Diabetes Mellitus

What is Diabetes Mellitus? 

Diabetes mellitus is a classical disease in humans and most of us have heard some of the terms used to describe it. In humans, diabetes is broken down into two forms: Type I and Type II. These are also referred to as juvenile onset and adult onset diabetes or insulin dependent and non-insulin dependent diabetes. In short, Type I is the type where the pancreas produces no insulin at all, and Type II is the type where the pancreas produces some but not enough. Many pet owners wonder if dogs and cats have similar categories for their disease.

Understanding Sugar Metabolism

In order to understand the problems involved in diabetes mellitus, it is necessary to understand something of the normal body's sugar metabolism. The cells of the body require fuel in the form of fat or sugar to conduct their daily activities. Some tissues can use either sugar or fat depending on circumstances and some tissues (such as the brain and nervous system) depend almost exclusively on sugar as fuel.

Diabetes mellitus mostly involves the metabolism of sugar (in particular, a sugar known as glucose) so we will focus on the sugar part of the situation. Glucose comes from the diet in the form of starches and sugars that we eat.

Tissues cannot absorb glucose without a hormone known as insulin. Insulin is produced by the pancreas as part of the body's natural blood sugar regulation. Insulin can be considered to be a key that unlocks the door, allowing sugar in the bloodstream to enter the body’s cells. Once inside the tissues, glucose can be burned for fuel or stored, but without insulin, the sugar stays in the bloodstream and cannot be used by the body.

Diabetes in Cats and Dogs

In a diabetic animal there isn't enough insulin. In fact, there may be no insulin at all. Remember that insulin was the key to unlocking the cell so that glucose could be brought inside. With no insulin, glucose cannot get in. Not only is glucose not being taken in and stored, but it is left floating around in the bloodstream in extremely high amounts. The body's tissues are starving and the bloodstream has plenty of glucose to feed them but without insulin, the glucose is unavailable.

Virtually all dogs have insulin dependent diabetes and must be treated with insulin. There is no way around it. Their condition is similar to the Type I diabetic human in many ways.

Most cats have non-insulin dependent diabetes, which has some similarities to Type II human diabetes. The term "noninsulin dependent" might suggest that these cats can get away without insulin injections, but that is not the case. Instead, what this means is that for these cats, the diabetes can resolve if the pancreas improves its insulin-secreting ability. In order to have a chance at changing a diabetic cat back into a normal cat, insulin injections are definitely needed. Alternatively, about 25 percent of diabetic cats are in a mildly diabetic state where it is possible for them to be managed with oral medication. Not all diabetic cats are similar to humans with Type II diabetes. Some diabetic cats, perhaps as many as 25 percent, have more severe hormone issues, such as acromegaly or Cushing's disease, that make them not only insulin dependent but difficult to regulate.

Symptoms of Diabetes

Excessive Thirst & Excessive Urination

Because there is no way to remove the glucose from the bloodstream, blood sugar levels are astronomically high. Normally, the kidney is able to conserve the bloodstream's glucose but its mechanisms are overwhelmed and glucose spills into the urine in high amounts. Glucose is an "osmotically active" substance, which means it is able to draw water with it. All this glucose is therefore pulling lots of water with it, which translates into excessive thirst and excessive urination.

Excessive Appetite & Weight Loss

The tissues of the body are unable to access any of the glucose they need for fuel and are basically starving. Fat is mobilized and muscle is broken down to help feed the tissues but it does not do much good without insulin to bring fuel inside the cells. The patient shows excessive appetite because its body is in a state of starvation. Because the body is rapidly breaking itself down, weight loss is also a classic sign. All the sugar in the urine provides a desirable growth medium for bacteria and urinary tract infection is a common finding in diabetes mellitus.

Cataracts (Dogs Only)

In diabetic dogs (but not cats), a specific type of cataract rapidly develops in the eye when high amounts of glucose enter the lens. Glucose normally feeds into the lens but the amount of glucose coming into a lens in the diabetic state, is at a much higher level. Excess glucose is converted to another sugar called sorbitol, which in turn attracts water. The excess water disrupts the clarity of the lens creating a diabetic cataract, which leads to blindness in almost all diabetic dogs.

Treatment for Diabetes

Insulin vs No Insulin

The first question we always get asked is if cats and dogs with diabetes need to have insulin injections.

Dogs - As the diabetes is permanent, dogs do require insulin injections for treatment

Cats - Diabetes might not be permanent so to start, cats will require insulin injections however there is a chance they might go into remission and therefore may not be insulin dependent long term. 

More about Insulin Injections

Since deficiency of insulin is the problem, it’s not surprising that giving insulin is the solution. You will need to learn to give injections, which is daunting to some owners at first, but almost everyone becomes an expert quickly. First, an insulin type and dose need to be selected. There are several types of insulin medications available and it is not possible to know exactly how much insulin your individual pet will require at first; trial and error is needed. Your veterinarian will make a guess based on what works for other cats and dogs and what has been reported in the literature.

Most pets require injections twice a day, approximately 12 hours apart, following a meal. Because overdose of insulin is potentially an emergency, it may be prudent to start with once a day insulin, just in case.

Insulin has traditionally been given by syringe in a shot. This involves buying a box of syringes and a bottle of insulin, drawing up a measured amount of insulin, and giving a shot. 

Some insulin medications are available from the pharmacy (with a veterinary script) and some are available only through veterinary clinics. Your veterinarian will either provide you with supplies or will give you the necessary prescriptions. Insulin syringes are marked in insulin units (either U-100 syringes for 100 unit/cc insulin or U-40 syringes for 40 unit/cc insulin). Whenever you receive more supplies, always double check these numbers.

