Metacam would be ok, but rin your vet first if you really feel he should have it, also the dose is tiny, literaly a drop, my old piggy was on it long term. He will be sorry for himself for the next few days, but it's understandable. He will be sore! Like everyone else has said, keep him warm and make sure he's eating. A lot of the time when they feel unwell they wont do anything if they are being watched by our beady human eyes!