Understanding Black Walnut Shavings and the Risks to Horses

Identifying Black Walnut Trees

• These tall, straight trees with expansive crowns are easy to spot if you know what to look for. Black walnut wood is famous for its dark coloring and highly desired for furniture and woodworking. The heartwood, the central part of the tree, is especially dark in black walnut.

• They have a few distinguishing features that set them apart from other trees. First, their leaves are compound, meaning one “leaf” is a collection of smaller leaflets. There are 11-23 leaflets per leaf, and the edges appear to have ridges or teeth. Each leaflet is about 4 inches long and 1-2 inches wide, yellow-greenish in color on the top. Under the leaflets, the color pales, and they are hairy there, too.

• The other feature is the walnut itself. The fruit first appears as a green golf ball in the tree and turns dark brown or black as it ripens, eventually falling to the ground. Inside this shell is the edible, oily nut.

Black Walnut Toxicity to Horses

• We know that horses in contact with black walnut are at serious risk of poisoning, creating laminitis and colic. Research has confirmed that standing in black walnut shavings is dangerous. We also know that eating and even rubbing against this tree is hazardous.

• And there are two suspected primary culprits in black walnut trees – juglone and mycotoxins.

Shavings from these trees are toxic, and you may not be able to see them when mixed with other shavings. 

Understanding Juglone and Its Impact on Equine Health

• In the roots and wood of the black walnut resides a chemical called juglone, also referred to as juglans nigra. Juglone is thought to be the primary toxin involved in laminitis, colic, and other associated ailments. However, science tells us it’s more complicated.

• Researchers have discovered that laminitis happens when juglone is removed from black walnut and horses are exposed to the juglone-free extracts. This doesn’t exclude juglone as the primary toxin. It just means science can’t duplicate this exact process yet, or other factors must be included.

• In the trees, roots secrete juglone to inhibit other plants and trees from growing too closely.

Mycotoxins

• Mycotoxins are toxins excreted by mold, a type of fungi. Black walnut hulls, the golf ball containers for the walnut, love to harbor mold and, therefore, mycotoxins.

• A particularly terrible mycotoxin is penitrem A, which causes rapid nervous system dysfunction in horses. Problems include tremors, seizures, and neurological damage, even to the brain.

• Horses grazing on or near black walnut hulls are at risk. Ideally, there are no black walnut trees where your horses turn out or trail ride.

Black Walnut Shavings and Bedding

• Sawdust from mills is one way to source shavings for the barn. However, even the smallest amount can create a toxic reaction in your horse. Sawdust that’s 5% black walnut can create problems, and fresh shavings are more harmful than older shavings. But still toxic.

• It’s darn near impossible to discern black walnut shavings mixed with others. Alone, black walnut shavings will be darker, but combined with other tree types and moisture content, you will never be certain.

• You must trust that your sawdust or shavings supplier never processes black walnut trees.

Black Walnut in Pasture

• Black walnut trees can be harmful to horses in pastures, too

• The roots also release toxins, making an underground ring of toxins spread 50+ feet around the tree. Their fallen branches, nuts, and pollen also have toxic substances.

• One option is to fence off any trees, but it’s best to remove them. Fallen branches, leaves, and wayward walnut hulls can find their way out of any barriers.

How Does Laminitis Happen After Exposure?

• The toxins usually enter your horse via the skin, specifically the coronary band area and the lower legs, as they stand in bedding. Blood flow is altered, and because this happens where the hoof meets the leg, there is increasing pressure and damage inside the hoof, creating laminitis.

• This swelling and blood flow interruption is also why the lower legs tend to swell, too.

Signs of Black Walnut Toxicity in Horses

• Damage to the hooves happens within a few hours of exposure. You will find the usual signs of laminitis, like:

• • Increased digital pulses
  • Heat in the hooves
  • Swollen lower legs or stocking up
  • Lameness
  • Colic-like signs
  • Listlessness
  • Reluctance to move, turn, or showing a stiff and shortened gait when moving
  • Abnormal vital signs, like an increased pulse and respiratory rate
  • Fever

Diagnosis and Complications

• Your vet must see your horse ASAP for signs of colic or laminitis. Your vet will look for clinical signs and likely use hoof testers to assess where there’s pain in the hoof. The best way to get a complete view is via X-rays to determine what’s happening inside the hoof.

• With more information, you and your vet can help with pain management and reduce the likelihood of complications.

