Thanks everyone for your feedback. We did call the vet right away when we first noticed the cut. He said to put fly powder on it and just watch it. So when we noticed it spreading we called the vet again. Again we were told just to watch it. The cow is otherwise healthy, she eats fine and doesn't seem to be in any pain. We don't believe it to be anything contagious, as the rest of our herd is fine. We are now waiting for the vet to come and check her out. The area now has a hard scab over it. I'll let you know what the vet says.