Introduction
Diabetes mellitus is a chronic, or long-term, disorder that occurs in both dogs and cats. Diabetes affects approximately one in 150 dogs. The number of cases has increased dramatically over the past 30 years, but the mortality (death) rates have dropped at the same time. This is due to a better understanding of the disease, early diagnosis, and improved treatment.
The disease is characterized by insufficient production of the hormone insulin or a decreased response to insulin in the body (insulin resistance). Insulin is released by the pancreas in response to higher than normal glucose levels in the blood. Insulin sends signals that result in glucose being taken up by cells, being used for energy, and stored as fat to restore normal blood glucose levels in a healthy animal. Diabetic dogs are incapable or inefficient at controlling blood glucose levels.
Just as in humans, there are two types of diabetes found in pets. Type 1 is characterized by destruction of the insulin producing beta cells so that the animal produces limited amounts of insulin. Often the animals are insulin dependent or require injections of insulin to control blood glucose levels. Type 1 (sometimes referred to as juvenile diabetes in humans) is the most common in dogs. Type 2 (referred to as adult onset diabetes in humans) is distinguished by a decreased response to the body’s insulin levels or improperly functioning beta cells from the pancreas. Type 2 diabetes may or may not require insulin injections, depending on its severity. Type 2 diabetes may develop as the animal ages.
Causes
Diabetes occurs in a large number of dogs, but there tends to be a higher risk as they age, with onset often between 7 and 9 years of age. Unspayed female dogs tend to have slightly higher risk than other groups. Genetics may play a role in development, with some breeds of dogs having higher risks. While research on what breeds of dogs are at highest risk varies, Samoyeds and Keeshonds are among those that are at higher risk. Although age and reproductive status are major risk factors for diabetes, the highest predisposing factor appears to be obesity and limited physical activity. Most dogs with diabetes have nonfunctioning insulin-producing cells in their pancreas, related either to immune destruction or secondary to severe pancreatitis.
Symptoms
The general symptoms of diabetes in dogs include excessive urination and thirst, increased appetite, and weight loss. These are often the signs that lead pet owners to the vet for diagnosis of the disease. Diabetes can also result in a decrease in food consumption. The animal may also be depressed or inactive. As the disease progresses, the animal may develop cataracts and/or kidney disease. If diabetes is uncontrolled or not regulated, the dog may develop foul-smelling breath that is due to the buildup of ketones in the body. This is called diabetic ketoacidosis and is a medical emergency. Animals with diabetes also are less resistant to infections and may have decreased wound-healing abilities.
Diabetes affects how animals are able to metabolize nutrients in their diets, with carbohydrate metabolism being most severely affected. One obvious sign is the inability to handle blood glucose. Because of the lack of insulin, glucose cannot be removed from the bloodstream and spills over into the urine. Dogs increase urine production to dilute the glucose in the urine, resulting in increased water and electrolyte loss. Such a loss can result in dehydration, low blood pressure, and decreased renal blood flow.
Fat metabolism is also affected. In dogs with diabetes, there is decreased lipid production from glucose and increased mobilization of fatty acids for energy use. This interaction leads to an increase in overall blood lipid levels. Because of the increased fat use, acetyl CoA can build up in the blood and produce ketone bodies that increase the risk of ketogenesis or acidosis. If uncontrolled, both of these conditions can cause a diabetic coma and death.
A lack of insulin also increases protein breakdown and increases glucose production from amino acids. This leads to excess nitrogen excretion, which pulls more water to the urine to dilute it out and increases the risk of dehydration and leads to excessive thirst and urination.
Diagnosis
Diabetes in dogs is diagnosed through measurement of glucose in the urine and blood following a fast. Other blood chemicals may also be examined.
Management and treatment
Most diabetic dogs require insulin injections to control blood glucose levels. Many owners are concerned about their ability to perform this task, but with proper instruction, it is quite easy. The injection amount and needle size are small so that the dog barely notices. Giving your dog lots of positive attention at this time will make it a more enjoyable experience. Your veterinarian will prescribe the proper dosage and injection schedule for your dog. Care must be taken to provide insulin injections in proper timing in relation to meals and glucose intake. Veterinary instructions should be followed carefully.
After the initial diagnosis, it can sometimes take several weeks to develop and carry out a good management plan for your diabetic dog. Monitoring of blood and urine glucose levels is very important during this time, and you should work with your veterinarian to develop a plan that you can implement. Intact females should be spayed to reduce the hormonal effects of the estrous cycle on glucose metabolism. In addition to insulin injections and glucose monitoring, diet and exercise also play an important role in the management of this chronic disease.
Several nutritional factors are important in diabetic management. First, the animal’s calorie intake should be monitored. In some cases, returning to ideal weight can correct the symptoms of diabetes if caught early. In addition, weight loss will improve the energy balance in the animal’s body. Timing of meals is important. Feeding several small meals will decrease the stress on the animal’s body by preventing a large intake of glucose or energy-containing compounds at one time. For dogs that have lost weight in the initial stages of the disease, maintaining a healthy weight will also be important.
The nutrient composition of the diet is critical to the treatment of diabetes in dogs. For many nutrients, the dietary requirements stay the same. The majority of research has focused on altering carbohydrates in the diet of diabetic animals. The use of the glycemic index helps us find foods that decrease the post-meal increases in blood glucose levels. By choosing low glycemic index foods, we can decrease the dependence on insulin to control blood glucose levels. In addition, it prevents blood glucose from spiking as high as with higher glycemic index foods.
The addition of dietary fiber works to decrease the release of glucose into the blood stream. Soluble fiber tends to have a more pronounced benefit in animals with diabetes than insoluble fiber. Furthermore, added fiber increases the ability to feel full faster and can help decrease obesity symptoms. Owners should be aware that there are some considerations to make when including high fiber levels in the diets of diabetic animals. Changing your dog suddenly to a higher fiber diet can result in the animal having increased stool volume and possibly flatulence. Because of these factors, only moderate increases in fiber are recommended.
Your veterinarian may recommend transitioning your dog to a weight loss diet or a prescription diet designed for dogs with diabetes, depending on the severity of the symptoms. These diets are designed to decrease the amount of glucose entering the blood stream and improve the symptoms of the disease. Carefully monitoring food intake is critical in dogs with diabetes. You should consult with your veterinarian before making any changes to the dietary plan recommended. Any changes should be made slowly . It is important that dogs receiving insulin eat on a regular schedule. Use of treats and table scraps is strongly discouraged in diabetic animals unless approved by your veterinarian.
If your dog is overweight, development of a weight loss plan should include added structured exercise for the dog. Training or longer walks will aid in weight loss and can result in use of excess energy from the diet to help decrease signs of the disease. Before starting a new exercise plan, review the plan with your veterinarian to ensure it meets your dog’s needs.
With some special care and planning, diabetes can be well managed in the dog. It is not currently a curable disease, but its effects and symptoms can be controlled with proper medication, monitoring, and nutritional management. Many diabetic dogs go on to live full and healthy lives.
Lisa Karr-Lilienthal, Ph.D. – University of Nebraska-Lincoln