Dry powder with mineral additive has been used, but it is a slow process to clear these up. Avoid fly contamination and other foreign material. Check with a dairy veterinarian in your area.

Mike Hutjens, Extension Dairy Specialist, University of Illinois - Illini DairyNET

The cause of udder sores, sometimes called udder necrosis, especially in the fore udder, has been reported as Chorioptic mange caused by Chorioptes bovis, the parasitic worm Stephanofilaria, and simply pressure and rubbing. Chorioptic mange can also be on the tailhead and other places where skin rubs together, such as inside the rear legs. Treatments described and advertised include various ointments and gels. Antiparastic therapy such as ivermectin is not often described as a treatment. However, experience and most recent expert advice suggest that cleaning the sores (usually the easiest way to do this is with a cloth towel) followed by application of a dry powder, usually including talcum, is the best therapy. On some cows, the sores are very frustrating and hard to clear up. They can smell bad enough to make milking unpleasant.

Dave Wilson, Dairy Extension Veterinarian, Utah State University