It has long been established that Black Walnut (tree) is very toxic to
the horse, in any form (leaves, shavings, etc.)  I cannot find through
web searches, and local cooperative extensions, and Cornell,  whether
or not other species of walnut are also toxic to the horse, like
English walnut.  Have Carpathian English walnut on my property (and
horses).  Really need to know.

Dear paxvobiscum-ga;

Thank you for allowing me an opportunity to answer your interesting question.

The toxic phenolic compound in Black Walnut is called "Juglone" (5
hydroxy-1, 4 napthoquinone).  It is found in the bark, wood, nuts, and
roots of black walnut (Juglans nigra). Most members of the Walnut
family (Juglandaceae) produce this chemical including Black walnut,
pecan, hickory and others members of the family including Carya,
Engelhardtia, Juglans, Platycarya and Pterocarya. Black walnut and
butternut produce so much of the compound that plants growing nearby
can become poisonous just by glowing in the vicinity of the tree.
Other species including English walnut, pecan,
shellbark/shagbark/bitternut hickory, produce such small quantities of
juglone that toxic reactions in other plants are rarely observed.
Black walnut is the most toxic but these other plants still pose some
direct risk to horses as well.

I hope you find that my research exceeds your expectations. If you
have any questions about my research please post a clarification
request prior to rating the answer. Otherwise, I welcome your rating
and your final comments and I look forward to working with you again
in the near future. Thank you for bringing your question to us.

Best regards;
Tutuzdad ? Google Answers Researcher


OTHER INFORMATION SOURCES

Recommended reading:

HORSE OWNER'S FIELD GUIDE TO TOXIC PLANTS
http://www.ruralheritage.com/bookstore/catalog_details.cgi?recno=305

ONTARIO MINISTRY OF AGRICULTURE, FOOD AND RURAL AFFAIRS
?WALNUT TOXCITY?
http://www.gov.on.ca/OMAFRA/english/crops/facts/info_walnut_toxicity.htm

UNIVERSITY OF IDAHO
http://www.cnr.uidaho.edu/extforest/ATC4.pdf#search='Carpathian%20English%20walnut%20juglone'

OHIO STATE UNIVERSITY
http://ohioline.osu.edu/hyg-fact/1000/1148.html



SEARCH STRATEGY


SEARCH ENGINES USED:

Google ://www.google.com




SEARCH TERMS USED:


Walnut

Horses

Toxic

Juglone

---

Clarification of Answer by tutuzdad-ga on 07 Aug 2005 11:26 PDT

Thank you for the generous tip!

[Tutu says "Hey back atcha"]

tutuzdad-ga

tutuzdad - thanks.  I get from reading all the links, that ASSUMING
that horses in close proximity to the Carpathian are all right, is
unwise, especially due to the spread of the root systems possibly
affecting nearby growth, and to the fact that the horses can't be
protected at all from possible effects of pollen drift.

The gorgeous trees must go.  However, references to rotting root
systems after trees cut down, may not hold water either.  Lost a
mature tree to mini-tornado, then it regrew from old root system. 
Horses ate leaves of new growth, killed the young tree, and now it is
AGAIN regrowing.

Another VERY mature tree, had no leaves for two seasons (late frost
problem).  That same tree this year, put out about 1/3 of full set of
leaves.  They basically refuse to die, probably BECAUSE of the extent
of the root systems.  May have rather large problem trying to
eradicate. You folks knocked me off the fence on this one. Had hoped
could let trees live. Am buying field guide you folks suggested, as
well.

Say hi to "tutu" for me.

I am most impressed with the help I got from you, and the helpful
"commenters" on Google Answer.  Will definitely use this service
again.

Pax --

It appears that the risk is with black walnut trees and shavings (the
latter sometimes finding its way into bedding).  Agriculture Canada
only lists the black walnut as toxic:

Agriculture Canada
"All Poisonous Plants"
http://www.cbif.gc.ca/pls/pp/ppack.list?p_sci=comm&p_type=all&p_x=px

The active element in black walnut is a growth inhibitor called "juglone".

Meadowsweet Acre Herbs (Google cached link -- live link was dead early on Aug. 6)
http://64.233.179.104/search?q=cache:mWniq1zMgzQJ:www.meadowherbs.com/toxic.htm+walnut+horse+toxic&hl=en

You might want to check with an arborist to see if your Carpathian
English walnut trees have any significant amount of juglone.

Best regards,

Omnivorous-GA

Pax:  
My research mostly tracks with Omni's:

"Other trees closely related to black walnut also produce juglone,
including butternut, English walnut, pecan, shagbark hickory, and
bitternut hickory. However, all produce such limited quantities
compared to the black walnut that toxicity to other plants is rarely
observed."
http://www.wvu.edu/~agexten/hortcult/fruits/blkwalnt.htm

Carpathian walnuts are just cold-hardy strains of Persian, or English,
walnuts (Juglans regia L.), and are in the Section Juglans of the
species Juglans.
Black walnuts are in the Section Rhysocaryon of the species Juglans. 
They are a different genus from the English walnuts.
http://www.uga.edu/fruit/walnut.htm

Caution, however:  English walnuts are often grafted onto black walnut
rootstocks, and it is unclear whether that would affect the leaves of
the English walnut:
http://drclarkia.com/juglans_nigra.htm

This site (a newsletter put out by the Valley Horse Owners Association
in California?s San Fernando Valley) states that English walnuts ARE
toxic to horses.  But since it does NOT mention black walnuts, I
wonder whether the newsletter was confusing English walnuts with
black.  There is a picture of the plant they warn against, so you
might want to take a look:
http://www.vhoa.org/newsletter/articles/200401_newsletter_04.htm

This site (discussion forum) includes a comment by a person who states
that she has had her horses in pasture with English Walnuts for 9
years with no problems, even when the horses eat the leaves; but she
does take the horses off that pasture when the nuts fall, just as a
precaution:
http://www.endurance.net/RideCamp/archives/past/99/24/msg00506.html

None of this was definitive enough for me to post as an Answer, so
perhaps someone more knowledgeable will come along and add to what
Omni and I have learned.  Good luck!

Thanks for the help.  Sounds like the answer is "MAYBE".  Frustrating.
 Perhaps there is not a definitive answer at this time, but after
having read some of the material in the links, I guess I wouldn't want
them injecting horses with the questionable substance, just to see if
something happens.

Thanks much Omni and Hagan.  From here, will try to find out about the
root stock on my particular trees before I cut them down.

The difficulty with this question is that it's tough to prove a
negative. It is unlikely that if other kinds of walnuts are toxic to
horses that literature would mention this. The focus of the sort of
literature that will be helpful to you is to point out plants that ARE
toxic plants. (For example, see "Toxic Plants in Your Horse Pasture:" 
http://www.ruralheritage.com/vet_clinic/plants_toxic.htm )

What I would recommend is that you get a good book on toxic plants and
horses. Here are two recommendations:

* 'Horse Owner's Field Guide to Toxic Plants,"
http://www.amazon.com/exec/obidos/tg/detail/-/0914327623/qid=1123361397/sr=8-1/ref=pd_bbs_1/103-8319960-2919819?v=glance&s=books&n=507846

* "A Guide to Poisonous Plants for Horses," 
http://www.amazon.com/exec/obidos/tg/detail/-/0851316980/qid=1123361397/sr=8-2/ref=pd_bbs_2/103-8319960-2919819?v=glance&s=books&n=507846


If I were in your position, I would buy the first book.

I hope this helps,
Kristina

You are most welcome.