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"Poisonous" does not mean deadly. Some manifestations of toxicity are subtle. The dose, as always, determines if a plant is safe source of nutrients or a toxic hazard.

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BRIEF: Are acorns poisonous to horses?

I have a friend whose horses are eating "acorns". I have never run into this before. It has been more than 72 hours since she noticed this and there have been no obvious symptoms of sickness. Acorns are not listed as a problem to horses. Is this particularly bad for them? In their pasture, it will be hard to control. Do you think any problem will result from this?


It depends on the species of oak, how much they are eating and what else they have to eat. If they have little else to eat, the acorns are from a high-tannin variety and they are eating pounds of them, then protein deficiency at least and severe tannin/polyphenolic toxicity at worst may ensue. If the horses are on full feed, have an otherwise balanced diet and are just nibbling the occasional white oak acorn, no harm done.