Ox Horns

Can you post a picture of it so we have a better idea of what the problem is? I could be a number of things.

It is hard to tell in the picture but it does not look like a fracture that goes all the way through the shell of the horn and into the soft tissue. I doubt if it is related to nutrition, probably from rubbing it on something. The horn material is layered and if you crack a surface layer it can tend to delaminate a little bit. It will not re-attach or grow back together but you can try filing it down a little with a file so it is not as noticable. You did not say where you are or what they were eating over the winter but I would tend to feed a steer that age a diet with 12% to 14% crude protein so if you had average grass hay a little grain with soybean meal would bump up the protein, and a mineral supplement would be good. If they are on good pasture now there should be no need for a protein supplement.

I tried to look at it a gain by expanding the picture and it looks like more chips and mechanical damage on the top of the horn. I think he is rubbing it on something, maybe the fence or something metal. Sometimes they will scratch their horns and poll if they have fleas or lice so make sure that is not the case. I would just start working over the horns lightly with a file once a week or so to smooth them off. Some animals just rub them a lot harder than others.