- Wild horses running free; they're a romantic symbol of the American West, but the reality is that, today, there are far too many of them and they're caught in a battle between the government, environmentalists, and ranchers.

- So how did this ecosystem get so out of balance?

In part, it's because of a law passed nearly 50 years ago that was inspired by a young boy's dream to see these untamed creatures roam free.

(dramatic guitar music) Today, in parts of the country where herds of wild horses still roam, there is a curious yearly ritual.

(metallic clinking) Anywhere the Bureau of Land Management decides wild horses are overpopulating public lands, it sends in the helicopters.

Like flying sheepdogs, the aircraft chase bands of horses out of the hills, herding them, coaxing them, scaring them into a funnel-shaped corral.

Whether the roundups happen in the heat or in the snow, they follow the same pattern, and they end when cowboys on the ground release what's called a Judas horse, a domestic animal trained to lead its wild disciples into captivity.

Watching the drama from the sidelines are contenders in a high plains standoff.

- If it was just a little bit warmer that would-- - [Narrator] Wild horse advocates, like filmmaker, Ginger Kathrens, are against the culling of the herds.

- It doesn't happen very often, but on occasion, a horse might come in, it might slip on the ice.

- [Narrator] Sometimes, she confronts the BLM directly.

- We wanna go on record as saying that we don't think that this roundup ought to start today.

We think it's too dangerous, too cold, and too risky.

Helicopter roundups are incredibly stressful on the animals.

Foals will sometimes literally have their hooves fall off their feet.

- [Narrator] On the other side, ranchers paying to graze sheep and cows on public lands.

They say unchecked mustangs are damaging the range, eating grass that ought to be feeding domestic stock.

- I have a place in my heart for the wild horse, but there would be a lot of us out of business if we didn't have public lands to graze on.

(helicopter whirring) (hooves clopping) - [Narrator] So how did this situation get so tense, that the federal government is sending in herders and helicopters to mediate this standoff?

It's a classic tale of unintended consequences.

In 1970, the wild horse population had fallen from approximately a million at the turn of the century to less than 18,000, victim of a pet food industry hungry for cheap meat.

- Get that horse!

(tense orchestra music) (hooves clopping) (cowboy yells) - [Narrator] The 1961 movie, "The Misfits", dramatize the brutality of capturing wild horses, a practice which enraged a growing number of animal lovers.

- [Woman] Killer!

Murderer!

(hooves clopping) - The mustang, maybe more than any other animal in America, is a symbol.

It means freedom, it means defiance, it means scrappy, but noble.

In a sense, it means us, right?

It is the American.

And to have something that we hold in such a steam at the same time, not only abused, but turned into dog food, was just something that people could not deal with in their minds.

(horse neighs) - Knowing that animals were being hunted down, slaughtered, butchered, and sold as pet food just really burned me up.

- [Narrator] Greg Gude was a young boy when he discovered the plight of the mustang in the pages of an illustrated children's book.

Its main character was the tenacious Nevada activist with a catchy nick name.

- [Announcer] Velma Johnston has fought for the protection of these animals all her life and she is known as Wild Horse Annie.

- [Narrator] Wild Horse Annie enlisted school children in a national letter writing campaign.

By some accounts, they flooded congress that year with a volume of letters second only to mail received about the Vietnam War, but Greg Gude didn't need to write letters.

His Father, Gilbert Gude, held one of Maryland's seats in the U.S. House of Representatives.

- I lived with my Congressman.

I could lobby at the dinner table.

I think it probably took a hunger strike.

- An 11-year-old boy persuaded his father, a congressman, to introduce a bill to protect wild horses and burros on the Western Plains.

Then the boy, Greg Gude of Maryland, appeared today to testify.

- [Narrator] And so, a few months later, in December of 1971, the wild horses were saved.

- Today, President Nixon signed a bill to make killing them a federal crime.

- [Narrator] This largely halted the commercial capture and slaughter of wild horses roaming the west, but it wasn't long before mustangs were making news again.

- It may surprise you to hear there's a surplus of wild horses in what was once the Wild West.

- Soon as the law passed, there were essentially more horses than the government knew what to do with.

There's only a certain amount of grass out there, especially in the West, and most of it's already spoken for.

- [Narrator] Ranchers who rely on public lands for their live stock say what's at stake is their claim on the American West.

- I roped my first wild horse when I was 11.

That was in 1952.

There are people that think the wild horse is a symbol of the American West.

I think every rancher will tell ya that we're riding the horses that built the American West.

- [Narrator] Garrett says activists have browbeaten the BLM into culling too few mustangs.

- Yesterday, they-- - Horse activists, like Ginger Kathrens, see it differently.

- If you're wondering why our public lands are overgrazed or degraded, you need to look at the millions of head of livestock, cattle and sheep, that are permitted to graze out here.

- If you talk to advocates, spend some time at a roundup with them, eventually they'll talk about how the BLM is in the pocket of big ranchers.

And if you talk to the ranchers, (chuckles) if you spend any time at their ranches, they will talk to you about how the BLM's in the pocket of the advocates.

- [Narrator] BLM removes approximately 4,000 horses a year, hoping to find them permanent homes, but periodic exposes over the years reveal that the animals sometimes met a different fate.

- NBC News has been told by just about everyone we talked with a large number of BLM horses likely end up slaughtered.

- BLM sort of binges and purges when it comes to horses.

They'll ignore the problem of overpopulation until it gets really bad and then, they'll do something they regret.

So in the '80s, they sold a bunch of horses to people that then slaughtered them.

And in the '90s, they started doing the same thing again.

They would sort of do a don't ask, don't tell type of thing, where we're gonna sell you the horses.

Don't slaughter them.

We're just never going to check.

- [Narrator] The BLM insists it does not knowingly sell horses to so-called kill buyers.

And today, the growing number of horses and the fewer people willing to adopt them have given rise to what may be the biggest unintended consequence of the 1971 law.

- The Bureau of Land Management is probably the largest horse owner in the continental United States, maybe the world.

- [Narrator] There are more than 46,000 formally wild horses and burros living in corrals and long-term holding pastures in the Midwest, eating grass on the government dole.

The BLM spends almost $50 million a year to board these captured animals.

The Government Accountability Office has warned the ballooning holding costs will overwhelm the program.

- I mean, we're talking 40%, 50%, 60% of our budget is going to the holding and caring of animals.

We're full up, there's no where to go.

There's no where to go with them.

I really don't know what to say other than it's not sustainable.

- [Narrator] The BLM estimates the number of wild horses on federal range lands could soon exceed 100,000.

Drastic measures, like euthanasia, provoke a strong public outcry, so the agency treats some horses with birth control and recently added a new program, offering up to $1,000 to anyone who adopts adopts a wild horse.

- It's unclear what is gonna happen when they no longer have the money to expand the system.

Do they leave horses on the range and get sued?

Do they sell horses to the market and have them slaughtered?

Do they euthanize them in some massive, crazy process and just bury them in a big pit?

Seriously, when they run out of money, what happens?

- It's a problem and not an easy one to solve.

- They really made a mess of it.

Are they wild horses when they are in captivity?

- It's awful.

We have to manage wild horses on the range.

- I don't think anybody likes it, but nobody can find a way out of it.

The law really did save the wild horse.

The question is, what do we do with the wild horses we saved?

(hooves clopping) (dramatic music) (calm music)