America’s last remaining horse-processing plant closed September 21, 2007. The closure resulted from an Illinois State law(5) prohibiting horse slaughter for human consumption overseas. It was signed by Governor Rod Blagojevich.

Two plants in Texas were previously shuttered when the 5th Circuit Court of Appeals(6) reaffirmed that horse slaughter for human consumption is illegal in the state. 

Six states prohibit consumption of horse meat: California, Illinois, Mississippi, Oklahoma, Texas, and Florida. California was the first state to outlaw the processing of horses for human  consumption, putting horses under the same pet classification as dogs and cats. The State's voters approved Proposition 6(7) in 1998.

In 2006, the USDA reported 138,206(1) American horses were processed for meat, both for human consumption and to feed captive carnivores. Of those, 102,260 were sent to U.S. facilities, 24,866 to Canadian facilities, and 11,080 to Mexican facilities. 

The U.S. plant closures were hailed as victories by animal rights activists, who said horses would no longer be killed for human consumption. A high-quality, low-fat protein source, horse meat is eaten in Austria, Belgium, Canada, Chili, China, France, Germany, Iceland, Indonesia, Italy, Japan, Kazakhstan, Malta, Mongolia, The Netherlands, Norway, Poland, Slovenia, Sweden, Switzerland, and the United Kingdom.

Since the U.S.  plant closures, USDA figures show an increased number of American horses are being processed in foreign facilities. In 2008, close to 80,000 horses were shipped from the United States to Mexico. Approximately 40,000 went to Canada. The USDA's numbers are based on owner/shipper certificates corroborated with other sources. [Osborne 2009]

The well-intended legislation enacted to help horses has its critics. An historically-established segment of American industry was forced out of business, leaving horse owners with reduced sales opportunities. Horses being sent to foreign processing plants now face longer trips. And, since buyers must pay more for the extended trips--up to $200 per head--the market for lower classes of horses (mean, dangerous, excess, aged, infirmed, untrained) has plummeted.

The cost of keeping a horse has not. Exacerbated by a downturn in the U.S. economy, horse owners are facing a costly burden of maintaining animals they find difficult to support. Unfortunate horses are facing less-than-humane treatment. It is difficult, if not impossible, for people to sell animals they no longer want, need, or can afford. Indeed, it can be impossible to give a horse away, and then there is the concern about how the animal may be treated by the new owner.

Demand for services at horse rescue centers and sanctuaries(3) is up. Some established centers are reporting a ten-fold increase within the past year, and budgets are stretched to the breaking point. They are able to provide but a fraction of the care needed to address the current population, let alone the numbers of horses that will be added in successive years. Sadly, in a few instances, well-meaning horse rescuers are themselves being overwhelmed, with the horses they vowed to protect being starved yet again.

Across the United States, horses are being turned loose and left to fend for themselves. Some have had identifying brands cut from their hides to make tracing ownership impossible. Others are being found in corrals and stables without feed or water, the owners having walked away from the problem.

There are groups and individuals who believe horse slaughter is inhumane, that horses should be allowed to live out their natural lives regardless of age, infirmity, or illness. Some dispute the fact that there is an abandonment problem, contending the few cases there are result strictly from the downturn in the economy.

Those advocating for the option of processing unwanted horses in the United States--including many horsemen and horsewomen--feel neglect and abandonment are equally inhumane. They are sounding the alarm of a developing crisis involving the American equine industry. They believe the problem  is, first and foremost, caused by plant closures and made worse by the economy. 
 

Additional Reference:
Osborne, Malinda. 3/1/09. "Horse slaughter conditions in Mexico explored by AAEP group," JAVMA