When a previous horse of mine foundered, He stopped moving, continued to eat, but couldn't move - it looked as if he was having extreme difficulties putting weight on his front feet, and refused to walk on hard or rock covered ground. Both the farrier and the vet confirmed that he had foundered, and luckily we acted quick enough and got a treatment plan worked out. If you suspect your horse is foundering, I would call either a vet or a farrier.
Do there hoof show a difference? I don't think he has it but I just never knew much about it. I had owned a horse who had foundered previously before I owned him. How would a farrier tell by just looking at his feet?
If you visit my barn and look at the horse Faith, she was severely foundered when I got her, there was a video of her,but the "rescue" removed it from youtube, but I have pics of her xrays and a picture of her hoof here is the link http://www.horseforum.com/horses.php?horse=7627
The feet will be hot, and you will able to feel pulses (talk to your vet or farrier about how to feel for these). The horse will also take a stance with their front legs far out infront of them to reduce pressure on the painful areas of their front feet. In less advanced cases the horse will only be lame infront, however the pulses will always be there (these are the best indicator).
Immediately call the vet, bute the horse, get him standing in ice water or cold hose and standing on soft surfaces and/or tape thick styrofoam to the bottom of his hooves after icing them.