Summary: Reasons for performing study: Changes in serum levels of acute phase proteins (APPs) reflect the acute phase reaction, a rapid and nonspecific response to any tissue damage. Serum amyloid A (SAA) is the main APP in horses, which increases in various diseases, surgical injuries and after long distance endurance rides; however, this nonspecific parameter has not been investigated as an indicator of subclinical disorders, which may result in elimination during endurance competitions. Objectives: To evaluate the serum concentration of SAA as a potential indicator for the status of horses prepared for long distance endurance rides (120 and 160 km). Materials and methods: Twenty Arabian horses were tested and 12 were eliminated during the ride and 8 completed the distances. Routine haematological and biochemical tests and measurement of serum concentrations of SAA were carried out before and after the competition. Results were compared using the Mann Whitney U test. Results: Before the competition all haematological and biochemical parameters varied within reference ranges with no differences between the eliminated horses and the ones that successfully finished the competition. After the rides creatine phosphokinase activity and neutrophil: lymphocyte ratio reflecting exercise‐induced leukogram changes increased (P<0.05) in both groups. Before the competition, the concentration of SAA remained within reference ranges; however, it was significantly (P<0.05) lower in horses that successfully finished the competition than in eliminated ones (411.7 ± 144 ng/ml vs. 5809.5 ± 2242.7 ng/ml). After the ride SAA levels increased (P<0.05) and were similar in both groups (13 833.8 ± 1354.3 ng/ml and 12 831.2 ± 1317.6 ng/ml). Conclusions: Serum SAA level was the only laboratory parameter that indicated most (66.6%) of the eliminated horses before entering the competition. None of the horses with SAA level higher than 1000 ng/ml completed the distance. Thus, it may be postulated that serum SAA concentration may indicate a poor status of a horse, resulting in elimination during a competition.

Serum amyloid A (SAA) is the major acute phase protein in horses. Its concentration increases in various pathologies but also in response to prolonged, strenuous effort. The purpose of this study was to establish whether routine race and endurance training produces changes in the SAA level in Arabian horses. Additionally, the differences between SAA response in experienced endurance horses and endurance horses that were beginning their career were investigated.