A very strong caution
If you find yourself having to dry lot a horse, you must make a careful survey of the plants and trees your animal may be able to reach.
Horses in dry lots will eat things that horses in large pastures will likely leave alone. (Foals may or may not leave them alone since they explore with their mouths)
You may think you are keeping slow feed hay in the lot at all times, but almost always your horse will have time periods where it runs out.
When that happens they Will start looking for things to do.
Red maple tree leaves, bushes, Walnut trees (include the bark), Azalea, and various other plants and trees will all become targets for your horse’s mouth.
These types of plants can lead to death, severe colic, laminitis or neurological issues.
Make sure you use a plant identifier app and look up the things your horse may be able to reach.
Be aware, when they are bored they develop giraffe necks and can reach much further than you’d think.