Founder – coffin bone rotation

• Founder is a terrible progression of severe cases of laminitis when the coffin bone starts to move inside the hoof. As the impaired blood flow damages the supporting laminae, the soft tissue connecting the hoof to the bones, the bones may begin to shift, twist, or otherwise sink.

• Founder is wildly painful and, for horses not euthanized, can create years of problems and pain. Foundered horses may struggle with frequent abscesses, tenderness, and imbalances. While osteoarthritis doesn’t link directly to laminitis, the damage from laminitis can undoubtedly contribute to joint problems.

Liver disease

• If your horse has eaten any black walnut hulls, their liver is at risk. The liver filters toxins invading the body, and mycotoxins from eating hulls, compound leaves, or bark can damage the liver.

• You will see a yellow hue in the whites of your horse’s eyes, and sometimes the gums will become yellowish, too.

• Liver damage is dangerous but can be helped with early intervention, medications, and a healthy diet, ideally created by an equine nutritionist.

Treatment of Black Walnut Toxicity in Horses

• First and foremost, if you find your horse in any hoof pain or colic situation, call your vet. If there’s more than one horse on the same type of shavings with similar signs, you have a big clue that black walnut toxicosis may be the culprit.

• After talking to your vet, remove the shavings or move your horse if possible. Severe pain may prevent your horse from staying put as you shovel the shavings.

• You may also need to wash (with soap) the lower legs to remove any toxins from the skin. The effects of skin contact may still linger even after the shavings are gone.

• Therapies like mineral oil and anti-spasmodic medications can help treat any colic happening at the same time.

Pain relief and ice therapy

• You and your veterinarian must manage your horse’s pain, usually with NSAIDs such as flunixin meglumine or phenylbutazone. Calcium channel blockers may be helpful in some cases.

• Pain relief can also happen with deep bedding over soft mats or soft, squishy hoof boots. If your shavings stores are questionable, use alternatives like coconut, cardboard, peat moss, or rice hulls if you have them. Most tack and feed stores carry alternative shavings and wood shavings.

• Icing hooves provides two things: pain relief and swelling ease. Most horses will stand in ice boots or buckets well, and talk to your vet about icing the lower legs. This cools the blood entering the hooves and may help with lower leg inflammation.

Hoof support from your farrier

• Your farrier and vet should work together to find the best trim and shoeing option during laminitis. This might include no trimming or pulling existing shoes in the acute phases of this disease and using soft, squishy boots instead.

• X-rays of the hooves help your farrier and vet find the best trim angles, and what type of shoe (if any) is best. Pour-in pads, leather pads, packing materials, and many different types of horseshoes are options.

No horse owner wants to see their horse in pain from laminitis, and knowing the source of your horse’s bedding is one way to prevent it. 

Frequently Asked Questions

What immediate steps do you take when a horse is exposed to black walnut shavings?

First, call your vet to get them heading your way. Then, you can remove all existing shavings. Keep your horse on soft ground, and wash their legs to remove any shavings dust and residue. Check on the other horses, too.

Can black walnut exposure be fatal to horses?

Yes, if exposure is prolonged. Or, a case of laminitis and founder becomes unmanageable and too painful, resulting in euthanasia. Even tiny amounts of bark, pollen, or shavings can harm a horse by ingestion, touching, or eating.

Video

Key Highlights

• Black walnut trees, commonly found in North America, pose significant toxic risks to horses due to compounds like juglone and mycotoxins.
• Exposure to black walnut shavings in horse bedding can lead to severe laminitis and related symptoms such as warm hooves and digital pulse elevation.
• Even minimal levels (5-20%) of black walnut in bedding can cause toxicity, highlighting the importance of careful material selection.
• Horses can also be affected by fallen branches, pollen, or walnuts in pastures.
• Removing black walnut sources and seeking timely veterinary intervention are crucial for recovery and prevention.

Citations

Martinson, K., Hovda, I., Murphy, M., & Weicherding, P. (2021). Black walnut: A toxic horse bedding (Publication No. 1320810). University of Minnesota Extension.

Skelly, C. 2020. Can my ponies be under a black walnut tree for shade? Extension Horses Knowledge Base, no. 662066.

Belknap J. K. (2010). Black walnut extract: an inflammatory model. The Veterinary clinics of North America. Equine practice, 26(1), 95–101. https://doi.org/10.1016/j.cveq.2009.12.007