It's a fungus, usually looks like a sgreyish splotch. High contagious from animal to animal and animal to people. Frequently places that an animal has been that has it will also contaminate others with it.
We had lots of rain mid-summer and our cows had it. (I got a little spot of it, too. ) It started out looking like whelps on the cows and calves, but you could feel they were scaly beneath the hair coat. Cows are fine now. They will scratch it, but ours didn't get as bloody as I was afraid they might.
Use athlete's foot antifungal if you get it. I washed my hands fanatically and still somehow ended up with it. Itched a little, but not too bad.