Pretty sure it must be an abcess. The bute worked and he was sound this morning but back to very sore to night. Abcess lameness is just *different* and there's just the hint of warmth (just where he chipped a chunk of hoof off last month!!) so I'm hoping it is. No swelling anywhere, no tightness when we did the shoulder exercises. So tomorrow it's the vet and his knife, probably, and hopefully not too painful for my baby.