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  Discussion on Is Eucalyptus toxic?
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Member:
Sumnera

Posted on Wednesday, Apr 30, 2003 - 11:58 am:

I know this is an old post, but I just wanted to add to it in case there was anyone out there who was concerned about Eucalyptus trees.

I live on the central coast of California where Eucalyptus trees are very common. The boarding stable where I keep my horses is surrounded by them. The leaves, twigs, branches and pods all fall into the corrals and occasionally the water troughs. Some horses chew the bark on the trees. We've never had a horse poisoned or any other problems related to the presence of Eucalyptus trees.
Member:
parfait

Posted on Tuesday, May 15, 2007 - 1:53 pm:

Dr. O,

There's some confusion over the Eucalyptus cladocalyx (it's native to Australia but common in CA and Hawaii). I have seen on several sites that it's one of the plants that converts to cyanide if dried or crushed. This site is the best: https://www.ivis.org/special_books/Knight/chap1/ivis.pdf
Anyway, I was searching as my gelding has a huge tree over his run and it DrOpped a bunch of leaves recently (which are now gone) and all of his legs are swollen. He also has midline edema. I was wondering if that was the cause as I couldn't think of any other reason for it. I have also read some stuff about poisoning Aussie cattle...

Can you help on this? The horse is not used to eating this plant. My local vet didn't know as we have one of the few in AZ.
Member:
zarr

Posted on Tuesday, May 15, 2007 - 6:07 pm:

kerry, there are homemade fly spray reciepes that use eucalyptus oil so I sure hope not will check more for sure now. cindy
Moderator:
DrO

Posted on Wednesday, May 16, 2007 - 9:04 am:

Hello kerry,
I don't think peripheral edema, a common problem in horses, is a likely primary symptom of cyanide poisoning. For more information on edema and swelling and its diagnosis see, Diseases of Horses » Skin Diseases, Wounds, and Swellings » Swellings / Localized Infection / Abscesses » Diagnosing and Assessing Swellings in Horses.

Here is a review of the cyanogenic potential of Eucalyptus. Unfortunately it does not give us the potential for poisoning in horses and I cannot find any case reports. There is a report of poisoning in a herd of goats.
DrO

Tree Physiol. 2000 May;20(9):591-598.
Temporal and spatial variation in cyanogenic glycosides in Eucalyptus cladocalyx.
Gleadow RM, WooDrOw IE.
School of Botany, University of Melbourne, Victoria 3010, Australia.

The release of hyDrOgen cyanide from endogenous cyanide-containing compounds in plants is an effective herbivore deterrent. We investigated temporal and spatial variations in cyanogenic glycoside concentration in greenhouse-grown seedlings and 6-year-old plantation trees of Eucalyptus cladocalyx F. Muell., which allocates up to 20% of leaf nitrogen to the cyanogenic glycoside, prunasin. The highest cyanogenic glycoside concentrations were in the young, developing vegetative and reproductive tissues. Both the overall cyanogenic glycoside concentration and the proportion of nitrogen allocated to cyanogenic glycoside decreased as tissues matured. Cyanogenic glycoside and nitrogen concentrations were similar at all positions on the leaf blade. There was no change in concentration of cyanogenic glycosides either diurnally or following wounding of the tissue, suggesting that these compounds are constitutive. Cyanogenic glycoside concentration varied seasonally in young leaf tips of field-grown E. cladocalyx, but not in mature, fully expanded leaves. Although some of the changes in cyanogenic glycoside concentration in young leaf tips may have been driven by changes in leaf nitrogen, there was a significant decrease in the proportion of nitrogen allocated to cyanogenic glycosides in young leaves during the summer, coinciding with the peak flowering period. Mobilization of cyanogenic glycosides may have occurred to provide nitrogen for reproduction. Most of the observed temporal and spatial variations in cyanogenic glycosides are consistent with the optimal use of resources, particularly nitrogen.
Member:
parfait

Posted on Wednesday, May 16, 2007 - 11:33 am:

Thanks Dr O.
Member:
parfait

Posted on Wednesday, May 16, 2007 - 11:54 am:

I just read your updated version--I hadn't bothered to read the article as I knew the old one by heart. The new article is excellent and very clear--practically a flow chart--nice!

Thanks again,

KB
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