From stable to stable: how does stress influence the first line of immune defense in sport horses

Abstract

Stressful factors, including physical exercise, can influence the body’s defense mechanisms and can be involved in the etiology and evolution of systemic diseases. The aim of this study was to investigate the influence of various stressors to which sport horses are commonly subjected on the innate immune system. For this, four experimental protocols were designed including different animals, namely: (a) resting horses subjected to everyday medium level exercise (n = 18, average age = 7 years, range: 6 to 11 years), (b) medium course transportation, where the distance of one-way trips represented 270 km (n = 8, average age = 7 years, range: 6 to 9 years), (c) a long course, with a 561 km one-way distance (n = 5, average age = 8.2, range: 7 to 11 years) and (d) pre- and post-competition investigations (n = 9, average age = 7 years, range: 6 to 11). Blood was sampled on heparine (50 UI/ml) before and after the workout or transportation. The phagocytic activity of leukocytes was measured by a carbon particle inclusion test, along with total immunoglobulin/opsonin levels (Ig) (24% Zn sulphate precipitation test) and circulating immune complexes (4.2% polyethylene glycol precipitation test). The results were statistically interpreted by use of Micrososft Excel program (Student’s t test). The various types of stress differently influenced the equine athletes. While a moderate daily exercise did not substantially influence the humoral and cellular effectors of innate immunity, transportation exerted stronger beneficial effects based on the distance to the competition site. As a fast acting antimicrobial mechanism, the phagocytosis underwent the most pronounced changes, positively influenced mainly by the short course transportation. While the transportation stress enhanced phagocytosis, the competition decreased the potential of the cells to react, without significantly influencing their numbers. The experiment suggested that management measures, such as age-tailored exercise and maternal care and diet could help in alleviating stress from stable to stable, during the competition season, thus improving animal welfare and allowing a better health forecast.