Quantity
There's no established safe amount, but the toxic dose appears to be roughly 50% or more of the diet for several days. The problem is that horses grazing in oak-heavy paddocks can easily reach that threshold without you realizing it. Even smaller quantities eaten consistently over a week or two can cause cumulative kidney damage.
Notes
Autumn is peak danger season when acorns fall, but green acorns and young oak leaves in spring are also toxic. Some horses develop a taste for acorns and will actively seek them out, almost like an addiction. All oak species produce toxic acorns, though the tannin concentration varies. Ponies and young horses seem to be more susceptible. Wet years with heavy acorn crops are especially risky — fencing off oak trees during acorn drop is the single best prevention.
Negative Signs
* Loss of appetite and depression — your horse goes quiet
* Dark, tarry, or bloody diarrhea
* Increased drinking and frequent urination (early kidney damage)
* Decreased urination or none at all (kidneys shutting down)
* Colic signs: pawing, looking at flanks, restlessness
* Edema — swelling under the belly or in the legs
* Weakness and reluctance to move
FAQ
Q: I found acorns scattered in my horse's paddock. How worried should I be?
A: Worried enough to act. Fence off the area under the oak trees if you can, or move your horse to a different paddock during acorn season. Check for signs of acorn consumption — green-stained muzzle, chewed acorn shells in the manure. If your horse has been eating them, get a vet out for a blood panel to check kidney values.
Q: My horse has grazed near oak trees for years with no issues. Is it suddenly going to be a problem?
A: Possibly. Some years produce heavier acorn crops than others, and some horses develop a sudden taste for them. Past tolerance doesn't guarantee future safety, especially in a heavy acorn year.
Alternatives
Make sure your horse has plenty of good-quality hay and forage available during acorn season. A horse with a full belly is far less likely to browse on acorns. Fencing off oak trees or picking up fallen acorns daily are the most reliable prevention strategies.
Risks & Disclaimer
If your horse has been grazing near oak trees and shows any of these signs, call your vet immediately. Kidney damage from acorn poisoning can be irreversible. Bring your vet information about how many oak trees are in or near the pasture, how long your horse has had access, and whether you've noticed acorns on the ground.
