Tens of thousands of horses were killed in 2012, as the economic crisis had owners abandoning the once prized status symbols.
The Spanish government said nearly 60,000 were slaughtered in abattoirs in 2012, a number twice those killed in 2008.
"A few years ago we were rescuing horses in isolated cases, ones that were mistreated or abandoned. Now the problem is happening in all sectors," Virginia Solera, who helps run a shelter for some of the abandoned horses, told Agence France Presse.
"In Spain, having a horse is a sign of wealth," she said. "A few years ago, before the crisis, a lot of people thought: I'll buy a big car, a big house and why not a horse?"
Maintaining a horse can cost up to 400 euros ($520) a month, but sending it to slaughter can yield 150 euros ($195).
More on GlobalPost: The beef with horsemeat
A horsemeat scandal has been spreading across Europe, with various meat suppliers and food chains finding horse DNA in their beef.
In the United States, horse slaughter may begin again after a 2006 ban lapsed in 2011. According to ABC News, industry pressure and a lawsuit forced the USDA to fund horsemeat inspectors again, allowing slaughter houses to reopen.
Sen. Mary Landrieu and Reps. Patrick Meehan and Jan Schakowsky are set to introduce a bill on Wednesday that would stop the horse slaughter.
The Safeguard American Food Exports Act would ban the slaughter of horses for food and also prohibit shipping them outside the country for consumption purposes.
"Horses sent to slaughter are often subject to appalling, brutal treatment," said Schakowsky, in a statement to ABC.