If this happens after he has had a fatty treat of some sort it might be pancreatitis. You can read about that here
www.peteducation.com/article.cfm?cls=2&cat=1580&articleid=335
If you feel it might be an arthritis issue then you might want to use glucosamine chondroitin to see if that helps. Glycoflex and Cosequin are two good brands to use.
You might want to do an x-ray of the neck and spine as disc problems or arthritis there can cause pain down through the body too.
Hope this helps you!
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