Veterinary researchers identified oak toxicosis as the cause of severe kidney failure in a cow and death in a bull from the same herd and examined at Auburn University. Cattle and sheep are vulnerable. Once ingested, oak tannins break down to gallic acid and pyrogallol in the rumen, damaging renal tubules and blood vessel linings.
Signs of oak toxicosis include anorexia, dehydration, rumen stasis, constipation and bloody diarrhea. The case was reported in the Journal of the AVMA.
Source: Vet Candy, September 29, 2026. Link. The problem lies in tannins. Some species produce salivary proteins that bind tannins and keep them from being converted into toxic byproducts. Cattle have fewer of these proteins, and those they have bind less effectively.
Leaves, buds, and acorns can all be toxic, but timing matters. Young leaves and buds are most dangerous in spring, and their toxicity fades as the foliage matures. Acorns take over as the bigger threat in the fall.
Image: Link.
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