Evidence for marsh mallow (Malva parviflora) toxicosis causing myocardial disease and myopathy in four horses.

The research article discusses the investigation into the causes of toxicosis in four horses in the same farm that came about as a result of consuming a plant called Malva parviflora, commonly known as marsh mallow. The toxicosis led to severe muscle contractions, rapid heart rate, sweating, lying down for extended periods and eventually death or euthanasia. The research suggests that the presence of cyclopropene fatty acids found in the plant could interfere with the metabolism of fatty acids in horses leading to these symptoms.

Research Objective and Methodology

• The major objective of this research was to describe the historical, clinical, clinicopathological and pathological findings of the four horses suspected to have toxicosis caused by Malva parviflora. The researchers also wanted to explore the role of cyclopropene fatty acids (found in M. parviflora) and propose their mechanism for causing toxicosis.
• The research was carried out as a case series. The researchers reported the historical, physical examination, clinicopathological and pathological findings for each case.
• Two of the horses’ serum profiles were tested in order to ascertain if any similarities with atypical myopathy or seasonal pasture myopathy existed.
• The presence of cyclopropene fatty acids was examined in the serum of the two horses.

Results and Conclusion

• The results of this study showed that M. parviflora had been heavily grazed by the horses with little other feed available. A fast deterioration of health, severe heart disease and generalized muscle pathology were observed in the affected horses.
• Post-mortem examinations performed on three of the horses revealed acute, multifocal cardiac and skeletal muscle breakdown. Glycogen accumulation within the muscle cells, a typical sign for certain types of muscle diseases, was absent in one of the horses.
• The researchers found increased C14-C18 acyl carnitine concentrations in the horse cases when compared to controls, indicating interference with lipid metabolism.
• Study results also confirmed presence of cyclopropene fatty acids in the serum of the affected horses but not in the controls, suggesting the possible role of these components in the toxicosis.
• The conclusions drawn from these findings indicate a different cause than that of atypical myopathy or seasonal pasture myopathy which was initially suspected.
• The authors proposed that cyclopropene fatty acids in M. parviflora interfere with fatty acid β-oxidation in horses in negative energy balance, causing the clinical signs and abnormal acyl carnitine profiles.
• This type of interference is said to closely mimic the human genetic condition called very long chain acyl CoA dehydrogenase deficiency.