Suspected marsh mallow (Malva parviflora) toxicosis in ponies-Case cluster including an asymptomatic survivor

There is limited published information on Malva parviflora toxicosis in horses. Four previously reported cases all resulted in death or euthanasia. The aim of this cluster investigation was to describe historical, clinical and clinicopathological findings of four ponies with suspected M. parviflora toxicosis and compare these to previously reported cases. Historical, clinical and clinicopathological findings were collated. Ponies were grazing pasture of approximately >90% M. parviflora. Pony 1 died rapidly without veterinary examination. Pony 2 was examined for prolonged recumbency attributed to severe myopathy and was subjected to euthanasia. Ponies 3 and 4 remained clinically normal. Pony 2 displayed markedly increased plasma creatine kinase (CK) and aspartate aminotransferase (AST) activities and cardiac troponin I (CTnI) concentration. Pony 3 had moderately increased plasma CK and AST activities and normal plasma CTnI concentration. Pony 4 had moderately increased plasma AST activity, with normal plasma CK activity and CTnI concentration. Plasma acyl carnitine profiles of Ponies 2 and 3 were consistent with previous suspected cases of equine M. parviflora toxicosis, but Pony 4's acyl carnitine profile was not different from healthy control horses. Pony 2 was typical of previously reported cases of M. parviflora toxicosis, but Pony 3 did not develop clinical signs despite a consistent acyl carnitine profile. Pony 4 likely did not have M. parviflora toxicosis. The findings of Pony 3 suggest M. parviflora toxicosis can be subclinical, and survival is possible in such cases. Further work is needed to determine the progression of disease from M. parviflora ingestion.