There are about 48,000 wild horses on our grassy Western plains, which is nearly twice as many as the range can support, according federal wildlife managers. Obviously, the range is currently supporting all those horses, so talk about how many horses the range can support is an oblique way of talking about competing calls on that range. And the most obvious competitors--or at least the most vocal--are ranchers, who don't like all those horses eating grass and drinking water that could be going to their cattle.
What definitely seems unsustainable is our current wild-horse policy. Since 1971 it's been illegal to capture or kill wild horses. So to keep numbers down, the Bureau of Land Management has been rounding up wild horses and storing them in feedlots and fenced pastures. The Bureau is now responsible for some 50,000 warehoused wild horses, which it can't euthanize or slaughter. The horses can be adopted, but adoptions have never kept up with removals, just as there have never been enough removals to keep the wild population to a "sustainable" number. The Bureau currently spends $50 million a year on its horse hotels, which leaves too little money for additional roundups.
I learned all this from a New York Times article, the most interesting feature of which was the startling omission of two words: invasive species. Horses are not native to the New World. The wild horses of the American West are the feral descendants of domesticated horses brought over by the mainly Spanish early settlers. Like many other immigrants to our shores, the horses found America a great place to settle down and raise a family.
People pretend to object to invasive species, but that only applies to species they don't like. Everyone has a fondness for horses, so attempts to wipe out these four-legged invaders are not in prospect. Indeed, we tend to pass over the uncomfortable fact that they are invaders; the Times article noted that unchecked horse populations could decimate grass and water on public lands, potentially leading to "starvation among horse herds and other native species" (my italics). You're in, guys!