My horse provides about a hundred pounds of manure a day, and my trees and grass give me mor good additions to compost. My garden will be okay and I’ll be able to feed myself. But the whole world can’t do that.
I used to have horses, but they & their manure are long gone. Aged horse manure is great stuff. I do have access to small amounts of chicken manure, but haven’t used it yet - it’s an option.