Pyrrolizidine alkaloid-induced liver disease in horses: an early diagnosis.

The research discusses the impact of pyrrolizidine alkaloids (PA) found in Senecio vulgaris on horses’ liver health, through an experiment where nine adult horses were fed alfalfa hay cubes containing the toxic component. All subjects showed significant liver disease, with most developing severe complications and eight dying or being euthanized. The study notably demonstrates that early signs in the form of dietary changes and weight loss appear before clinical signs of the resulting liver disease.

Study Setup

• The study involved nine adult horses being fed alfalfa hay cubes, containing about 10% of Senecio vulgaris, a plant species known for containing poisonous pyrrolizidine alkaloids (PA).
• The dosage of PA was established by a preliminary toxicosis approximation, where the amount that caused visible clinical symptoms in three horses was considered reference.
• This dosage was then adjusted according to each horse’s weight. Essentially, all horses consumed nearly the same amount of PA per kilogram of their body weight.

Resulting Dietary Changes and Weight Loss

• As soon as the horses’ diets were switched to the contaminated feed, a drop in feed intake was observed.
• This reduction in diet continued between 89 to 98 days of the experiment.
• All the horses experienced a decrease in body weight between 50 to 159 days, marking a significant directional change regarding their health status.

Liver Disease Development

• All nine horses developed liver disease after consuming an average of about 233 mg of PA/kg body weight.
• Initial indications of liver disease were ataxia (loss of control over body movements), decreased feed intake, and head pressing.
• Upon examination, megalocytic hepatopathy (an enlarged liver condition) was detected in the horses.
• The severity of liver abnormalities increased as more PA was consumed, and in most cases, these liver issues were significantly advanced before the appearance of the clinical signs of toxicity.

Mortality

• Eight of the nine horses either died naturally or had to be euthanized due to extreme suffering, indicating a high mortality rate from the intake of PA.
• No positive impact on survival was observed from treatment with branched-chain amino acids, although it appeared to reduce some neurological symptoms.
• Bile Acid (BA) concentrations in eight horses that died increased significantly. However, one horse, which developed hepatopathy and increased BA concentration, managed to survive with its BA concentration peaking at 33 mumol/L, before gradually reducing.
• The removal of a liver-detoxifying agent, sulfobromophthalein sodium, was not significantly impaired until the stage of advanced liver disease.