally elevates considerably after death in large, fat, hairy or otherwise well insulated cattle. However it usually takes a few hours before the
temperatures approach the levels expected in heat stroke ≥43C.
Bloat
– well conditioned animals can bloat quickly after death and develop signs resembling true bloat such as congestion of the head and neck and an oesophageal bloat line if post
mortem bloating occurs before blood coagulates.
Enterotoxaemiapulpy kidney
– Enterotoxaemia aka pulpy kidney is unlikely to occur in export cattle. Pale mushy, pulpy kidneys are a normal post mortem change more
pronounced in hot conditions. Enterotoxaemia is difficult to diagnose in cattle but if suspected the brain should be sampled for histology and urine tested for presence of
glucose.
7.9 Veterinary necropsy equipment checklist
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