I once had a Persian cat who had a deficient immune system and had chronic ringworm. We tried everything on him including a couple of strong fungicide prescriptions from the vet that were pills we gave him. Nothing seemed to work for more than a month or so. I hated giving him those pills every few months because they are toxic when used extensively. I bathed him in cat shampoo, to which I added tea tree oil and grapefruit seed extract. I'd leave it on for about 5 minutes and then rinse it off. This seemed to give him some relief.
WE use it in thier shampoo and have an oil mixture of Tea Tree, PennyRoyal, and grapeseed oil.
It has helped thier coats. I wouldn't use this recipe during flushing, estrus, or during pregnancy because of the PennyRoyal, but you can while milking, just be sure not to get any on the udders. We brush some on very lightly over coat then use a papertowel around the polls to get in deep.