Prolonged suppression of the innate immune system in the horse following an 80 km endurance race

Abstract

Summary Reasons for performing study: An increased susceptibility to bacterial and viral infections of the respiratory tract, which results in a loss of performance, has been reported in racehorses. Much research has focused on the influence of high‐intensity exercise of a short duration on immune system function in horses, but scant attention has been given to prolonged endurance exercise as an immune modulator. Objectives: The objective of this study was to evaluate the effect of an 80 km endurance race on the monocyte and neutrophil oxidative burst, serum Cortisol, glutamine and plasma glucose concentrations in 8 endurance‐trained horses (mean ± s.d. age 9.4 ± 2.2 years). Methods: Blood samples were drawn from the horses prior to and following an 80 km ride. Results: Mean time for completion of the 80 km race was 306 ± 40 mins. Immediately post race mean serum Cortisol concentration, blood monocyte and neutrophil counts were higher and blood lymphocyte counts and plasma glucose concentration were lower compared with prerace values (P<0.05). Neutrophil and monocyte oxidative burst activity decreased following the race and had not regained prerace values after 3 days of rest (P<0.05). Conclusions: The present study indicates that long duration exercise in horses has a negative impact on the function of the innate immune system that lasts several days post race. Precise mechanisms instigating the fall in innate immune system function are unclear and multifactorial, but may be attributed, at least in part, to a high serum Cortisol response during very prolonged exercise. Potential clinical relevance: A prolonged bout of exercise results in a long‐term suppression of the innate immune system function in horses which may, in part, account for the observed increase of infectious episodes in horses during training.

Perfil hematológico de equinos submetidos à prova de Team Penning

“…Porém, neste estudo, observou-se que o valor de RDW permaneceu inalterado depois da atividade física exercida pelos animais e sem diferenças entre os Grupos A, B, C e D. Provavelmente, a liberação de células pelo baço foi mínima e insuficiente para provocar grande heterogeneidade entre as hemácias. Leucocitose com neutrofilia foi detectada em eqüinos após exercício por Robson et al (2003). Para Krumrych (2006), a atividade física é considerada um fator estressante que induz leucocitose.…”

“…Depois do aumento transitório do número de linfócitos existe outro aumento de leucócito relacionado com uma pequena linfopenia e uma forte neutrofilia, resultante da liberação de um pool de granulócitos e aumento da liberação destas células pela medula óssea (Persson 1983). Acredita-se que a mudança na cinética leucocitária, manifestada pelo aumento da rela- ção neutrófilo/linfócito, está relacionada com o aumento da concentração de hormônio adrenocortical, principalmente, cortisol no sangue (Jensen-Waern et al 1999, Robson et al 2003. Este hormônio não estimula somente a produção de neutrófilo pela medula óssea e sua liberação para o sangue periférico, mas também inibe a migração destas células para o espaço intravascular (Pyne 1994) e interfere no número de linfócitos circulantes (Shinkai et al 1996).…”

Experimental immunology Lymphocyte proliferation activity after limited (Light class) and long (CEI) distance endurance rides in horses

“…This condition is believed to result from alterations in the number and functions of circulating leukocytes. Several reports confirmed the diminished neutrophil function during this period in human and equine athletes [2,5,7,8]. However, variable results on the lymphocyte response after exercise have been presented, suggesting that it is highly heterogeneous [8][9][10].…”

“…In our study exercise-induced changes in leukocyte numbers manifested as neutrophilic leukocytosis resulting in an increase in N : L ration after both: limited distance (Light class) and long distance (CEI) rides. This kind of changes is known as stress leukogram and has been widely reported after intensive or prolonged exertion [5,7,16,20,22]. In endurance exercise, the changes result from biphasic, catecholamine and cortisol dependent process [7,22].…”

“…Many evidence suggest, that strenuous, high-intensity or long lasting exercise may promote immunosuppression which can lead to increase susceptibility to disease in human and equine athletes [1][2][3][4][5][6][7]. This condition is believed to result from alterations in the number and functions of circulating leukocytes.…”