Hepatotoxicity to dogs of horse meat contaminated with indospicine

Abstract

An outbreak of liver disease which killed more than 30 dogs at Alice Springs was associated with feeding meat from horses, some of which had developed Indigofera linnaei poisoning (Birdsville horse disease). Affected livers were small, nodular and yellow. There was associated jaundice, ascites, elevation of alanine aminotransferase levels in serum, a tendency to bleed, and signs of hepatic encephalopathy. Histologically, livers showed periacinar necrosis, collapse and haemorrhage, with severe swelling, vacuolation and cholestasis in remaining hepatocytes. Indospicine, a toxic amino acid found in the genus Indigofera, was detected in samples of suspect horsemeat. Experimental feeding of horsemeat containing 16 mg indospicine/kg for 32 days produced periacinar necrosis and hepatocellular swelling in 2 dogs, although neither died nor showed clinical illness. In another experiment, intakes of as little as 0.13 mg indospicine/kg bodyweight/day for 70 days produced periacinar liver lesions, and indospicine concentrations in serum, muscle and liver rose during this period to 3.9, 7.9 and 17.5 mg/kg, respectively. It was concluded that meat from horses grazing I. linnaei can be hepatotoxic for dogs, and that this toxicity may be related to its indospicine content.

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].…”

“…It is seemingly not readily metabolized by mammalian systems and accumulates as persistent residues in all tissues of animals consuming a diet containing the amino acid. Indospicine has been shown to accumulate in the tissues of horses [1,42,43], cattle [44] and goats [45] consuming I. linnaei, and in rabbits fed I. spicata seed [12]. The persistence of these residues has been demonstrated in experimental studies and tissue indospicine levels were still detectable several months after the cessation of feeding Indigofera plant material in horses [43], cattle [44], goats [45] and rabbits [12].…”

“…Interestingly, even though unaffected by the hepatotoxic effects of indospicine, horses consuming Indigofera plants are known to accumulate indospicine in their tissues [1,11]. Indospicine accumulation occurs in all tissues including muscle and is residual.…”

“…Indospicine accumulation occurs in all tissues including muscle and is residual. Fatal hepatotoxicity has occurred in dogs fed indospicine-contaminated meat from horses that had grazed I. linnaei in central Australia [1]. As a consequence, the Northern Territory of Australia Meat Industries Act [66] bans the slaughter of horses, donkeys, mules or hinnies for human consumption if the animals are exhibiting signs of Birdsville horse disease (I. linnaei poisoning), or for pet food if these animals originate from an area in which Birdsville disease occurs.…”

“…which in recent decades has gained notoriety for its ability to form persistent and sometimes toxic residues in tissues of grazing animals. Ingestion of indospicine-contaminated horse meat [1] and more recently camel meat [2] has resulted in the secondary poisoning of dogs which are particularly sensitive to indospicine hepatotoxicosis. The impact of this plant toxin on the health and production of grazing animals per se has been less widely documented and is the focus of this review.…”