EN
Long-distance endurance rides involve strenuous effort, which induces numerous changes in the horse’s body, including the exercise-induced acute-phase response (APR). Such a reaction has also been reported in humans and dogs after exertion, but it varies depending on the species and the type of exercise. In horses, the exerciseinduced APR is manifested as an increase in serum amyloid A (SAA) after the effort, but the mechanism and regulation of this process has not been clearly understood. The aim of this study was therefore to determine the changes in the concentration of cytokines that are believed to regulate this type of reaction. Twelve horses competing in 120 km and 160 km endurance rides were included in the study. The routine haematological and biochemical blood test, as well as the measurements of SAA, IL-1, IL-4, IL-6, IL-10, and TNFα, were carried out before and after competitions. Typical haematological changes and increases in SAA levels were accompanied by increases in IL-6 and IL-10 concentrations, which were also positively correlated before the effort. Taking into account the sampling time, it is postulated that the exercise-induced APR is promoted by type 1 cytokines. It has also been concluded that the exercise-induced APR in horses in regular training is accompanied by strong a anti-inflammatory response, which prevents clinical disorders after long-distance rides. Then, the overall “anti-inflammatory state” defined previously in race horses is also likely to occur in endurance horses.