Common Name
Black walnut
Botanic Name
Juglans nigra
Plant Family
Black walnuts are often planted as wind breaks, and along fence rows.
Black walnuts are found from North Dakota and Minnesota , south to Oklahoma and Missouri
Animals Affected
Horses, dogs
Black-walnut tree
Toxic Principle
The toxic principle in black walnuts responsible for causing laminitis and acute lameness in horses is not known for certainty. Juglone, a naphthaquinone was considered a likely toxin, but water extracts without juglone from black walnut wood can experimentally produce laminitis in horses. It is now suspecteded that a component in the water extracts stimulates a systemic inflammatory response that causes the laminitis. Black walnut, hickory, butternuts, pecans and English walnuts contain juglone, an allelopathic substance that is secreted by the roots of the tree to inhibit the growth of other plants. It is not certain whether large doses of juglone will produce the typical severe laminitis associated with horses that are kept on bedding containing black walnut shavings.
Large trees with rough brown bark, and leaves to 50 cm long with 11-17 hairless leaflets. The male flowers are catkins up to 12 cm. in length, while the female flowers are 1-2 cm. long. The fruits are pale, yellow-green, turning brown as they ripen. The hard nut is up to 4 cm. in diameter.The heart wood of the trunks is dark brown to black and is prized as wood for furniture making etc.
Edema of the lower legs, and lameness due to laminitis. If affected horses are removed from the source of the black walnut shavings early enough, and treated for the signs of laminitis they recover without the severe consequences of hoof deformity and third phalanx rotation.
Remove the animal from the walnut shavings immediately, and wash the horse's legs with soap and water to prevent further absorbtion of any toxin. If the horse is lame and showing signs of laminitis, it should be placed in a sand stall and treated by a veterinarian as soon as possible. Pain relief, in the form of non-steroidal, anti-inflammatory agents such as phenylbutazone or flunixin meglumine should be administered. Drugs such as adrenergic blockers (prazosin) and calcium channel blockers (nifedipine) may be beneficial in reducing the laminitis.
Nervous System
Convulsions may be seen in dogs and other animals eating moldy walnuts
Laminitis resulting from using black walnut shavings as bedding.
Special Notes
Wood shavings with as little as 20% black walnut shavings will induce laminitis. Shavings from black walnut and Butternut (Juglans cineraria) should not be used for horse bedding, especially if the shavings are fresh. Well aged shavings pose little or no risk as bedding for horses. English walnuts (Juglans regia) contain far less juglone than black walnuts (Juglans nigra)and pose less risk to horses. Fallen walnuts that are moldy (Penicillium spp.) can contain the mycotoxin Penitrem A that is poisonous to dogs and other animals that eat the moldy walnuts. Dogs can develop convulsions a few hours after eating the moldy walnuts. Hyperthermia, rapid breathing, urination and dilated pupils may also be seen in affeted animals. References 1. Ralston SL, Rich VA: Black walnut toxicosis in horses. J Am Vet Med Assoc 183: 1095 (1983). 2. Minnick PD, Brown CM, Braselton WE, et al: The induction of equine laminitis with an aqueous extract of the heartwood of black walnut (Juglans nigra). Vet Hum Toxicol 29:230-233 1987 3. Galey FD, Beasley VR, Schaeffer D, et al: Effect of an aqueous extract of black walnut (Juglans nigra) on isolated equine digital vessels. Am J Vet Res 51: 83-88 (1990). 4. Peroni JF et al. Black walnut extract-induced laminitis in horses is associated with heterogeneous dysfunction of the laminar microvasculature. Equine Vet J.37:546-551 (2005). 5. Richard JL, Bacchetti P, Arp LH. Moldy walnut toxicosis in a dog, caused by the mycotoxin, penitrem A. Mycopathologia 1981, 76: 55-58. 6. 7. Belknap, JK, Black Walnut Extract: An Inflammatory Model. Veterinary Clinics of North America: Equine Practice, 26 (1): 95-101 (2010).
Black walnut fruits
Wood shavings showing dark black walnut shavings