Properties of herbage in relation to equine dysautonomia: Biochemical composition and antioxidant and prooxidant actions

To investigate the etiology of equine dysautonomia (ED), a degenerative pol yneuropathy affecting grazing horses, the biochemical composition and antio xidant/prooxjdant activities of aqueous extracts of plants collected from E D pastures were determined. Plants collected immediately after an outbreak of ED had reduced antioxidant and weak prooxidant activities when compared with control plants (plants collected from ED pastures out of ED season and control plants from ED pastures that were grown under favorable conditions ). ED plants also had significantly increased concentrations of fructose an d low molecular weight phenolic compounds, significantly more of one amino acid zone (probably valine), significantly less tartaric acid, and a nonsig nificant decrease in ascorbic acid content when compared with control plant s from ED pastures that were grown under favorable conditions. These findin gs suggest that ED plants may be under oxidative stress, possibly due to ch illing, drought, or fungal colonization. However, experimental drought and chilling of plants did not reproduce the biochemical alterations identified in ED plants. It is possible that the altered biochemical content of inges ted plants may contribute, directly or indirectly, to the development of ED in grazing horses.