Diabetes Mellitus in Cats and Dogs
by Dr Greg Martin BVSc MACVSc
What is Diabetes?
Diabetes mellitus is a disease syndrome that results primarily from a
deficiency of insulin. Insulin is hormone that is produced by the
pancreas, a gland located in the abdomen next to the duodenum (small
intestine). Within the pancreas, small groups of cells called "islets"
produce hormones, while the bulk of the gland produces the digestive
enzymes. Insulin is the major hormone that allows body tissues (such as
the liver and muscles) to use the glucose in the blood, and therefore
insulin lowers blood glucose levels. Insulin also has a variety of other
effects on various tissues. In diabetics, either lack of insulin from the
pancreas or reduced action of insulin in body tissues leads to an increase
in blood glucose levels. Accompanying clinical signs can vary, but
increased urination is common. With time, weight loss often occurs;
however diabetics may be overweight at diagnosis as obesity reduces the
response of body tissues to insulin.
Diabetes may also cause medical emergencies. This may be due to
exceptionally low blood glucose, which can lead to "diabetic coma".
Alternatively, the disorder "diabetic ketoacidosis" is associated with high
blood glucose, dehydration, and increased ketones in the blood and may lead
to collapse and fatalities. Despite the potential for serious
complications, diabetic cats and dogs may have only mild clinical signs
when the disease is diagnosed.
Some of the long term complications associated with chronically elevated
blood sugar that occur in diabetic people may also occur in diabetic pets,
such as kidney failure, loss of nerve function in extremities, hypertension,
blindness, and (in dogs) cataracts. Due to their shorter life span, pets
develop fewer long-term complications from diabetes than people, and
diabetic cats and dogs have a good chance of a normal life span if properly
Diabetes mellitus should not be confused with diabetes insipidus, which is
a different hormonal disease.
What causes diabetes?
Diabetes may occur as a primary disease, or may occur secondarily to
another disease. Here is a brief summary of the types of diabetes:
This type of diabetes occurs due to immune system destruction of the
insulin-producing (beta) cells of the pancreas. This is the predominant
form of primary diabetes in dogs, but is rare in cats. There may be some
genetic component to the cause of diabetes in dogs. Because this type of
diabetes results in total absence of insulin production, patients with this
form of diabetes must be treated with insulin injections. In human
medicine this has lead to type 1 diabetes being referred to as "insulin
dependent diabetes mellitus" or IDDM. It is generally recommended that
female dogs with diabetes be spayed as the hormonal release associated ith
estrus or pregnancy tends to destabilise control of the diabetes.
This type of diabetes is not as well defined in its cause, but is
characterised by obesity, loss of tissue sensitivity to insulin, and
deposition of a precipitate called amyloid into the pancreatic islets.
This is the type of diabetes often developed by people later in life. The
pancreas of type 2 diabetics may be producing no, too little, normal
amounts, or even excessive amounts of insulin, but this insulin is failing
to achieve its normal action. Type 2 diabetes is the most common form of
diabetes in cats, but is rare in dogs. Humans with type 2 diabetes can
often be treated without using insulin, therefore type 2 diabetes in people
is often referred to as "non-insulin dependent diabetes" or NIDDM. Most
cats with type 2 diabetes do require insulin for successful treatment,
therefore the term NIDDM is not appropriate as a synonym for type 2
diabetes in this species. A particular feature of diabetes in cats is
that it may be transient in nature, the condition resolving with time. The
pathological basis of this "transient diabetes" is yet to be fully
determined, and there is currently no way of predicting whether diabetes
will be transient or permanent at the time the condition is diagnosed.
This is where diabetes is occurring secondarily, as a result of another
disease, disorder, or drug treatment. This may or may not necessitate
treatment for the diabetes as well as the associated condition. Diseases
that may result in secondary diabetes in cats and dogs include: Cushing's
disease (hyperadrenocorticism), hyperthyroidism, acromegaly, and others.
Commonly used drugs that may cause diabetes in cats and dogs include
progestens and corticosteroids. With extended use of these drugs the
diabetes may be permanent, with diabetes persisting after drug treatment is
ceased. Generalised disease of the pancreas, such as that caused by an
invasive tumour or pancreatitis may result in diabetes if a sufficient
proportion of beta cells are destroyed.
Insulin injections are necessary for the treatment of most dogs and many
cats in which diabetes has been diagnosed. Preparations of insulin
intended for human use are often prescribed, although there is a veterinary
insulin preparation called "Caninsulin" available in some countries. The
pharmacology of insulin is complex, involving differences in the insulin
molecule between the different species, a multitude of different insulin
drug formulations, and differences in the way the various injectables
behave when used in different species. There have been few detailed
studies into the pharmacological effects of insulin in dogs and cats,
although there is much clinical experience with some insulin types.
