Clinical signs and diagnosis of acute grass sickness in horses in Switzerland and in Southern Germany

Six hones with acute grass sickness presented to the Clinic for Ruminant an d Equine Medicine, University of Zurich between May 1996 and May 1998 were included into the present study (case series). Clinical symptoms, laborator y results and the results of necropsy, histologic examinations and immunhis tochemical examinations were reviewed and analysed. All horses had access t o posture before onset of clinical symptoms. Predominant clinical sign in a ll hones was moderate to severe acute colic with apathia, reduced gut motil ity, absence of defaecation, and gastrointestinal reflux (1-1.5 L/h). Recta l examination revealed typical findings, absence of faecal bails and increa sed amounts of fibrin strands in the rectum and a secondary impaction of th e ascending or descending colon. Further typical signs of all hones were an increased heart rate (76 +/- 15 /min) and fever (38.7 +/- 0.26 degreesC). in addition, hypersalivation (n=5) and muscle tremors (n=5), and localized or generalized sweating (n=3) were observed. Haematology and blood chemistr y did not contribute to diagnosis. All six horses were treated symptomaticaly. Several days after hospitalisat ion however they had to be euthanized because of progression of the disease . The clinical diagnosis of gross sickness was supported by the results of necropsy and histologic examination. Furthermore, degeneration of neurons s een at immunhistochemistry confirmed the diagnosis.