Fever is an important fiding: now the important work is to determine why fever is present. Infection is one cause, neoplasia (cancer) is another, among other causes, My first suggestion is a chest radiograph (x-ray) to determine if pneumonia is evident. At the same time I would urge blood work--a complete blood count, biochem. profile and thyroid screen along with an auto-immune profile, urinalysis is also indicated. An oral exam of the deep throat is helpful and may need to be done under sedation.
Further diagnostics may be required, potentionally CT scan or MRI. My rule-outs include: laryngeal paralysis, hypothyroidism, myasthenia gravis, esophageal dystonia, dilated esophagous, pneumonia, oral tumor. And the list can go on...
Bottom line is to start the detective work and discard the items on the problem list as the physical exam/history/diagnostics start to accumulate a body of information. Don't be content to throw any more antibiotics at this problem: please have your veterinarian dig deeper. If he is unable, then consult with a referral practice or a veterinary school.
Laryngeal paralysis is more common than thought in Great Danes.
Dr. Van Lienden
Dr. Raymond Van Lienden DVM
The Animal Clinic of Clifton
12702 Chapel Road, Clifton
Virginia, U.S.A. 20124