Diabetes mellitus is the most common form of diabetes and occurs in both dogs and cats. It is caused by a lack of the hormone insulin and causes very high levels of blood sugar. It is easily diagnosed by testing the levels of sugar in the blood and is treated by regular injections and a regulated diet and exercise plan (for the dogs!). Well controlled diabetics can go on to lead full and active lives.

What is Diabetes Mellitus?

  • Diabetes mellitus (DM) is the most common form of diabetes in dogs and cats.
  • It is caused by a lack of the hormone Insulin. Insulin is produced by the pancreas, one of the abdominal organs.
  • Insulin allows the sugar in the blood to move from the blood stream to the rest of the body, without insulin the sugar cannot move, and the levels in the blood become very high.

What causes Diabetes Mellitus?

  • Diabetes Mellitus (DM) is caused by a relative or absolute lack of insulin. ( A relative lack of insulin is where the insulin levels may be only low, or even normal, but it is not as active as it should be)
  • Type 1 or Insulin Dependent Diabetes Mellitus (IDDM)
    • This is a primary lack of insulin, the pancreas simply stops producing the hormone
    • It is more common in dogs than cats.
    • It can occur in younger animals, where the pancreas is faulty, or has been destroyed by autoimmune attack.
    • It can also occur in older animals who have had repeated bouts of prancreatitis (inflammation of the pancreas which eventually leads to its destruction)
    • It is irreversible.
  • Type 2 or Non-Insulin Dependent Diabetes Mellitus (NIDDM)
    • This is more common in cats but can occasionally occur in dogs.
    • It is more common in older, overweight animals.
    • In these animals the body becomes resistant to insulin, so the levels in the body become higher and higher but the blood sugar levels do not fall.
    • If caught early enough, and the underlying factors, particularly obesity, are corrected, it can be reversed.
    • Despite its name, insulin is usually required to control it.

Risk factors for developing Diabetes Mellitus

  • Obesity – This is a huge risk factor for developing DM, especially in cats. In overweight animals their bodies are more resistant to insulin, which means they have to produce more than normal to keep the blood sugar levels stable. This puts increased pressure on the pancreas, which eventually leads to it becoming ‘exhausted’ and no longer able to produce insulin.
  • Age – older animals are more likely to become diabetic, especially if they are over-weight. In dogs it tends to occur in animals older than 7 years, cats tend to be over 10 years old.
  • Sex – In dogs, entire females are most at risk from becoming diabetic. This is because the hormone ‘Progesterone’, which is produced when bitches are in season, counteracts the effects of insulin, causing the blood sugar to rise. All diabetic entire bitches should be spayed once their diabetes is stabilised. In cats, diabetes is more common in males.
  • Breed – certain breeds of dog have been shown to have a higher risk of becoming diabetic, they include; terriers (for example Jack Russels, Cairns, Tibetan), Schnauzers, Poodles, English Setters, Rottweilers and Collies.


obese cat, ginger and white, fat, very fat

Obesity is a huge risk factor for the development of diabetes, particularly in cats


Clinical signs of Diabetes Mellitus

  • Drinking more and urinating more (polydypsyia and polyuria); this is the major symptom of diabetes in both dogs and cats and the one most owners notice first. However, it is not exclusive to Diabetes, and can be caused by many other problems.
  • An animal should drink about 50ml of water per kilo of body weight per day. If you are concerned about your pets water intake, measure it over a few days and take the figure to your vet, along with a urine sample.
  • Weight loss – This does not occur in all cases, but as the body cannot use the sugar in the food for fuel, as it is trapped in the blood by a lack of insulin, it has to burn its own resources, which are its fat reserves. Weight loss can occur despite a normal or increased appetite.
  • Increased appetite ( polyphagia); again, this doesn’t occur in all cases. As the body is unable to extract the sugar from the diet, it is effectively starving, therefore some diabetic animals become frantically hungry as the body is desperate to gain nutrition from the food.
  • Cataracts – cataracts occur when the lens of the eye becomes cloudy, and causes the eye to become blind. They can develop quickly and are sadly common in dogs, despite treatment.
  • Urinary tract infections (Cystitis); these are generally only uncovered when the vet takes a urine sample, as they are often symptom free. Diabetic animals have very high levels of sugar in their urine, which makes it a very easy place for bacteria to grow and set up an infection.
  • Plantigrade stance – This is a symtom occasionally seen in cats and is caused by ‘Diabetic Peripheral Neuropathy’. The nerves to the hocks of the back legs become weak and the cat starts to walk with its back legs sunken to the ground. It is normally reversible once the Diabetes has been treated.

