FieldDxEquine Grass Sickness (Equine Dysautonomia, Grass Disease, and Mal Secco)Clinical signs, differential diagnosis, treatment and prevention in horses.
Overview
A serious disease of horses with widespread degeneration of the autonomic nervous system; the exact cause is still not established. Unknown; a leading theory implicates toxicoinfection with Clostridium botulinum type C acting within the GI tract, but this is unproven, and access to green grass is a consistent risk factor.
Clinical signs
- Gastrointestinal hypomotility and ileus.
- Ptosis, giving drooping eyelashes.
- Rhinitis sicca, a dry nose.
- Anorexia and profound cachexia.
- Tachycardia without apparent pain.
- Dysphagia and oesophageal dysfunction.
- Patchy sweating and muscle fasciculations.
- Tucked-up stance.
Predisposing factors
- Access to green grass.
- Horses aged 2-7 years.
- Animals kept entirely at grass.
- Spring, when incidence peaks.
Treatment
- Acute and subacute cases do not survive and should be euthanased.
- Supportive nursing for carefully selected chronic cases only.
- High-energy, high-protein feeds that are easy to swallow.
- Clean the nose with warm water.
- About 70% of selected chronic cases recover.
Drugs mentioned: Cisapride
Prevention
1. Limit grazing on pasture with a history of cases. 2. Stable at-risk horses for part of the day. 3. Avoid disturbing pasture and soil. 4. Reduce soil exposure and close grazing. 5. Keep the diet consistent. 6. Co-graze with ruminants. 7. Keep pasture grass cut. 8. Remove droppings by hand. 9. Feed supplementary forage.
Source
MSD Veterinary Manual — Equine Dysautonomia (accessed 2026-07-31)
Condensed and attributed, never reproduced whole. Open the full entry in the app.