Outbreak of ragwort (Senecio jacobea) poisoning in horses.

The research investigates an occurrence where a quarter of horses on a farm died from a brain condition caused by ragwort poisoning, with symptoms usually associated with liver damage. It was suspected that the toxic substances causing the condition came from the pasture the horses grazed on rather than their hay. Blood tests showed that high levels of a specific enzyme, Gamma Glutamyl Transferase (GGT), can indicate early liver damage, though not all horses with this indicator went on to develop the condition.

Research Context

• This research was prompted by an unusual incident where 5 out of 20 horses on a single farm died due to acute hepatic encephalopathy — a severe brain condition linked to liver damage — which was subsequently identified as ragwort toxicosis.
• Ragwort (Senecio jacobea) is a common plant found in pastures that can cause serious liver and brain damage in horses if ingested in significant quantities.

Source of Ragwort Exposure

• Upon investigation, the researchers proposed that the primary source of ragwort toxic alkaloids — the poisonous substances responsible for the condition in horses — was likely the pasture land rather than the hay fed to the horses, though the evidence supporting this conclusion was circumstantial.

Gamma Glutamyl Transferase (GGT) as an Indicator

• The study also focused on the incidence of elevated plasma levels of an enzyme known as Gamma Glutamyl Transferase (GGT) in the horses.
• This enzyme, when present in large quantities, is traditionally regarded as an early sign of liver damage.
• Efforts were made to measure this enzyme on three separate occasions in the surviving, ragwort-exposed horses to evaluate the effectiveness of GGT as an early indicator of ragwort toxicosis.

Findings and Implications

• The research found that elevated GGT levels did appear to be a useful indicator of early liver damage.
• A critical observation, however, was that not all horses that exhibited elevated GGT levels went on to develop clinical disease, indicating that while GGT can serve as a warning sign, it does not necessarily mean a horse will suffer acute hepatic encephalopathy.
• The findings of the study underline the importance of regular monitoring of GGT levels in horses to ensure early detection of potential liver damage, particularly in environments where ragwort exposure may be a risk.