This cat is showing a classic plantigrade stance. It has ‘sunk down’ on its back legs and is unable to straighten them. It can still walk.


Diagnosing Diabetes Mellitus

  • Blood tests – these are the mainstay of diagnosis in Diabetes, your vet will be looking for raised levels of sugar (glucose) in your pets blood stream. There may be other changes as well, for example liver changes – this is due to the liver being under stress because it is primarily responsible for breaking down the bodies tissue when the sugar cannot be used. Most liver changes are reversible once the diabetes is treated.
  • Normal animals will have blood sugar levels between 5-9mmol/l. Diabetic animals can have levels greater than 20mmol/l
  • Urine tests – the presence of sugar in the urine is what confirms the diagnosis of DM. Also, it is common for animals to have urinary tract infections, which will show up on the urine tests. Sugar does not generally appear in the urine until the blood levels are greater than 15mmol/l.
  • Clinical signs – the clincial signs listed above are very typical of DM, and these, together with blood and urine tests, will confirm DM is present.

Treating Diabetes Mellitus

  • Treatment of diabetes in most cases involves injecting the animal with insulin on a daily basis.
  • However, this is not the case in all cats and dogs, some animals can be controlled with weight loss and dietary changes.
  • Generally treatment with insulin is lifelong, especially in dogs.
  • Sometimes, in cats, the Diabetes can be reversed, especially if the cat was overweight when diagnosed..
  • Diabetic dogs will also need their diet and exercise levels carefully controlled.
  • Some animals can be treated with ‘Oral Hypoglycaemics’, tablets to bring the blood sugar levels down. However, these often do not work very well and, if used, rarely cut out the need for insulin altogether.
  • Entire female dogs should be spayed once their DM is stable, the fluctuations in hormones during a season will cause their DM to become uncontrolled.


  • There are several different types of insulin, which are shown in the table below. your vet will chose the one most suited to your pet and your lifestyle.
Type of insulinTrade nameOnset of actionDuration of actionInjections per day Example Pictures
SolubleInsuvet0-30 minsShort (up to 4 hours)Used only to stabilise diabetics, not for long term use
1 hour6-20 hoursTwice daily
UltralenteHypurin2-8 hours14-24 hoursOnce daily
PZIInsuvet1-4 hoursup to 24 hoursOnce daily
  • Most vets will chose to start your pet on twice daily insulin, this tends to give a better overall control than injecting just once a day.

There are several different types of insulin available, your vet will chose the one most suitable for you and your pet.


Storing insulin

  • Insulin should always be stored in the fridge, even if the bottle has not been opened.
  • Once a bottle has been opened, you must discard it after 1 month, even if it is not finished.
  • Caninsulin is available in 2.5ml bottles, which can be very useful for animals which require small doses.
  • Do not allow the insulin to freeze, this will destroy it.
  • Always store the bottles upright.


Injecting insulin

  • This is often the most daunting thing about treating animals with diabetes, but it is not as difficult as it may first appear. Your vet will take you through the procedure step-by-step.
  • Do not worry about hurting your pet, the insulin needle is very small, they will hardly feel it!
  • There are now insulin pens available which can make drawing up doses and injecting pets much easier.  They aren’t available for all types of insulin, so you will need to discuss with your vet if they are suitable for your pet.

Injecting insulin, a step by step guide;

  1. After getting the insulin out of the fridge, swirl the bottle gently to mix the contents. DO NOT SHAKE the bottle, this can damage the insulin molecules.
  2. Tip the bottle upside down, and push the insulin needle through the rubber top of the bottle. There is usually a circle embossed on the rubber, aim for the middle of that.
  3. Pull down the syringe plunger, go further than the amount you need. Flick the syringe if any bubbles appear, these should then rise to the top and can be pushed back into the bottle.
  4. Push the plunger upwards until you have the correct insulin dose in the syringe.
  5. Remove the needle from the bottle and replace the needle cap.
  6. Ensure your pet is comfortable and not stressed.
  7. Pick up the scruff on the back of the neck. This will ‘tent’ the skin. Aim the needle towards the bottom of the ‘tent’ and push it through the skin.
  8. Once you are sure the needle is through the skin, press the plunger.
  9. Remove the needle from the skin, and place it immediately in a secure container. Your vet will be able to supply you with a medical ‘sharps’ bin.

