Hooves can be very dangerous. I don't mean to alarm you, but they can cause serious problems if ingested whole, or in large pieces. Even small pieces can splinter and pierce the intestines. I would get your dog to the vet as soon as you can.

Hooves can also chip a dog's teeth, because they are so hard. My dog, Keito, had to have a filling put in one of his canine teeth because one of my friends gave him a hoof to chew, and it chipped his tooth ... that ended up being a $150 hoof!

I don't give my dogs hooves to chew at all, and I only give them rawhide with strict supervision.