It is important to never alter the insulin dose recommended by your doctor. 

Regular Glucose Curve Testing

To determine whether dose adjustments are needed (or if a different type of insulin is more appropriate), your pet will need glucose curve testing where blood sugar levels are monitored every 2 to 4 hours for several hours. This kind of testing tells the doctor how long the insulin injection is lasting as well as what the lowest and highest glucose levels of the day are. It is important to find out when your pet's curve is due. Often in the beginning, it takes several dose selections and several curve tests before the right dose is determined.

A bottle of insulin, when stored properly, should last 6-8 weeks, after that time it should be replaced.

Fructosamine Testing

If your pet is too sensitive for a valid glucose curve at the vet’s office, the fructosamine blood test may be useful. Again, this test looks at average glucose levels so wide fluctuations will not be discovered but at least there is a monitoring option for this situation.

Regulating Difficult Pets

Unfortunately in some cases, some pets are difficult to regulate. Your pet will probably require re-regulation at some point. There may be an underlying reason to sort out. If your pet seems to fit in this category, some reasons could be:

  • Improper administration of insulin. If possible, have your doctor observe you giving the insulin to your pet. Another possibility is that your insulin may be out of date.
  • Rapid insulin metabolism. Insulin wears off quickly in some animals. Your pet may require a different type of insulin or a second injection during the day or even additional injections during the day.
  • Insulin overdose may actually lead to elevated glucose levels (and clinical signs of diabetes mellitus). In this situation, too much insulin brings the blood glucose too low and other hormones respond to bring it back up (and generally over-do it).
  • Steroid administration (such as prednisone, prednisolone, etc.) will interfere with insulin.
  • Progesterone, a female hormone, also interferes with insulin. This may be observed more in some animals such as un-desexed females. 

The Importance of Diet and Feeding

Regulation can generally be worked out on whatever diet the pet is eating but there are some diets and feeding strategies that are helpful. Particularly for those animals that are not attracted to therapeutic diets. 


For dogs, high-fibre diets are preferred as they slow absorption of sugars and help maintain a more regulated blood sugar level. Fibre also seems to make the body's tissues more sensitive to insulin, which also helps with regulation. There are many great Diabetic Prescription Diets available. Diabetic dogs are best fed in two meals, approximately 12 hours apart. After they have eaten their food, their insulin dose can be given.


For cats the strategy is different. Cat seem to do best when fed multiple small meals throughout the day, so they should be allowed access to food at all times. High protein/low carbohydrate diets seem to be the most conducive to regulation for cats with diabetes. These diets promote weight loss in obese diabetics and are available in both canned and dry formulations. There are specific prescription diets, both canned and dry, for diabetic cats.

It is important to talk to your veterinarian about your pet's diet to select an appropriate choice for your pet. You may be advised to avoid soft-moist diets as sugars are used as preservatives. And it is also recommended to avoid feeding your pet breads and sweet treats. If it is not possible to change the pet's diet, then regulation will just have to be worked out around whatever the pet will eat.

Hypoglycemia and Other Things to Watch For


The most serious problem to watch for in diabetic animals is hypoglycemia (low blood sugar). This results from a mismatch in food consumption and insulin dose. If the dose is too high your pet can get hypoglycemia. If the pet doesn't eat, it can get hypoglycemia. Your pet may look simply tired, weak, or sleepy. If she is roused, she will seem drunken or may not be able to fully come to alertness. This can be an emergency and can progress to seizures so it is good to know what to do at home to prevent disaster.

First try to get your pet to eat. If the pet will not eat, give light Karo syrup, honey, or even sugar-water at a dose of one tablespoon per 2.2kg of body weight. The sugar will absorb directly from the mouth so swallowing is not necessary. If no improvement occurs, immediately see a veterinarian as your pet may require emergency treatment.

When your pet is more stable, a glucose curve will be needed to determine why this happened and what a more appropriate insulin dose might be. It is best to make sure that your pet has recently eaten before giving the scheduled insulin dose.

It is important to bring your pet in for a re-check exam and testing if you note any of the following:

  • Your pet seems to feel ill
  • Your pet is losing weight
  • Your pet has a ravenous appetite or lose in its appetite
  • Your pet seems to be drinking or urinating excessively
  • Your pet becomes disoriented or groggy

Dental Issues

It is important for diabetic pets to have their teeth cleaned annually. Dental tartar seeds the body with bacteria and when blood sugar levels run high, infections in important organs can take root. The kidneys and heart are particularly vulnerable. We recommend getting your pet's teeth checked regularly by your veterinarian to monitor its oral health status.

The Important 'Take-Homes' for Pet Diabetes

  • Diabetes mellitus is caused by a deficiency of insulin. 
  • If your pet is diagnosed with diabetes, you will probably need to give it insulin injections as a replacement (But don't stress, it is easier than you think!). 
  • The main symptoms of diabetes is excessive urination, excessive thirst, excessive appetite and weight loss. All of which can be controlled by treatment. Watching for these symptoms is the best way to know how your pet is doing. 
  • The starting insulin dose is going to be based on averages and will be tweaked based on trial and error (depending on test results and control of the symptoms). 
  • Using too little insulin is a problem in the long term but too much insulin is potentially an emergency in the short term. 
  • Be sure you know how to recognise hypoglycemia and what to do about it!