Effects of training on resting peripheral blood and BAL-derived leucocyte function in horses

In this study, the effects of prolonged, high intensity training on aspects of peripheral blood and bronchoalveolar lavage (BAL)-derived leucocyte fun ction were evaluated in 8 horses. All horses undertook a 7 week endurance t raining programme, followed by 5 weeks of high intensity training CHIT). Th ereafter, horses were divided into control (C) and overtraining (OT) groups . The frequency and intensity of training were increased more substantially for horses in the OT group. Training nas terminated in week 32 when horses in the OT group demonstrated a significant performance reduction. Peripher al blood and BAL samples were collected from 4 horses in C and OT groups in training weeks 7, 11, 14, 18, 22, 28 and 32. Flow cytometric techniques we re used to assess phagocytosis by peripheral blood neutrophils and pulmonar y alveolar macrophages (PAM)), and oxidative burst activity of neutrophils, PAM, peripheral blood and BAL-derived lymphocytes. Peripheral blood neutro phil phagocytosis (internalisation) increased during the initial HIT period and decreased from week 16 when the training workload was increased for bo th groups. The oxidative burst activity of peripheral blood neutrophils and lymphocytes similarly increased and then decreased in response to training . The oxidative burst activity of PAM was reduced towards the end of the ov ertraining phase of the programme. Pulmonary alveolar macrophage phagocytos is and oxidative burst activity of BAL-derived lymphocytes demonstrated no change throughout the course of the study. There was no difference in resul ts obtained from C or OT group horses, suggesting that protracted HIT, rath er than overtraining, was associated with impaired cell function. The detrimental effects observed in peripheral blood neitrophil and PAM fun ction may indicate impaired nonspecific immunity which may adversely affect the health and performance of horses undergoing protracted periods of inte nse training.