The American west is being overrun by wild horses

America has way, way too many horses, according to a new study published in Science, and it could cost U.S. taxpayers $1.1 billion over the next 17 years.

There are about 33,000 wild horses running free in the United States. Descended from animals brought over by the Spanish in the 1500s, they roam throughout public lands in western states like Colorado, Nevada, Wyoming, and Montana.

Overpopulation is a big concern. Too many horses could result in rangelands being stripped bare and an eventual population crash, which is why the Bureau of Land Management (BLM) has a mandate to keep the number of wild horses at 23,622.

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When wild pig or deer populations get out of control, the solution is simple: Allow hunters to kill them. With horses, it's not that easy.

While horse meat is regularly eaten in France, Sweden, and Japan, it's taboo in the United States, as well as in England, where ground horse found in supermarket hamburgers caused a minor uproar earlier this year.

The USDA has no inspectors to deal with horses. That means to cull the population, a government official would have to sign off on shipping thousands of horses down to slaughterhouses in Mexico — not a move that would win any popularity contests with the American public. (There is, however, a movement afoot to reopen a small number of strictly regulated domestic slaughterhouses to deal with the horse problem.)

Wild horses can also be adopted. Unless, however, there is a serious spike in wealthy homeowners with room to spare, adoption isn't likely to make a serious dent in the number of free-roaming horses.

That has left the government with one option: Rounding up horses and sending them to private ranches, which cost the government $74.9 million in 2012, according to The Washington Post. By 2030, the new study says, the U.S. government will have spent $1.1 billion providing food and shelter to wild horses.

Around 45,000 horses are kept in these "retirement" ranches — and their numbers could increase dramatically in the future. That is because the wild horse population has been growing at a rate of 15 to 20 percent each year, putting more pressure on the government to find places to put them.

There is no easy solution to the problem, though advances have been made in the field of horse birth control, most recently with a liquid vaccine that needs to be injected once a year.

Still, rounding up thousands of horses, injecting them with a vaccine, and tracking their progress is a daunting administrative task. The BLM says it has vaccinated 4,562 wild mares since 2005, "but significant reductions in the rate of population increase have not yet been apparent."

Eventually, the United States could find itself in a similar situation to Australia, who is now so desperate to reduce its population of 400,000 wild horses that it's considering shooting tens of thousand of them.

"We need to think about what's ethical, what we want to do. The worst-case scenario is that we do nothing," Robert Garrott, co-author of the study, told the University of Florida. "Simply not doing anything will result in a much, much harder decision in the future."