That looks like classic ringworm. Ringworm is a fungus highly contagious but it will run its course without treatment. I have heard it called rain rot as well. In our part of the country we get it this time of year when it has been really wet.
Ringworm (barn itch, dermatophytosis) is the most common skin infection of cattle and is caused by a spore forming fungus called Trichophyton. Spores can remain viable for months in the soil or bedding and for years on objects such as halters, grooming equipment, working facilities, and barn surfaces. Cows become infected by simple contact with dormant spores from objects or other infected cattle. Upon germination the fungus invades hair shafts and superficial layers of skin. Body fluid exudes from the damaged skin and mixes with dead tissue to produce the classic tan or gray elevated crusty scab. These lesions are generally circular or oval in shape but they may coalesce to produce large irregular patches. Ringworm is usually found on the head, neck and trunk of calves, particularly around the eyes, ears, and muzzle. Unthrifty animals and those with compromised immune systems tend to be much more severely effected than healthy calves. Winter housing, confinement, and crowding are more conductive to an outbreak than summer pasture. This is a self limiting disease in that animals develop immunity to the fungus and the infection usually resolves in 2 – 6 months without treatment. It is uncommon to see ringworm in adult cattle, especially if they were infected as calves, but sporadic cases do occur
gizmom
