An herb that is increasingly popular among urban foragers, has been linked to fatal heart and muscle disease in horses.

Marsh mallow (Malva parviflora) is native to southern Europe, North Africa and Asia but has long been naturalized in the continental United States and Australia. Also called “cheese weed” because of the round, yellow seedpods it bears, marsh mallow is said to have a mild flavor and is used in salads and stews.

However, the plant is potentially dangerous to horses, a fact underscored by a recent journal report that describes the case of four horses sickened after eating large amounts of marsh mallow. The horses, which were kept on the same farm in Victoria, Australia, quickly developed muscle fasiculations, irregular heartbeats and sweating after ingesting the herb. Eventually, all died or were euthanatized.

Postmortem examinations revealed damage to heart and skeletal muscles and abnormally high serum concentrations of certain acylcarnitines, products which help convert fatty acids into energy.

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The researchers say these findings suggest that ingestion of marsh mallow can cause toxicosis similar to the human genetic condition known as “very long chain acyl-CoA dehydrogenase deficiency.”

Reference: “Evidence for marsh mallow (Malva parviflora) toxicosis causing myocardial disease and myopathy in four horses,” Equine Veterinary Journal, June 2016

This article first appeared in EQUUS issue #468

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