Serum amyloid A (SAA) as an aid in the management of infectious disease in the foal: comparison with total leucocyte count, neutrophil count and fibrinogen.
Authors: Hultén C, Demmers S
Journal: Equine veterinary journal
Summary
# Editorial Summary When neonatal foals present with signs of possible infection, veterinarians face a critical diagnostic challenge: distinguishing genuine bacterial disease from self-limiting or non-infectious conditions, since delayed treatment of sepsis is life-threatening but unnecessary antibiotics carry significant cost and welfare implications. Hultén and Demmers compared serum amyloid A (SAA)—an acute phase protein—with conventional inflammatory markers (fibrinogen, total white blood cell count, and neutrophil numbers) across 25 hospitalised foals presenting with neonatal weakness, pneumonia, or diarrhoea, sampling on admission and serially throughout hospitalisation. On presentation, foals with confirmed bacterial infections showed markedly elevated SAA and fibrinogen concentrations; critically, foals with negative blood cultures displayed normal SAA despite variable leucocyte responses, while those with positive blood cultures developed leucopenia alongside extremely high SAA—suggesting SAA is more discriminatory for true sepsis than traditional markers. Most significantly, SAA normalised rapidly on discharge in recovered foals, whereas fibrinogen and white cell counts remained elevated, indicating that SAA may provide earlier reassurance of treatment response in conditions such as *Rhodococcus equi* pneumonia and potentially guide the timing of antimicrobial withdrawal. In clinical practice, incorporating SAA measurement could strengthen diagnostic confidence in ambiguous neonatal cases, reduce unnecessary prolonged antibiotic exposure in non-bacterial disease, and offer a more sensitive treatment endpoint than relying solely on haematological parameters.
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Practical Takeaways
- •SAA can aid in differentiating bacterial from non-bacterial infections in neonatal foals, particularly those presenting with weakness—normal SAA suggests non-bacterial disease and better prognosis
- •SAA normalizes faster than traditional markers (fibrinogen, WBC count) during recovery from Rhodococcus equi pneumonia, making it useful for monitoring treatment response and discharge planning
- •SAA is not reliably useful for evaluating foals with diarrhoea as the primary sign, regardless of rotavirus status, so should be combined with other diagnostic approaches for this condition
Key Findings
- •SAA and fibrinogen concentrations on admission were significantly higher in foals with bacterial infections (n=8) compared to non-bacterial or uncertain diagnoses (n=17)
- •Foals with positive blood cultures showed markedly increased SAA and leuco-/neutropenia, while those with negative blood cultures had normal SAA and fibrinogen concentrations
- •SAA normalized more rapidly than fibrinogen and white blood cell counts on discharge in recovered foals with Rhodococcus equi pneumonia
- •SAA measurements showed no consistent inflammatory pattern in diarrhoeic foals, with no statistical difference between rotavirus-positive and rotavirus-negative cases