The most common form of diabetes in dogs is diabetes mellitus or sugar diabetes, which occurs due to either a lack of production of insulin (the hormone that regulates glucose levels) by the dog's pancreas, or because of an insensitivity to insulin. When blood glucose levels are too high, it's excreted in the urine, causing an excessive loss of water in the process. The dog then compensates by drinking more. Sometimes dogs with diabetes will lose weight as they burn through stores of fat and muscle trying to make glucose. Other symptoms can include cataracts, increased appetite, exercise intolerance and recurrent infections. What's more, when fat is burned to make glucose, compounds called ketones are also produced, which, if allowed to build up in the bloodstream cause ketoacidosis, which makes the dog very unwell and requires intensive treatment.

It's likely several factors are involved. Dogs will sometimes get diabetes as a direct result of being afflicted with another illness or infection. Certain diseases, especially the ones affecting the pancreas, may trigger an abnormal production of insulin. For example, Pancreatitis (inflammation of the pancreas) may result in the destruction of the cells in the dog's pancreas that are required for blood glucose regulation, which may then lead to diabetes mellitus. Prolonged courses of steroids can also bring about diabetes as they can affect the normal functions of the pancreas, thereby slowing down the production of insulin. Obesity, as in humans, also brings with it a higher risk of diabetes, but sometimes its onset is because of simple genetics. Certain breeds of dogs, such as Golden Retrievers, German Shepherds, Miniature Schnauzers, Keeshonds and Poodles tend to show a higher incidence of diabetes.

Diabetes can be confirmed through blood and urine tests, which will show high concentrations of glucose in the blood and urine, as well as high ketone levels. In cases where the underlying cause cannot be diagnosed, diabetes cannot be cured, it can only be managed. As with diabetes in humans, this is commonly done with daily insulin injections, as well as special dietary and exercise regimens.

It has been suggested that foods with a low glycaemic index are better choices for diabetic dogs (just as is the case with humans) as they improve overall blood glucose control. In general, diabetic dogs should be fed a diet high in complex carbohydrates and fibre to promote slow glucose release into the bloodstream. Dry food usually contains higher amounts of fibre so are usually preferred for diabetic dogs. Commercial 'prescription' diets for diabetic dogs are also available. These diets are usually balanced in respect to fibre and glycaemic content, as well as the other nutritional requirements of a dog. If you choose to feed your dog a homemade diet, be sure to make the food consistent every day to avoid unnecessary fluctuations in blood glucose concentrations. Regular check-ups with your vet will be necessary to check that the insulin dosage, diet and exercise regimen continue to keep the blood glucose level in check.

Depending on the cause, severity and treatment, clinical signs may resolve themselves within days, or take up to several months after the commencement of treatment. If left untreated, Cushing’s Disease is progressive and has a poor prognosis. If controlled well on medication, the dog’s prospects are good. However for dogs with advanced tumours, especially if they are causing neurological symptoms and there are metastases (spread of the tumour to other parts of the body) the prognosis is usually bleak.