Join Date: Nov 2011
Location: Central Oregon, USA
This is a very debatable topic.
Are we talking just for movement, to have grazing, to have supplemental grazing vs enough grazing to sustain a horse without hay?
Is this arid land, land with rainfall, does the rainfall come in the growing season, is irrigation available? Is there TOO much water making the soils hydric and growing less palatable hydrophytic plants?
If it is just for movement and exercise, not including grazing, I like to see 1-2 acres per horse total. This leaves room for shelter, compost/manure management et cetera.
For grazing, that is super variable. Irrigated (naturally or via sprinklers or flood irrigation) pastures require a lot of maintenance to keep them nice, but you can get away with 1-3 acres per horse is rotated and not overgrazed.
In my neck of the woods, without irrigation and only 9 inches of precip per year, a horse would need about 500-1000 acres to survive without hay. Not practical.