Hello, my name is***** and I have over 20 years of experience as a veterinarian.
I am concerned that Chester is getting very thin even with a good appetite and seems uncomfortable lethargic today.
When we see weight loss with an apparently normal or increased appetite we need to worry about disease processes that either don't allow him to digest and/or absorb the food he is taking (such as diabetes, liver disease, primary intestinal or pancreatic disease including cancers) or those that lead to a higher metabolic rate such as cancer or systemic infections.
If he were drinking more and urinating a tremendous amount, diabetes would be a very likely cause of his symptoms. Sometimes early on with diabetes we only see weight loss. Secondary urinary tract infections are common with diabetes, which would explain his foul smelling urine.
Diabetes is controlled with diet and insulin therapy.
Has he had any testing done to achieve a diagnosis?
Ideally he should have a complete blood count and biochemistry profile with a urinalysis checked to start. These tests often give us the information that we need.
If those aren't diagnostic then it is time to move on to more specialized testing. I recommend checking vitamin B levels to look for signs of intestinal disease, a test for pancreatic insufficiency called a TLI, and an abdominal ultrasound to look for signs of changes in the walls of the intestines as well as evaluating his organs. He may need an endoscopy to collect biopsies of his intestines if they look abnormal.
In the meantime you might try feeding him a higher calorie prescription food called Hills a/d or Iams Maximum Calorie from your veterinarian and make sure he has access to plenty of fresh, clean water.
Please let me know if you have any further questions.