Check it carefully. Is there any sore or swelling there? Is that black part bothering your dog? Have you observed any other symptom in your dog that is unusual? If there is a sore that is not bothering your dog then there is no need to get worried. But if it is making your dog panicked or bothering it somehow then you need to have its test. Biopsy is the test to ensure that your dog is not having a disease like cancer. But if test results will not come according to your desire or wish then your dog will have to under go chemotherapy or radiation in order to get rid of tumor or cancer. Take it to vet soon. Later thing is not connected with the prior problem. Second problem is digestion problem. Feed it light diet.
