title: Prolonged suppression of the innate immune system in the horse following an 80 km endurance race.
abstract: BACKGROUND
  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.
  
  
  OBJECTIVE
  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.
  
  
  CONCLUSIONS
  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.
authors.affiliation: Physiological Sciences, University of Stellenbosch, Private Bag X1, 7602 Matieland, South Africa.
authors.forename: P J
authors.initials: PJ
authors.lastname: Robson
authors.forename: T D
authors.initials: TD
authors.lastname: Alston
authors.forename: K H
authors.initials: KH
authors.lastname: Myburgh
mesh_terms: D000818:Animals; D001786:Blood Glucose / Q000032:analysis; D005973:Glutamine / Q000097:blood; D006736:Horses / Q000097:blood / Q000276:immunology* / Q000502:physiology; D006854:Hydrocortisone / Q000097:blood; D007113:Immunity, Innate / Q000276:immunology / Q000502:physiology*; D007958:Leukocyte Count / Q000662:veterinary; D009000:Monocytes / Q000166:cytology / Q000276:immunology / Q000378:metabolism; D009504:Neutrophils / Q000166:cytology / Q000276:immunology / Q000378:metabolism; D010805:Physical Conditioning, Animal / Q000502:physiology*; D010807:Physical Endurance / Q000276:immunology / Q000502:physiology; D016897:Respiratory Burst
chemical_list: D001786:Blood Glucose; D005973:Glutamine; D006854:Hydrocortisone