The West is on the verge of a serious horse crisis. That's the upshot of a new paper in Science, which argues that the wild horse population is growing so fast that the government could soon be unable to manage the herds.

Wild horses run as they are gathered up by BLM near Tooele, Utah. (Jim Urquhart / Reuters)

Here's the back-story: There are currently an estimated 33,000 wild horses roaming freely on public lands in the western United States, descendants of horses brought by Spanish conquistadors. Under a 1971 law, the Bureau of Land Management is supposed to protect these horses and make sure their numbers don't get out of hand — so that they're not destroying the ecosystem or dying of starvation.

But that's easier said than done, and BLM has long struggled to bring the horse population down to what it deems the "appropriate management level" of around 23,622. There are, after all, only a few thousand people willing to adopt horses each year. And Congress has largely restricted the slaughter of healthy horses.

So, in recent years, BLM has been rounding up excess horses and shipping them off to long-term "retirement" facilities — mainly private ranches in Kansas and Oklahoma. The problem is that this is hugely expensive: There are now 45,000 horses in these facilities, and BLM's horse budget has soared from $19.8 million in 2000 to $74.9 million in 2012.

Lately, Congress has started reining in spending here. BLM has announced that it will remove fewer horses from public lands this year. At the same time, the wild horses keep breeding, with unmanaged herds able to triple in size in just six to eight years.

See here for more detail.

Put it all together, and it's a big problem in the making.

The Science paper, written by Robert A. Garrott of Montana State University and Madan K. Oli of the University of Florida, calculates that if current trends continue, BLM would have to spend some $1.1 billion over the next 17 years just to keep storing horses in these long-term facilities — a level far beyond anything Congress seems willing to contemplate. (See chart.)

And if round-ups are no longer an option, then the number of wild horses on U.S. public lands could start swelling — dramatically. "The worry is we'll end up like Australia," says Garrott. Out in Australia, the wild horse population has soared past 400,000, and the government is now reportedly considering shooting tens of thousands of horses in the outback, both to stop the destruction of range land and to alleviate the suffering of horses that have been slowly dying of thirst during a recent drought.

"Some horse advocates have argued that we should just let the horses self-regulate on public lands," Garrott says. "But what do we do when animals are destroying rangeland, competing with livestock and other wildlife and dying due to starvation and drought? That's not good for the horses, it's not good for the range, it's not good for anyone." He notes that BLM has already been straining to deliver water to horses in Utah and Nevada during this summer's drought.

In their paper, Garrott and Oli argue that it's long past time to get America's horse issues under control. That would start with an aggressive vaccine contraceptives program to cut the birthrates of the wild horses by half (that won't be cheap, since the horses need to be rounded up every few years). But contraception by itself, they note, is insufficient. BLM would also likely need to remove many of the existing wild horses from public lands to bring the base population down to around 23,000 or so.

Getting those numbers down is the hardest part, and the paper doesn't take a stance on how best to do this. Congress could, in theory, appropriate many more millions of dollars to have BLM store even more wild horses in long-term pastures. Or the government could cut back on livestock grazing in order to give the horses more room on public lands.*

Another option that gets touched on — and this one is far more gruesome — would be for the government to kill off thousands of healthy horses to bring the numbers down. Horse slaughter is subject to a huge amount of controversy, and horse-meat plants have been closed ever since Congress pulled funding for inspectors in 2007. (Lawmakers have since reinstated those funds, but the reopening of slaughterhouses has still been bogged down by legal disputes.) Needless to say, this idea would encounter fierce opposition.

Yet whatever the method, the Science paper argues, if Congress and BLM could figure out how to get the number of wild horses down to around 23,000 or so, then contraceptives plus adoptions could keep the population at a sustainable level, for good. And that would mean no more slaughter. No more spiraling costs. And, most significantly, the West's horses would avoid the painful fate of their Australian counterparts.

It's just that getting to that sustainable level has proved incredibly difficult over the years. "We think this can be resolved," Garrott says. "But it's going to take a real forward-looking plan."

* Update: Here's an additional point from the American Wild Horse Preservation Center. Using BLM figures, the center estimated that about 82.5 percent of the forage in wild horse herd management areas is actually reserved for livestock grazing, while just 17.5 percent of the forage is allocated to the horses themselves. So BLM could alleviate overcrowding by scaling back livestock grazing on public lands. That's likely to be controversial among ranchers, but it's worth noting here.

Related: For those who can't access the Science piece, the National Research Council came out with a big study on BLM's wild horse program earlier this year.