Hock burns are lesions found on the hock joints of chickens and other birds raised on broiler farms. They are considered a form of contact dermatitis. These marks occur when the ammonia from the waste of other birds burns through the skin of the leg, leaving a brown ulcer mark. The condition has been found to be a source of pain for birds, can cause mobility issues, and may increase the risk of bacterial diseases. In severe cases, hock burns can cause visible scabs to form.