As long as the Republicans control Congress, I don't know how likely it is this legislation will pass because their first loyalty is to Big Business (as I'm sure Cajun is aware of and supports, since she is a loyal Republican-- though we're on different sides of the political fence, Caj, I LOVE that there's another female on the board who cheerfully voices her political opinions-- you can always keep them coming with me-- I never take a political argument personally).
That said, I don't know that this law would pass with Dems in charge-- they tend to be more progressive, but it opens up a big can of worms in terms of some animals being "more equal than others," to borrow from George Orwell. Fact is, any of us who eat factory farm meat (which is virtually all of it) are contributing to enormous amounts of animal cruelty. Directly, with our spending money.
So, in the meantime, send your some of your spending money to horse rescue operations. If you can't rescue 'em all yourselves, then at least send what you can to those places that try to. If you're not willing to back up your convictions with your money in a capitalistic society, then nothing will happen.
And then write your Congressman.