Equine Grass Sickness (Equine Dysautonomia)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

Acute, subacute and chronic forms; acute and subacute cases are reported as fatal, and chronic cases about 50%.
Intestinal impaction and gastrointestinal stasis.
Tachycardia, depression or lethargy, and muscle tremors.
Hypersalivation, weight loss, drooping eyelids (ptosis) and rhinitis sicca.

Predisposing factors

Younger animals appear to be at higher risk, and horses are mostly kept outdoors in rural areas.
Incidence peaks in spring (April-May); more frost days and longer sunshine hours are linked to higher risk, and consistently high maximum temperatures to lower risk.
A move to a new pasture preceded one outbreak; buttercup-rich pasture and differences in soil minerals and gut fungi have been reported, but none is shown to be the cause.
Some stallions' offspring are at significantly higher risk, but a heritable basis is not confirmed.

Look-alikes to rule out

Equine Grass Sickness (Equine Dysautonomia, Grass Disease, and Mal Secco) Botulism

Treatment

No treatment addresses the underlying neuronal degeneration; management is entirely supportive, particularly careful high-energy feeding. Only mildly affected cases have a chance of survival.

Drugs mentioned: Cisapride

Prevention

This remains undefined in the uploaded documents.

Source

Veterinary Record, Harte T, Smith D, Moore J, Wells B (2025), via PubMed Central — Review of published research on primary dysautonomia of domestic animals (accessed 2026-10-29)

MSD Veterinary Manual — Equine Dysautonomia (accessed 2026-08-11)

A Textbook of the Diseases of Cattle, A Textbook of the Diseases of Cattle, Horses, Sheep, Pigs and Goat by ELSEVIER *A Textbook of the Diseases of Cattle

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