My horse has been showing signs of soreness as well on hard frozen ground and my farrier said that most horses will feel tender on the frozen ground especially if they are barefoot. My horse will canter on the soft snow and no pain anywhere else so I’d have to agree with him. On cold hard days he’s slow and tender, when it’s soft he’s ok, so I’m just giving him a break on the icy hard ground days, and I’m getting him a pair of the hoof boots from Calvelo? they sell that on smartpak or at the cavelo website.
I wouldn’t rush right to radiating his legs. =) good luck.