Macadamia Toxicity in Dogs
Sourced from: Sub-Tropical Fruit Club of Qld newsletter Aug Sept 2002
After attending a weekend of talks at Fairhill Nursery
last year where I caught up with Nan & Hugh Nicholson (they wrote
that excellent series of rainforest books) Nan mentioned that in
certain species of Macadamia the kernels contained traces of cyanogenic
glycosides. This was the first I had heard about toxicity in
Macadamias and thought I would go looking for other sources of
information to do an article for our newsletter. Our previous Guest
Speakers Merv & Elwyn Hegarty also knew about it and sent me some
detail on the subject. The final piece of information came while I was
attending a lecture by Dr. Ross McKenzie on "Cyanide, Strychnine Bush
and other poisonous hazards in the Queensland flora". He sent me an
article that appeared in Australian Vet Practitioner 30(1) March 2000
and to summarize:
Plants in the genus Macadamia (family Proteacae) are endemic to eastern Australia (seven species) and Sulawesi in Indonesia (one specie) (Gross 1995) Macadamia tetraphylla, M integrifolia
and hybrids of these species – variously known as the Macadamia Nut
tree, Qld. Nut tree or Bopple Nut tree are cultivated in Australia,
Hawaii and elsewhere for the edible kernels. Some kernels of these
species contain traces of cyanogenic glycosides while the kernels of M. ternifolia and M. whelanii
contain significant amounts of cyanogenic glycosides, are bitter and
not currently used as human food (Aboriginees would remove the toxins
before eating them (Gross 1995).
In the clinical study, thirteen
adult dogs of both sexes, various ages and at least five different
breeds developed sudden onset of various combinations of either
paralysis, pain in the hindquarters, listlessness, limping 6-24 hours
after eating several kernels etc. with one Rottweiler being given 2
tablespoons of macadamia butter. All dogs recovered within 24
hours.
The close association between ingestion of kernels and
the onset of the syndrome in dogs and the consistent signs displayed
among cases strongly support the hypothesis that toxicity from a
chemical or chemicals in the kernels was responsible for the syndrome.
Such chemicals may well be part of the plant’s defence system
protecting its genetic material from attack by insects or microbes. The
only known toxins in Macadamia
spp. are cyanogenic glycosides. In one case where roasted kernels were
fed, it indicates that heat does not denature the toxin or toxins.
Given
the widespread consumption of Macadamia kernels by humans and the lack
of reports of subsequent poisoning, this syndrome appears to be a
further illustration of the differing reactions of mammalian species to
plant toxins. Dogs and humans for example differ significantly in their
likelihood of being poisoned by theobromine in chocolate (from Theobroma cacao) and their susceptibility to N-propyl disulphide and thiosulphates in onions (Allium cepa). Dog owners should be warned not to regard their animals as "small humans". As M. ternifolia
is native in the area where I live, I rang our local Veterinary Clinic
which has a large country practice (the Vet is an ex-President of the
Australian Veterinary Association) and they said they have never come
across this syndrome in their practice. I am a little surprised by this
as our "Chuck" (actually – Charles Henry Robert Backhouse - the Bull
Terrier) who actually belonged to the neighbour but lived at our place
during the day could crack an unshelled nut with his teeth – loved them.
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