Thanks for the additional information. It is helpful.
There are usually only a few different reasons that a dog will chase their tail crying. It is usually related to pain. You will want to do a temporary muzzle on him to help you keep him from biting in case you cause him some pain while you examine him. Here is a site that shows you how to do this.
Then you will want to check over his tail well. He could also have a problem with his anal glands which will cause a dog to hold their tail down as well and often bite at the rear. The anal glands are 2 sacs on either side of the anus at about the 4' o'clock and 8 o'clock positions. Dogs will normally lick their anus and it could also indicate that they are full. This problem can usually be resolved by emptying out the glands if this is the problem. To empty them or express them, you will want to cover the area with a tissue and press your finger on the dog's anal glands with an upward motion. A foul smelling liquid should come out. If nothing comes out and your dog appears to be in pain, you should take him to the Vet. Your vet can do this easily, as he is experienced at it.
Excellent site on anal glands
There is a condition "cold tail" that Labradors, English Pointers, English Setters, Foxhounds and Beagles sometimes get which causes them to hold their tail close to the body and can cause discomfort. Usually a dog has been swimming, been caught in the rain or bathed. You can read about it here.
It is possible that this is what you are seeing with your dog. With cold tail it sometimes takes up to 2 weeks for the tail to recover. Some owners feel the administration of anti-inflammatory medication aid in a faster recovery.
Dog's have sebaceous glands and perianal glands at the base of their tails. Sometimes, these glands can become clogged and swollen. A warm compress on the spot and cleaning with Benzyl peroxide gel may help with the problem. I would also use some Neosporin or triple antibiotic cream on the area as well. Dogs with this swelling of the sebaceous gland may have a problem with hypothyroidism or a hormonal imbalance, so I would suggest you have your dog seen by your vet if you do not see improvement.
Now another possible issue is that he has ingested a foreign object that has moved through his system and is now at the rectal area of the bowel. It may not be coming through the last little way easily which would also cause them to chase and bite at the tail. Whining would be pretty common for this situation.
Since he is whining, I would not expect it to be pure behavioral. Some dogs do start chasing their tails and it is considered to be a compulsvie disorder, but in your dog's case, it does seem to be more physical. If you fed him a new food recently or given a new treat, it may have triggered an allergic reaction causing some inflammation in the rectal area and severe itching as well. Allergies are quite common in pit bulls. You might try some benadryl at a dosage of 1-2mg per pound every 8 hours. It will take about 30-45 minutes to see some results from the benadryl. If you see improvement, then I would look to see what changed in the dog's environment such as treats, food, cleaning supplies, etc. Read more on allergies here:
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