The health of a dog can be a big factor a dog’s behavior. Always talk to your vet first about your dog’s aggression. See medical issues related to aggression for greater detail.
Response to illness, injury or chronic pain, such as underlying medical problems such as painful muscles, joints, and teeth, an uncomfortable gastrointestinal system or neurological problems. The loss of hearing or sight can cause a dog to be caught off guard, resulting in aggression. Aggression can be toward nearest human or animal.
Some diseases causing aggression could be Hyperadrenocorticism (Cushing’s disease), hypothyroidism, diabetes mellitus, brain tumors, cognitive dysfunction. Increased aggression around food and an increased appetite could be related to hormonal diseases.
**Aggression categories compiled from:
Clinical Behavioral Medicine for Small Animals, Karen L. Overall, M.A., V.M.D., Ph.D. Diplomate, American College of Veterinary Behavior, Department of Clinical Studies, School of Veterinary Medicine, University of Pennsylvania, Philadelphia. Pennsylvania, Mosby, Inc. 1997
The Dog Who Loved Too Much: Tales, Treatments, and the Psychology of Dogs, Dr. Nicolas Dodman, BVMS, MRCVS, Bantom Books, 1997