To watch me demonstrating how to inject a cat with insulin, watch this video;

Injecting tips

  • Ask your vet to clip the hair away from the back of your pets neck. This allows you to better see where you are injecting, and therefore you can be sure the needle goes through the skin.
  • It is important your pet eats before they have their insulin. A good tip is to inject them while they are eating, they are much less likely to notice!
  • The graduations on the insulin syringes are very small, and can be difficult to see. There are different volumes of syringes, so in some the graduations are further apart. Also, some syringes come with magnifying lenses, to help make the markings on them clearer. Ask your vet about this.
  • If you are concerned, or have any questions, speak to your vet, they will always be happy to help.



This is a very important aspect of a diabetics treatment, When animals eat, their blood sugar levels will rise, so controlling what and when they eat is very vital to gain good control of their blood sugar.


  • Dogs are similar to people in that after they eat, their blood sugar immediately climbs, therefore their eating patterns and insulin injections need to be carefully matched and controlled.
  • It is very important that dogs eat before they are given their insulin. If they are injected, and then don’t eat, there is a danger their blood sugar levels could fall dangerously low. If you are at all concerned about injecting your dog, always speak to your veterinary surgeon.
  • Dogs who are given insulin once daily should be fed 1/3rd of their daily ration after their injection in the morning, and then 2/3rds about 8 hours later, when the insulin will have its peak effect, and the blood sugar levels are likely to be at their lowest.
  • Dogs who are injected twice daily should be fed 1/2 their daily ration with each injection.
  • Diabetic dogs should receive no treats or snacks between meals. Treats will cause the blood sugar levels to rise and the insulin may not be able to control them. Also, diabetics are often overweight, and if they can lose weight, their condition will be easier to control and their general health will improve.
  • The ideal food for a diabetic is low in fat and high in fibre. There are prescription diets available for diabetic dogs, and these can be very helpful. To learn more about diabetic diets, click here


  • In cats, the after eating rise in blood sugar is less marked, so it is not as important as in dogs to ensure they eat at certain times.
  • However, it is important that they do eat at some point, otherwise the insulin could cause the blood sugar to fall to dangerously low levels.
  • Cats who are fed wet food should be fed in a similar fashion to dogs, twice daily is best.
  • Cats who are fed dry food can also be fed twice daily, but the biscuits can be left down to allow your cat to graze, which is how most cats will eat.
  • It is important that the total food intake is monitored closely, diabetics should eat the same amount every day in order to ensure good control.
  • Diabetic cats are often overweight, so controlling their food intake is very important. If they can lose weight, their diabetes will be more easily controlled, and even reversed in some cases.
  • There are diabetic prescription diets for cats. It can be a very good idea to feed these. In some cats, the diabetes can be controlled by diet alone. For more information on diabetic diets, click here.


  • It is important that a diabetic animals exercise levels are consistent from day to day, exercising burns calories and can lower blood sugar levels.
  • In cats it is not normally necessary to do anything at all, they are very good at regulating their own energy levels, generally doing very little!
  • In dogs, it is obviously more important. Dogs should be given the same level of exercise every day.


  • There are tablets, ‘Hypoglycaemics’ which can be given to try to reduce the blood sugar levels in some cases.
  • They stimulate the production or release of insulin.
  • They are not commonly used and are often not very successful as most diabetic animals can no longer produce insulin, or are resistant to its effects.
  • However, your vet may suggest them if the animal has difficult to control diabetes, or they cannot be injected with insulin.

Monitoring diabetes

It is very important to regularly monitor the blood sugar levels of a diabetic animal, especially in the first few week after the diagnosis, when your vet will be calculating the correct dose of insulin that needs to be given.

