We've been battling ringworm on 5 calves that we are getting ready for the Classic. Noticed it the week before Christmas and didn't get a good start until the week after Christmas. It was pretty bad by then.
We've used a combination of Scarlex and Blue Star Ointment. The Scarlex is made for open wounds on horses, but it has worked good for us. It is anti-fungal (ringworm is a fungus), antibacterial, and it is an oil base so it doesn't dry out. It comes in an aerosol spray can for $6. The Blue Star Ointment came highly recommended on this site, so we've been trying that too. We have one calf that goes nuts when we use an aerosol spray, so spreading the ointment using my finger works great. As stated many times on this site, it is very contageous so use rubber or latex gloves to keep you from getting it.
We worked our calves hard for one week and I've noticed hair growing back in. The recent cold spell has limited our time with them recently. I'm prepared to start using the MTG as previously noted to help regrow hair. Some of our spots were as big as the palm of your hand.