With evidence indicating that large grazers help us by indirectly keeping the Permafrost colder, wouldn't it be logical to attempt a mass relocation of mustang horses to Alaska and maybe parts of Northern Canada? It seems like a more viable solution to the 'wild horse's problem that also benefits us and the environment.
Alternatively, we could import Yakutian horses or the wild Pzrewalski's horse instead, but it seems like it would at least be worth a try.