Hello, this is Dr. Linda. I hope I can help with your question today.
I am sorry for your concerns about Fetch. It is always concerning when a pet appears to be in some discomfort.
I must start out by saying that without a hands on exam, I will not be able to give an exact evaluation of what might be troubling Fetch. But in an older, large breed dog, osteoarthritis is always at the top of my list. Osteoarthritis can affect any moving joint ( hips, elbows, knees, etc ), but can also be a problem in the the spine. Arthritis in the neck, or upper or lower back, is quite common in dogs. Often there is no limp, but the dog is just somewhat "off". X-rays will show the classic lesions in the vetebrae of the neck &/or back.
There may also be some soft tissue problems as well. Perhaps Fetch injured a tendon, ligament, or even bruised a muscle in his daily forays outdoors. More serious would be some underlying disease or chronic condition.
The fastest way to an answer is of course a visit with your veterinarian. Otherwise, you can try a short course of aspirin, no more than for 3 days. An 80 pound dog can have 1&1/2 of a regular strength aspirin ( buffered or coated preferred ) every 12 hours. If this helps, then there are much safer options for Fetch available through your veterinarian that you can keep him on for long periods, if necessary. Using a good brand of a glucosamine/chondroitin sulfate product ( like Dasuquin made by Nutrimax ), can help keep his joints as healthy as possible as he ages.
Fetch, at 8 years, is similar to an 51 year old person. We just can not participate in things the same way as when we were younger.
I hope this makes sense, & you find the information useful. Please let me know if you have any additional questions or concerns.