Because of the way dogs lie and put pressure on their elbows, the fur rubs off and callus forms. Calluses actually protect the area as they become thick and hard. Providing a well-cushioned bed helps relieve the pressure, although some dogs prefer to sleep on hard surfaces. Unless the area appears to be infected or inflamed, a vet visit isn't necessary. Make sure the area is cleaned well. There are products on the market that can help soothe the callused elbows. You can also rub in vaseline or vitamin E oil a couple of times a day. You have to keep an eye on the bleeding so that the area doesn't become infected. If the problem continues then it's time for your pup to see the vet.