I did look at the photos, and yes, you're right, Fudge is a little ribby and not in as good condition as the rest of the herd. He's also very cute! Honestly, though, my advice is still the same. You've eliminated bullying and the other horses stealing his food. Put him on an agressive worming schedule, get the vet to check his teeth and increase his food. Since the other ponies seem to be thriving, I'd try giving Fudge some high quality concentrate (sweet feed, pellets or the like) on his own. If all that fails, get the vet to draw blood work.
Hey Maura, I've posted something else on the malnutrition! It would be great if you could take a look! :)
Thanks again, Molly!
(thats my name cause i think its really longwinded when you have to call people there name like, XxFUDGEISTHEBOMBxX!!!)