Serum amyloid A (SAA) is an acute-phase protein, meaning its levels in the blood increase rapidly in response to infection, injury, or stress. Due to its rapid increase during inflammatory conditions, SAA is often used in horses as a biomarker to assess inflammation or infection
Researchers at the Department of Clinical Sciences, College of Veterinary Medicine, Kansas State University, conducted a two-part study to monitor the response to vaccination. Cassandra M. Baumgarten was the lead author of the study, which was published in the Journal of the American Veterinary Medical Association.
The study included a total of 36 clinically normal horses. Twenty-eight horses received routine booster vaccinations recommended for horses in the southern states of the USA (rabies, tetanus, West Nile virus, Eastern and Western equine encephalomyelitis, equine herpesvirus-1/-4, and influenza). Eight horses received placebo injections of saline.
The research team conducted daily clinical examinations of the horses, which included measuring their temperature and collecting blood samples to monitor serum amyloid A (SAA) levels for the first ten days after vaccination.
They found that, compared to the control group, vaccinated horses had higher SAA concentrations for up to ten days after vaccination, generally returning to normal by the ninth day. About 85.7% of the horses had their SAA levels return to normal within ten days of vaccination.
Fever (temperature >38.4°C) was observed in 78.6% of the horses after vaccination, but there was no correlation between fever and SAA concentration.
The authors suggest that elevated SAA levels for 10 days after vaccination and fever lasting 12 to 24 hours cannot be used as indicators of illness. They recommend that clinicians, when assessing a patient’s condition after vaccination, should not rely on just one or two clinical signs but rather evaluate the patient as a whole. They also state that measuring SAA for 10 days post-vaccination cannot reliably indicate illness.
Based on their findings that routine vaccination increases SAA concentrations, the authors suggest that when advising horse owners about travel or competition, practitioners should recommend a recovery period following vaccination.
They also suggest the need for further studies to investigate the effect of travel or competition on the antibody response.
For more details, see:
Baumgarten, C. M., Delph Miller, K. M., Davis, E. G., Beard, L. A., Blevins, C. A., Wottowa, M., Hill, M., & Larson, R. L. (2024).
Serum amyloid A increases following routine vaccination of healthy adult horses.
Journal of the American Veterinary Medical Association, 262(9), 1181-1187.
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