HISTOPATHOLOGY OF THE BRAIN-STEM NUCLEI OF HORSES WITH MAL SECO, AN EQUINE DYSAUTONOMIA

''Mal seco'' is a disease of unknown aetiology affecting horses in Arg entina. It is similar to grass sickness, a primary dysautonomia of hor ses in Europe. A histopathological study of the brain stem nuclei of t hree horses with ''mal seco'' was performed. Changes were found that c onsisted of chromatolysis, cytoplasmic vacoules, eosinophilic sphaeroi ds, and pyknotic and eccentric nuclei. These changes were most severe at the oculomotor, vestibular and abducent nuclei. The results provide further evidence to suggest that ''mal seco'' and grass sickness may be the same disease.