Thanks for your answers, However the dog passed away.
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Cocker Spaniel Arthritis by: Anonymous
You could consider adding supplements to your cocker spaniels diet.
Glucosamine Chondriotin will help with the arthritis pain and may help to restore joint health.
It will probably take 6 weeks before you notice any improvement.
You may also like to add fish oils or evening primrose oil to his diet. These are essential Omega-3 fatty acids and which help with general health, protect the skin, improve nails and coat appearance and prevent dryness.
I would recommend you ask your vet for his advice before you begin to mess around with his diet.