ACVIM 2026 | Education

Can physiologic stress budge SAA levels?

By Paul Basilio

Serum amyloid A (SAA) has a lot going for it as a biomarker. In a healthy horse, levels of the acute-phase protein are typically quite low, but those levels can rapidly increase—up to 1,000-fold in some cases—in response to inflammatory or infectious stimuli. In addition, no major breed or sex differences are observed in either the normal or abnormal concentrations.

While it’s a nonspecific marker of inflammation that shouldn’t be used for etiologic diagnoses, its response to elective surgical procedures, vaccination, transportation and even exercise suggests that some physiologic stimuli can influence the SAA concentration.

This physiologic component led Diana Perez-Solano, DVM, a large animal internal medicine resident at the University of Wisconsin, and her colleagues to wonder whether the stress alone could also influence the SAA concentrations.

Stress activates narrow endocrine pathways, including the hypothalamic-pituitary-adrenal axis, which results in measurable changes in cortisol, adrenocorticotropic hormone (ACTH) and blood glucose concentrations.

“Interestingly, some stressful events have been associated with an increase in SAA concentrations in calves, but this relationship has not been well characterized in horses,” Dr. Perez-Solano said.

The study
The team designed a prospective observational cohort study to evaluate the effect of routine medical procedures on SAA concentrations in healthy adult mares. The secondary objective was to develop and assess a modified behavioral stress scoring system to evaluate equine stress associated with teaching procedures.

Nine healthy adult mares between 11 and 26 years of age were enrolled and underwent teaching labs conducted by fourth-year veterinary students under faculty supervision.

“The specific teaching labs included colic workup, which was expected to be a major stress procedure consisting of a rectal palpation, nasogastric intubation and abdominocentesis,” Dr. Perez-Solano said. “A reproductive evaluation, which was expected to be a minor stress procedure, included rectal palpation and a transrectal ultrasound. Depending on the findings of that transrectal ultrasound, some mares also received uterine lavage.”

Seven mares underwent the colic workup, and 8 received the reproduction evaluation.

Blood was collected before the teaching lab and at 30 minutes and 1 day afterward. A novel modified stress-scoring system (MSS) based on behavioral cues was used before, during and after the procedures. For the study, stress was defined as an increase from baseline in blood glucose, cortisol and ACTH at 30 minutes postprocedure. Some mares received sedation as necessary to maintain safety, she explained.

SAA was measured using a point-of-care assay (Stablelab; Zoetis Equine) and a latex agglutination test (VET-SAA; Eiken)

“There was a significant increase in ACTH, cortisol and glucose concentrations after the labs,” Dr. Perez-Solano said, adding that the MSS scores also increased after the procedures when compared with baseline.

“That means that the teaching procedure induced measurable physiologic and behavioral stress responses,” she explained.

Those stress responses did not translate into increased SAA levels, however. “There were no significant changes in any of the time points for SAA in either of the assays that we used,” Dr. Perez Solano said.

While the team’s initial hypothesis that stressful procedures would elicit an SAA response did not hold up, the results reinforce SAA’s reliability as a biomarker for inflammation, she said.

“In addition, our modified stress score showed promise as a useful indicator of equine stress during teaching procedures, but validation for repeatability in a large group of horses is required.” MeV