Background: Inflammatory airway disease (IAD) is prevalent in young racehorses during training, being the 2nd most commonly diagnosed ailment interrupting training of 2-year-old Thoroughbred racehorses.
Hypothesis: That stabling and exercise cause oxidative stress, release of platelet-activating factor (PAF) and inflammation in airways of Thoroughbred colts.
Animals: Colts in breeding farms (NC, n = 45), stabled for 30 days (EC, n = 40), and race trained (EX, n = 34).
Methods: Cytological profile and parameters of bronchoalveolar lavage fluid (BALF) related to oxidative stress, bioactivity of the proinflammatory mediator PAF, catalase activity, and alveolar macrophage function.
Results: Percentages of neutrophils and eosinophils in the BALF of the EX group were higher (5.4 +/- 6.4% versus 0.9 +/- 1.2%) than the upper limits for normal horses (3-5%). BALF from the EX group (45.6 +/- 2.8 cells/microL of BALF) also displayed significantly (P = .017) higher total nucleated cell count. PAF bioactivity and the total protein concentration in the BALF were higher in the EX group (0.0683 +/- 0.076 versus 0.0056 +/- 0.007 340 : 380 nm ratio P = .0039, 0.36 +/- 0.30 versus 0.14 +/- 0.15 mg of proteins/mL of BALF P < .001). Concentration of BALF hydroperoxides was higher in the EC group (104.7 +/- 80.0 versus 35.2 +/- 28.0 nmol/mg of proteins, P = .013) and catalase activity was higher in the EX group (0.24 +/- 0.16 versus 0.06 +/- 0.02 micromol H2O2/min/mg of proteins, P = .0021). Alveolar macrophage phagocytosis (P = .048) as well as production of superoxide anion (P = .0014) and hydrogen peroxide (P = .0011) were significantly lower in EX group.
Conclusions and clinical importance: Further studies should be performed to elucidate the role of PAF in the pathophysiology of IAD. Its presence in bronchoalveolar fluid of young athletic horses makes it a potential therapeutic target to be investigated.