Indigofera spicata (creeping indigo) poisoning of three ponies

Abstract

Three ponies continuously grazed a pasture containing an estimated 24% Indigofera spicata (wet weight basis) for 4-6 weeks in April and May 2004. They developed ataxia, paresis, depression, muscle fasciculations, dysphagia, ptyalism and halitosis. Two also developed corneal opacity. One pony recovered with supportive treatment, but the other two were euthanased and necropsied. Neuropathology was not present in either case, but both livers had periacinar and periportal lymphocytic infiltrations and hydropic degeneration of mid-zonal hepatocytes, with mild to moderate periacinar necrosis also evident in one. The I. spicata contained 2.66 mg 3-nitropropionic acid (3-NPA)/g dry matter and 1.5 mg indospicine/g dry matter. Indospicine, but not 3-NPA, was detected in serum from both of the euthanased ponies and indospicine was detected in heart, liver and muscle from the one pony in which this assay was performed. The clinical syndrome closely resembled 'Birdsville horse disease' caused by I. linnaei and was similar to that reported in horses poisoned by the closely related species I. hendecaphylla and to 3-NPA poisoning of other animals, including humans. 3-NPA is thought to cause this neurological syndrome. To our knowledge, this is the first authenticated report of I. spicata poisoning in grazing animals. We also report here the first published evidence that 3-NPA and indospicine exist in naturalised I. spicata in Australia and of the formation of indospicine residues in tissues of animals grazing paddocks infested with I. spicata.

The Occurrence and Toxicity of Indospicine to Grazing Animals

“…Horses consuming I. linnaei and I. spicata appear resistant to the hepatotoxic effect of indospicine [1,11]. Microscopic examination reveals only mild liver lesions consistent with descriptions of indospicine-related hepatopathy, including periacinar and periportal lymphocytic infiltrations, hydropic degeneration of mid-zonal hepatocytes and multifocal periacinar necrosis [11].…”

“…Microscopic examination reveals only mild liver lesions consistent with descriptions of indospicine-related hepatopathy, including periacinar and periportal lymphocytic infiltrations, hydropic degeneration of mid-zonal hepatocytes and multifocal periacinar necrosis [11]. Horses however don't escape embryolethality indospicine effects, and abortion is commonly observed in mares consuming I. lespedeziodes in Brazil [29].…”

“…These species names appear interchangeably in early literature and it was not until 1993 that these were shown to be 2 separate species [10]. It is thus difficult to ascertain with any certainty which of these species was actually used in early studies unless herbarium voucher specimens are examined [11]. Retrospective inspection of herbarium data has however established that the study by Hegarty and Pound utilized specimens of both species, and that indospicine was determined in both I. spicata and I. hendecaphylla in their work [11].…”

“…Species in which high levels of indospicine have been determined in foliage (in excess of 500 mg/kg DM) include I. hendecaphylla [4,11], I. linnaei [12,13], I. lespedezioides [7,14,15], I. spicata [4,11,[13][14][15][16], I. vicioides [9] and I. volkensii [7]. Indeed levels up to an exceptional 1.2% (DM basis) have been reported in I. spicata [7].…”

“…Equine neurological syndromes known as "Birdsville horse disease" in Australia [11] and "Grove disease" in USA [60] are attributed to consumption of Indigofera plant species but do not relate to indospicine toxicosis. Indigofera species particularly I. hendecaphylla, I. linnaei and I. spicata have been shown to contain glucose esters of 3-nitropropanoic acid (3-NPA) co-occurring with indospicine, and 3-NPA is believed to be the toxin responsible for the neurological syndrome seen in horses (but not ruminants) consuming these plants [11,[61][62][63].…”