Blood glucose

  • Measuring the blood glucose of a diabetic is very easy, vets will use a measuring device called a ‘Glucometer’. This needs only a very small blood sample, and will give an accurate blood sugar reading.
  • The best way to monitor a diabetic is to take a ‘glucose curve’. Over the course of a day, the vet will take blood samples every hour or so and plot the rise and fall of the blood glucose levels.
  • A blood glucose curve allows the vet to see what is happening over a day, and decide whether the insulin doses need to be altered.
  • Most blood glucose curves are taken just in the daytime, but some will be taken over 24hours, especially in difficult cases.
  • Insulin needles are normally used to take the blood samples, these are very small so your pet will hardly feel it.
  • In some cases, the vet may ask you to run a blood glucose curve at home, animals in the vets can become stressed and this can alter the results.
  • It is important to remember that blood glucose levels will be increased in stressed animals, particularly in cats.
  • There are now glucose monitors that can be attached to your pets skin which measure sugar levels over a couple of weeks.  They need a special reader to get the results but they can be a very effective, and stress free, way to find out well controlled they are.


Urine testing

  • When the blood sugar levels climb too high, generally over 15mmol/l, the kidneys start to send the sugar into the urine, where it can be detected.
  • Therefore, sugar present in the urine can indicate an animals blood sugar levels are too high.
  • In some cases, your vet may suggest you test the urine on a daily basis in the morning, in order to monitor your pets blood sugar levels, and change the insulin levels accordingly.


  • This is a specialised blood test that is sometimes used to monitor diabetics.
  • It requires a single blood sample and will give an indication of the average blood glucose levels in your pets system over the preceding few weeks.
  • It can be used to monitor diabetics who are unsuitable candidates for glucose curves, for example aggressive or very stressed cats.

Diabetic complications

Difficulty in stabilising the diabetes

  • It is common in the first few weeks to months of a diabetic being diagnosed that there will be many changes to the insulin doses and regime.
  • However, some patients may have difficult to control diabetes and need more intensive treatment.
  • All aspects of the animals life need to be considered, such as diet, exercise, and weight.
  • Vets may use several glucose curves over several weeks in order to find out the problem and find the right insulin dose.
  • Entire bitches must be spayed, the hormonal changes during a season will disturb the insulin control.
  • There are some diseases which can underlie the diabetes and make it difficult to control, such as Cushings disease or Acromegaly. These can also be diagnosed by blood tests.
  • If your pet is proving difficult to control, do not despair, the huge majority are eventually very well controlled, but some take longer than others.

Hypoglycaemia (Low Blood Sugar Levels)

  • This is potentially a very serious problem, and comes about when the blood sugar levels of a diabetic fall too low.
  • It can occur for many reasons for example;
    • the animal is accidentally given too high an insulin dose,
    • the animal is injected with insulin but then doesn’t eat
    • The animal, usually dogs, over exercise and burn up too much energy.
  • A hypoglycaemic episode is most commonly seen 6-8 hours after insulin has been given, as this is when it has its peak action in the body.
  • The signs of hypoglycaemia are;
    • Your pet becomes shaky or weak
    • They seem unable to walk, staggering or stumbling
    • If left untreated they can collapse and fall into a coma
  • If you are at all concerned you should contact your veterinary surgeon immediately for advice, or take your pet to the vet.
  • It is important to try to raise their blood sugar levels as quickly as possible, your vet can do this by putting them on a drip containing glucose but at home you can;
    • If they are conscious, feed them a sugary treat such as a biscuit or honey
    • In cats you can just feed them, or try to put sugar or honey into their mouths or rubbed onto their gums.
    • Glucose tablets or powder are easily available from your local chemist or your vet, and are good to have on hand for a diabetic animal.


  • This will generally only occur in an untreated or very poorly controlled diabetic animal, but it is a life threatening condition and must be treated immediately.
  • It occurs when the blood sugar levels have been too high for too long and the body can no longer cope.
  • Clinical signs of ketoacidosis include
    • Sudden onset lethargy and depression
    • Weakness, your pet may be unable to stand, or stagger when they walk
    • Drinking and urinating very large amounts.
    • Vomiting
    • Collapse
    • Sweet smelling breath – this is typical of ketoacidosis, but not all people can detect the smell.
  • An animal showing signs of ketoacidosis should be taken to a vet immediately. The vet will take blood and urine samples to confirm the diagnosis and start intensive treatment to try to save them.
  • Ketoacidosis is a life threatening condition and the animal will die if they are left untreated.

Being the owner of a diabetic animal is demanding, but also hugely rewarding when you see your pet respond to the treatment and become their old selves again. There is no doubt it is a huge commitment on your part, but your vet should always be available to help and answer any queries.

Please note, this is an advice only website, if you have any specific concerns or queries about your pet, you should contact your veterinary surgeon.

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