It is generally regarded that the intensive treatment regimes, as used by
many human diabetics, are not practical for use in cats and dogs. The
intensive regimes involve multiple daily blood glucose measurements at
home, and multiple daily injections of precisely calculated dosages of
insulin. The aim of insulin therapy in pets is to attain reasonable
control of blood glucose levels and the clinical signs of diabetes by using
once or twice daily injections of medium to long acting insulin compounds.
As there is considerable variation between individual responses to a given
insulin, an initial trial period is usually undertaken with the pet staying
at the veterinary hospital for blood glucose monitoring. Some cats and
dogs will be able to be managed with once daily injections, others will
require twice daily treatment. Once stabilised on a dose schedule,
management at home may be done either by a fixed dose plan or by measuring
the glucose in the urine using dipsticks and adjusting the insulin dose
accordingly. As the patient requirements for insulin tend to change over
time, periodic rechecks are essential. Rechecks usually will involve a
clinical examination, plus in-patient testing of blood glucose over one or
The importance of dietary management of diabetes in humans is well known.
Meals are timed to coincide with maximum insulin action, and specific
quantities and types of food are advised. High fibre diets are used to
reduce the peak elevation of blood glucose that follows eating. For pets,
high fibre diets should be especially formulated or chosen from available
commercial preparations to ensure consistency of calorie content, and
nutritional completeness. Timing of meals and the use of high fibre diets
is an important component of diabetes therapy in dogs. The timing of the
meal is dependent on the type of insulin being used and the response of the
individual dog as established by serial blood glucose determination. Meal
feeding of cats may not be possible as many cats prefer to browse, eating
many small snacks throughout the day and night. Cats may also refuse to
eat high fibre diets. However, preliminary studies show that high fibre
diets are beneficial to feline diabetics.
Of greater importance is that the animal attains the optimum weight,
especially in obese animals as this will reduce the insulin demand, and in
cats may eliminate the need to give insulin at all. Reduced calorie high
fibre diets are particularly suitable for this purpose.
In animals that are underweight, it is desirable that weight is gained and
that the animal attains normal weight. Very calorie dense diets should be
avoided, especially those that are high in soluble carbohydrates.
Anorexia is particularly dangerous in the insulin treated diabetic animal,
as the blood glucose may become dangerously low if food is not eaten to
balance the insulin dose. It is more important that the insulin treated
diabetic eat something rather than nothing, even if it is not the most
suitable food. Efforts should be made to adjust the diet gradually over a
period of days or weeks rather than making sudden changes.
Drugs that promote insulin secretion or modify insulin action are used in
human diabetics either alone or in combination with insulin treatment. Few
of these drugs have been evaluated for safety or effectiveness in dogs and
cats. The sulphonylurea drugs that promote insulin secretion have been
evaluated in dogs and cats. They are usually unsuccessful in dogs, but a
proportion of cats with relatively mild diabetes may be able to be managed
on the drug glipizide alone. However, the tablets need to be given twice
daily by mouth, and some owners find that once daily insulin injections are
more convenient as a treatment. Other drugs with similar properties
require further evaluation before recommendations for use can be made.
Drugs that are given in people as adjunctive therapy, such as
anti-hypertensives and cholesterol-lowering drugs are not currently used in
Further information on diabetes in cats and dogs:
Veterinary Clinics of North America "Diabetes Mellitus" Volume 25, number
3. May 1995. Editors: D.S. Greco and M.E. Peterson. W.B. Saunders & Co,
Textbook of Veterinary Internal Medicine - Diseases of the Dog and Cat.
4th Edition (2 volumes), 1995. Editors: S.J. Ettinger and E.C Feldman.
W.B. Saunders & Co, Philadelphia, USA.
The Waltham Book of Clinical Nutrition of the Dog and Cat. 1st Edition,
1994. Editors: J.M. Wills and K.W. Simpson. Pergamon Press, Oxford, UK.
The Cat: Diseases and Clinical Management. 2nd Edition, 1994. Editor:
R.G. Sherding. Churchill Livingston, New York, USA.
Dr Greg Martin BVSc MACVSc
Diabetes Research Group, Department of Companion Animal Medicine and Surgery, Faculty of Veterinary Science, University of Queensland, Australia
Article is Copyright 1996 by its Author and Cindy Tittle Moore. We reprint with permission.
DISCLAIMER: One of my concerns in writing a column like this is that I
am not seeing the animal, and what I get from folks in ASCII isn't
always going to be the whole story. So I cannot provide diagnoses, or
really tell you to ignore or treat a given problem. I hope the
information provided guides you in making good health care decisions
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Last updated 02/06/06