U.S. Constitution: Tenth Amendment
The powers not delegated to the United States by the Constitution, nor prohibited by it to the States, are reserved to the States respectively, or to the people.
The question becomes if it does in this situation. This situation has a little more to do with Interstate commerce than a lot of situations do so I might have to give that Federal law might trump here. My opinion don't matter though, it's the judges opinion that counts.
Now a personal note on this. I would not personally want to eat horse meat but if that's what someone else wants to do that's fine. It's a mammal just like a cow so if you protest eating horses you should also protest eating a cow. If you don't like horse slaughter don't pass laws against it. Spend your money buying horses and feeding them until they die.
A horse is dangerous at both ends and uncomfortable in the middle. Ian Fleming
