The Use of Serum Amyloid A (SAA) to Detect Early Inflammation

"SAA is a more reliable indicator for early inflammation compared with abnormal physical parameters such as fever,” noted researchers in this study.

Transport stress is a known risk factor for the development of respiratory disease following long-distance travel. It is generally advised to check a horse’s rectal temperature twice daily along with a clinical impression based on a physical exam. A study looked at the potential usefulness of using a biomarker such as serum amyloid A (SAA) to identify inflammatory events as early as possible and compared that to monitoring for an elevated rectal temperature [Oertly, M.; Gerber, V.; Anhold, H.; et al. The Accuracy of Serum Amyloid A in Determining Early Inflammation in Horses After Long-Distance Transportation by Air. Journal of Equine Veterinary Science 2021, vol. 97; doi.org/10.1016/j.jevs.2020.103337].

A rapid increase of SAA over 6-12 hours makes it more useful that using fibrinogen that takes 72 hours to increase. A shorter half-life of SAA is also helped to identify response to treatment.

In this study, 122 Warmblood horses flew from Europe to Miami for a five-star show jumping competition. Before the flight and upon arrival, the horses were given a veterinary assessment of attitude, rectal temperature, heart and respiratory rates, mucous membranes, breathing pattern, cough reflex, nasal discharge, lung auscultation, and submandibular lymph node palpation. Rectal temperature was taken twice daily, and SAA measurement of whole blood once daily, which was checked again 24 hours after arrival. If a horse developed a fever and/or had an elevated SAA >25 ug/ml, SAA was rechecked very 24 hours until it dropped to <15 ug/ml and the horse appeared clinically healthy. After 10 days at the venue, the horses were then flown to Mexico City from Miami with a repeat of the same assessments.

Previous studies have shown that fever is highest between 20-49 hours after the start of transport. Clinical signs of shipping fever were observed in 47.2% of horses—about 19% had fever, yet 28% did not—indicating that fever is not a conclusive guarantee to identify illness. In contrast, nearly 67% of horses with an SAA level >23 ug/ml upon arrival showed signs (coughing) of shipping fever by 24 hours. For those horses, resolution of clinical signs correlated with a decrease of SAA levels by 50% every 24 hours.

Conclusion

Based on the study findings, the authors confirmed that “SAA is a more reliable indicator for early inflammation compared with abnormal physical parameters such as fever.” An SAA ≥23 ug/ml as measured 24 hours following transport is associated with a sensitivity of 93.3% and specificity of 91.3% to differentiate sick from healthy horses.

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