Effects of Transportation on Redox Homeostasis and Tracheal Mucus

The aim of this pilot study was to document the effects of transportation on markers of oxidative stress (OS) in blood, exhaled breath condensate (EBC), and saliva and to explore their relationships with transport-related increases in tracheal mucus. Twelve horses, six Standardbred, and six Thoroughbred, aging from 3 to 8 years, underwent an 8-hour journey during which they had no access to food or water. Clinical examinations and sampling of blood, EBC, and saliva were performed preloading, at unloading, 12 and 24 hours, and 5 days after journey. Concentration of oxidants (reactive oxygen metabolites [ROMs], advanced oxidation protein product [AOPP], ceruloplasmin [CP], hydrogen peroxide in the EBC) and antioxidants (plasma total antioxidant status [PTAS] and saliva total antioxidant status [STAS], glutathione) were determined, and the oxidative stress index (OSI = ROMs/PTAS × 100) was calculated. Respiratory endoscopy was performed at preloading and unloading, and tracheal mucus was scored. Oxidative stress variables were analyzed using proc mixed procedure with time as the fixed factor, and the variation in mucus score was analyzed by median test. The relationships between OS markers and mucus score were examined by linear regression analysis. Transportation caused a significant increase in tracheal mucus and in the concentrations of ROMs, AOPP, CP, PTAS, and STAS (all P > .05). Tracheal mucus was positively associated with ROMs and OSI (R2 = 57.8, P = .004; and R2 = 70.3, P < .001, respectively). However, animals did not experience OS, as reflected in the lack of changes in OSI. Overall, although the transported horses experienced oxidative and respiratory challenges, they were able to maintain redox homeostasis and did not develop clinical disease.