South African Equine Veterinary Association Congress 2015 Protea Hotel Stellenbosch
Samples should be submitted for worm egg count, wet smear examination for cyathostomin
larvae, occult blood and potentially bacteriology/clostridial toxin analysis. Be aware that horses
with chronic diarrhoea are more likely to shed Salmonella spp and give a positive culture/PCR.
Routine haematology: common findings associated with chronic diarrhoea
Anaemia of chronic disease is a common finding in horses with chronic diarrhoea. Chronic
disease will result in a packed cell volume (PCV) in the range of 20-30%. The anaemia occurs
due to a combination of reduced red cell lifespan, reduced marrow responsiveness (as a result of
either decreased erythropoietin or reduced response to erythropoietin), and reduced free iron.
Anaemia due to chronic disease will occur within approximately 10 days of the start of the disease
process. Lower PCVs (<20%) will usually be due to haemolytic or haemorrhagic disorders.
White cell parameters may be normal or show changes consistent with chronic inflammation.
Mature neutrophilia can occur with excitement, physiologic stress or administration of
corticosteroids and is often indicative of a non-specific inflammatory response. High counts, in
conjunction with elevated fibrinogen and globulins, are more suggestive of an infectious process
and are also a common finding in larval cyathostominosis. Monocytosis is an indication of a
chronic inflammatory process. Eosinophilia is uncommon but may rarely be associated w ith a
significant parasite burden or systemic disease process such as multisystemic eosinophilic
epitheliotrophic disease (MEED).
Leukaemia is rarely seen with lymphoma, but very occasionally a marked lymphocytosis with
abnormal cells can occur.
Acute phase proteins (APP) should be assessed. Serum amyloid A (SAA) is a positive major APP
and has low concentrations in the plasma of healthy horses. Concentrations of SAA increase
rapidly, often to greater than 100-fold, during the acute phase response and there is a rapid
decrease in concentration with disease resolution. Normal SAA values in healthy horses range
from 0-20mg/l and increase within 12 hours of tissue injury, to peak at 24-48 hours.
Fibrinogen is relatively insensitive as it takes several days to increase after the induction of
inflammation and 3-6 days to reach a peak response. Use in conjunction with SAA can help to
monitor progression of the disease process and response to treatment.
Protein electrophoresis identifies elevations in specific globulin fractions.
- Alpha 2 globulins include the acute phase proteins
- Beta 1 globulins are associated with large strongyle and larval cyathostomin activity
- Beta 2 globulins are associated with hepatopathy
- Elevation in gamma globulins occurs in response to bacterial or viral infections
Some neoplasms, such as lymphosarcoma, can result in a monoclonal gammopathy (usually seen
as a significant elevation in beta or gamma globulins) due to uncontrolled production of a single
immunoglobulin. In practice, protein electrophoresis is rarely helpful in providing a diagnosis for
chronic diarrhoea.
Routine biochemistry: common findings associated with chronic diarrhoea
Total protein can vary associated with hydration status, depending on the severity of the
diarrhoea, and any underlying inflammatory processes. The protein should be evaluated in
conjunction with the hydration status of the horse. Albumin is a very useful parameter to monitor;
marked hypoalbuminaemia (<20g/l) indicates significant protein loss and intestinal pathology.
Non-specific chronic diarrhoea cases can have normal albumin values or only mild
hypoalbuminaemia. Globulins may be elevated with chronic inflammation, parasites and
neoplasia. Hypoglobulinaemia may occur with significant intestinal pathology and protein loss.
Gamma glutamyl transferase (GGT) can be elevated in some cases with enteropathy, in the
absence of liver disease. Other liver enzymes (GLDH, AST, ALP) and bile acids should be
compared to rule out concurrent liver disease.
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