It’s a stupid law that doesn’t allow them to be slaughtered anyway.
Problem was, when they made horse slaughter illegal, it didn’t stop killer buyers from buying them and shipping them to Mexico and Canada. I don’t know how the Canadian slaughter system works but the one in Mexico is horrific. The U.S. slaughter plants were much more humane. Also, the horses usually didn’t have to travel so far in stuffed tractor trailers. Fortunately, the double decker tractor trailers can’t haul horses, which is illegal.
There is still a horse slaughter plant open in Texas. Dallas Crown, in Kaufman, is still in operation. Although I think they only slaughter horses for the zoo market.