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Juglans Nigra
- Black Walnut - Toxicosis in Horses
from: Veterinary Toxicology, Beasley V. (Ed.) International Veterinary
Information Service, Ithaca NY (www.ivis.org), 1999; A2625.0899
Note 1: This does not seem to be a problem with cattle. The USDA
endorses the use of Black Walnut bark for cattle bedding (http://www.fpl.fs.fed.us/documnts/fplrn/fplrn091.pdf).
Note 2: The toxic component of Juglans nigra, Juglone, is found in
other members of the walnut family including English walnuts, butternuts,
hickories, and pecans.
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Source
- Black walnut (Juglans nigra) is native to the eastern United
States, growing in the well-drained soil of the Appalachians and midwestern
valleys.
- The wood is commonly used and prized as furniture and gun barrel stocks.
- The resultant shavings and sawdust are shipped wherever a market exists.
Toxic Principle
- Preliminary investigative work in an effort to identify the causative
agent in walnut shavings laminitis was focused on "juglone"
(5-hydroxy-1,4-naphthaquinone), a naphthoquinine toxin found in members of
the walnut and hickory family.
- Juglone is also present in other members of the walnut family (Persian or
English walnuts, butternuts, hickories, and pecans).
- The structure of juglone is as follows.
Juglone
- Experimental attempts to reproduce the clinical syndrome by using juglone
were less than convincing.
- Experiments administering juglone in differing concentrations orally and
topically (distal metacarpus to coronary band) have inconsistently produced
clinical signs but not full-blown laminitis. Intravenous administration to
one horse produced acute pulmonary edema and death.
- Juglone is believed to be responsible for the poor success of other
vegetation beneath black walnut trees but is not likely to be
responsible for black walnut toxicosis of horses.
Toxicity
- Field reports indicate that laminitis has occurred when bedding contained
only 5 - 20% black walnut shavings.
- All parts of the tree may be toxic including the heartwood, leaves, roots,
and bark.
- Every black walnut tree does not have naturally occurring toxicity,
implying environmental factors may alter the tree's toxicity.
- The toxin appears to act by causing a sensitization of vessels of the foot
to the effects of adrenergic agonists such that acutely there is a reduction
in the function of blood flow to the foot that reaches the dorsal laminae.
Signs
- Rapid onset, 12 - 24 hours after exposure.
- Commonly, several if not most horses of a group may be acutely affected
with laminitis.
- Depression.
- Laminitis.
- Laminitic stance. Can see acute and/or chronic laminitis, and in either
case, there can be rotation of P-3.
- Reluctance to move, resistance to attempts to pick up feet.
- Digital pulse evident, elevated hoof temperature in affected digits.
- Slight to moderate edema in limbs, from carpus and tarsus down.
- Increased respiratory rate and effort.
- Increased borborygmi.
- Elevated temperature and pulse.
Lesions
Necrosis of dorsal laminae followed by mitotic activity in an effort to repair
the damage.
Treatment
Laminitis Treatment Can Include:
- Phenylbutazone.
- Soft bedding (damp sand), or padded shoe.
- Removal of shoes.
- Acepromazine,
or a more specific alpha blocker (i.e., prazosin),
to restore circulation to the dorsal laminae and possibly heparin to prevent
microthrombi formation.
Prevention
Do not use fresh black walnut shavings for bedding.
Black Walnut, Juglans nigra L.
Growth Form - Large tree up to 150 feet tall; trunk diameter
up to 5 feet; crown broadly rounded; trunk straight, columnar, not buttressed at
the base.
Bark - Black, thick, deeply furrowed.
Twigs - Stout, greenish or orange-brown, hairy, smooth and gray;
pith brown, divided by partitions; leaf scars alternate, shield-shaped,
elevated, with 3 bundle traces.
Buds - More or less rounded at the tip, pale brown, soft,
hairy, up to 1/2 inch long.
Leaves - Alternate, pinnately compounded, with 15 - 23
leaflets; leaflets up to 3 1/2 inches long and 1 1/2 inches wide, broadly
lance-shaped, pointed at the tip, rounded at the asymmetrical base, toothed
along the edges, yellow-green and smooth on the upper surface, paler and hairy
on the lower surface, turning yellow in the autumn.
Flowers - Borne separately but on the same tree, appearing when
the leaves are partly grown, the staminate several in thick, yellow-green, hairy
catkins, the pistillate much fewer in small spikes, neither of them with petals.
Fruit - In groups of 1 or 2, spherical, up to 2 inches in
diameter, green or yellow-green, slightly roughened, the husk thick, the nut
very hard, oval, dark brown, deeply ridged, the seed sweet.
Wood - Hard, heavy, course-grained, dark brown.
Uses - The wood is used for furniture, interior finishing,
cabinets; the nuts are edible.
Habitat - Rich woodlands.
Range - Massachusetts across to Minnesota, south to Texas, east
to Florida.
Distinguishing Features - The Black Walnut is recognized by its
characteristic buds, its chambered pith, and its fruits.
 
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