The effect of introduction to training on some haematological and immunological parameters in the thoroughbred horse

Good health of the racing horse is essential to optimal training and, thus, high levels of performance. However, epidemiological research has shown that respiratory disease, especially in young horses, is an important contributor to wastage in the industry, and, as such causes a significant economic loss to the thoroughbred industry. Both, acute and chronic exercise, have been associated with changes in immunological, haematological and biochemical parameters. A connection between exercise, disease and in vitro measurements has been suggested by research studies published to date. Mechanisms underlying these changes are complex and multifactorial, but have been linked to changes in the endocrine system as a response to the stress imposed on the body by exercise. The present study sought to investigate the effects of introduction to training on some immunological parameters in the thoroughbred horse. Blood samples from 20 thoroughbreds in National Hunt training in two local yards were taken prior to and after two, eight and ten weeks of training. Lymphoproliferative response against stimulation with Concanavalin A was examined by a nonradioactive assay immediately upon collection of the blood samples. The functioning of the innate immune system was evaluated by establishing phagocytosis and oxidative burst capacity of granulocytes and monocytes. Results showed that oxidative burst capacity of granulocytes and monocytes significantly increased during training (Yard One: p<0.05; Yard Two: p<0.001). Granulocyte and monocyte phagocytosis fluctuated during training (p<0.01). Changes were associated with other external factors such as training intensity and duration. Lymphocyte proliferation was not significantly affected by chronic exercise training (p>0.05). A second aim of this study was to assess the effect of introduction to training on some plasma haematological and biochemical parameters. Analysis of blood samples was undertaken by the Irish Equine Centre. Both, plasma haematology and biochemistry remained largely uninfluenced by chronic exercise training (p>0.05). However, significant changes that resembled a ‘stress leukogramm’ in neutrophil and lymphocyte percentage were observed in one yard during training (p<0.001) which may indicate that factors such as training intensity moderate the effect of exercise on leukocytes. Elevated levels of GGT, total bilirubin and globulins were observed in horses during the training period examined. A trend towards decreasing levels of eosinophils, total bilirubin, total protein, albumin and globulins was observed in this study (p<0.05). Also, a trend towards increasing levels of total erythrocytes, PCV and monocytes was detected in the present study, however, changes were non-significant (p>0.05) except in the case of haemoglobin (p<0.05). In summary, several components of the immune system appeared to change with training. However, components of the innate system seemed to be more susceptible to change than components of the adaptive immune system. Although the clinical consequences of these training-induced alterations of the immune response are not yet known, managers of horses should take into account that the immune system of a horse may be affected by chronic exercise training. This appears particularly important considering the importance of wastage in racehorses caused by infectious disease.