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This article was published in 1967
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INSTITUTE OF INSPECTORS OF STOCK OF N.S.W. YEAR BOOK.
Macrozamia Poisoning
P.J. HEALY, B.V.Sc., Veterinary Research Officer, Glenfield
Poisoning of humans and animals by parts of the cycad genus, Macrozamia, has often been reported in the literature. Two distinct syndromes have been associated with the ingestion of various parts of these plants. Under certain, as yet undefined, conditions ingestion of the fronds of Macrozamia spp. by cattle may result in the development of a peculiar posterior locomotor disorder. On the other hand starchy parts of cycads, such as the ovules of Macrozamia and Cycas spp. induce a hepato-gastro-intestinal disorder when consumed by humans or domestic animals.
The pathogenesis of the locomotor disorder in cattle has yet to be elucidated; in fact the pathology of this condition has only recently been the subject of investigation. Some preliminary investigations have revealed that there are degenerative changes in the spinal cords of chronic cases of this condition, in both field and experimentally produced cases.
Gastro-intestinal and hepatic dysfunctions, observed in humans and domestic animals, resulting from ingestion of ovules of Macrozamia spp. are a consequence of the presence of an unusual class of glycosides azoxyglycosides in the ovules. These glycosides are inactive biologically in the intact glycosides form, but following cleavage of the glycoidic bond by the intestinal flora, the aglycone so produced is toxic.
The aglycone, methylazoxymethanol, is a potent hepatotoxin. Studies with experimental animals have revealed that profound biochemical disturbances are evident in the liver within six hours of oral administration of the toxin.
Methylazoxymethanol is also an active carcinogen. Renal, hepatic and intestinal tumours have been induced in a variety of experimental animals by repeated oral administration of the glycosides.
Field cases of poisoning by the ovules of Macrozamia spp. occur sporadically in New South Wales. A typical example is that described by Seddon, Belschner and King (1931), involving a mortality of 30 per cent in a flock of 6000 Merino ewes associated with the consumption of ripe ovules of M. spiralis.
REFERENCE
Seddon, H. R., Belschner, H. G., and King, R. O. C. (1931) — NSW, Dept. Agr. Rpt. 6:70