If he's got wounds on them then let them heel up first. I've used this a couple times and did what the jar told me I had to give my strike about a week or two off until he got back to running as fast as he could but this worked. I kept putting In on twice a day for about week even after he got better.
http://www.hyperdrug.co.uk/Pad-Hardener-100g/productinfo/PADH/