"Barney just isn't himself anymore. He seems not to hear us when we ask him to do the things he's always done. Is he developing bad behavior?" This is a question that veterinarians are often asked about older pets. It is important to recognize a simple fact; Old age is not a disease.
Senior pets often develop health issues that can appear initially as changes in behavior. These changes can be misinterpreted as a sudden loss of normal good behavior in the pet. In fact the behavior changes do not stem from a willing desire to be "bad". They are due to several common medical conditions that can be present in our older pets such as: cognitive dysfunction syndrome, osteoarthritis, and endocrine imbalances.
Cognitive dysfunction syndrome (CDS) is a condition of reduced dopamine production in the brain. This can lead to a reduction in your pets' ability to recognize normal behavioral stimuli. They appear less interested, less active, or less familiar with you and their environment.
Osteoarthritis (OA) affects one in five dogs in the United States. Many times owners think that the sudden loss of their pets' interest in playing or being active is due to old age. In fact OA causes chronic discomfort and loss of ability to use the affected joint(s) properly. This leads to a reduction in desire to move or respond to environmental stimuli.
Endocrine imbalances also can have a profound effect on your pets' behavior. Low or high levels of thyroid hormone or steroids in your pets system can have a substantially negative impact on their response to their environment.
If your pet starts to behave atypically, the first thing you should do is consult your veterinarian. In many cases simple screening tests or blood samples can help discover the true reason for your pets' change in behavior. Medications are available that can help return your pet to his normal behavioral ways.
Source: Peter H. Eeg, B.Sc., DVM