Oxidative stress, respiratory health and equine transport

Transportation of horses is a matter of welfare concern. It may predispose animals to shipping fever (i.e. transport pneumonia) and induce oxidative stress (OS); however, the role of OS in the pathogenesis of shipping fever has yet to be explored. The aim of this study was to evaluate markers of OS and other systemic and local respiratory indicators of inflammation on horses undergoing an 8 hour road transportation event. Twelve horses were examined prior to transportation (T1), at unloading (T2), one (T3) and five days (T4) post transportation. At each time point, blood samples were collected to evaluate leucogram and OS biomarkers (derivatives of reactive oxygen metabolites
(d-ROMs) and total plasma antioxidant status (PTAS)). The respiratory tract was examined by endoscopy and tracheal washes (TW) were collected for differential cell count and bacteriological evaluation. Transportation resulted in an increase in the proportion of neutrophils in blood and TW, tracheal mucus and TW bacterial concentration with evidence of reduced bacterial diversity due to an increase in Pasteurellacea. Tracheal bacterial concentration (cfu/
ml) was highest at unloading (Pindicated by elevated d-ROMs concentration and oxidative stress index values (P=0.05 and P=0.02, respectively) compared to horses that did not present TW neutrophilia at T4. Furthermore, PTAS decreased only in horses that presented persistent TW neutrophilia post transport (T4 vs T1; P= 0.02). Transportation induces respiratory system inflammation resulting in horses being exposed to OS. As proposed for other species, monitoring OS could be a useful tool to assess stress and disease-susceptibility, and consequently the welfare of transported horses.