Very small quantities of black walnut wood residue in shavings can cause laminitis in horses. As little as 10 percent of the total shavings, by weight, may result in clinical signs of toxicity in horses.
These signs generally occur within 24 to 48 hours of exposure to the contaminated shavings. The symptoms frequently begin with mild laminitis and swelling of the legs and can progress to extremely severe laminitis, swelling and edema of all four limbs; and pitting edema of the ventral abdomen; and colic.
Source: My Senior Horse, January 5, 2026. Link.
INSIGHTS: Purdue University has a downloadable PDF that can help horse owners avoid this issue when they are buying shavings for bedding. It is easy to print and share.