14/10/2026
🍁Sycamore Toxicity and Atypical Myopathy in Horses
🧬Seeds, leaves and seedlings from sycamore trees contain the toxin Hypoglycin A (HGA), which can cause atypical myopathy in grazing horses.
💉Following ingestion, HGA disrupts normal energy production within muscle cells, resulting in severe muscle damage. Clinical signs may initially resemble "tying-up", with affected horses appearing stiff, uncomfortable and reluctant to move.
🌡️As the disease progresses, horses may develop marked weakness, muscle tremors and dark red or brown urine. Additional signs include a fast or irregular heartbeat, increased respiratory rate, depression, sweating and a characteristic head-down posture.
🩺Clinical deterioration can occur rapidly, with signs developing within hours of toxin ingestion. Prompt veterinary attention is essential, as early intervention can improve the chances of survival.
🚑Despite treatment, atypical myopathy carries a guarded prognosis, with reported survival rates of approximately 30-40%. Many affected horses require intensive supportive care and hospitalisation, and recovery may take several months.
🔍Prevention remains the most effective strategy. Sycamore seeds, seedlings and fallen leaves should be removed from grazing areas wherever possible. Providing supplementary forage, such as hay or haylage, may help reduce the likelihood of horses grazing in contaminated areas. Consider relocating horses to alternative pasture during periods of high risk, particularly in autumn when seeds and leaves are shed and in spring when seedlings emerge.
🌳It is important to note that HGA concentrations vary considerably between seeds, seedlings and leaves, as well as between individual trees and even within different parts of the same tree. The Royal Veterinary College offers diagnostic testing to determine HGA concentrations in sycamore samples, which may assist with risk assessment and pasture management decisions.
👉If you have any questions or cause for concern, you can contact us on 0131 664 5606.