Do you constantly find your dog lapping up water from his bowl? If so, it's important to take a closer look at why he or she might be thirsty. Excessive thirst in dogs can be a sign of many different medical conditions, and it's crucial to get your dog checked out by the veterinarian if you notice this symptom. In this blog post, we will discuss the most common causes of excessive thirst in dogs. We will also provide tips on how to know if your dog is drinking too much water, as water consumption can vary and a slight increase in consumption may not be a problem.
What are the mechanisms that regulate thirst in dogs?
Thirst and water intake is a complex process that is regulated by the hypothalamus, and pituitary gland, both of which are in the brain; and the adrenal glands and kidneys. Mechanisms that stimulate thirst will result in the release of anti-diuretic hormone (ADH) from the pituitary gland. ADH works on the kidneys to promote water reabsorption. Any process that interferes with the normal action of ADH can result in excessive thirst in dogs.
What defines excessive thirst in dogs?
Excessive thirst or polydipsia is defined as excessive water consumption. Water consumption greater than 100 milliliters per kilogram of body weight per day (>100 mL/kg/day) is considered excessive. Individual dogs however can consume water in widely varying amounts, and their water consumption can also fluctuate from day to day. Most veterinarians will have the dog owner measure their dog's water consumption over a 3 day period.
Another factor that may suggest your dog is drinking too much water is the amount of urination. If there is excessive thirst in your dog combined with increased urination, this is another sign that he should be evaluated by a veterinarian as the water consumption is likely too high.
What are the most common causes of excessive thirst in dogs?
Many different medical conditions can cause excessive thirst in dogs. The following are some of the most common:
Diabetes mellitus
Diabetes mellitus is one of the most common causes of increased water intake and thirst in dogs. With diabetes, blood glucose levels are high and this causes the kidneys to excrete water into the urine as opposed to reabsorbing water back into the body. This will stimulate the thirst mechanism to prevent dehydration from occurring. Diabetes mellitus in dogs will cause increased appetite (polyphagia) early in the course of the disease in addition to excessive thirst.
Kidney disease
Chronic and acute kidney disease can result in excessive thirst in dogs. In kidney disease, the kidneys are not able to properly filter toxins and waste products from the blood. As renal damage occurs, tubular destruction will affect the kidney's ability to reabsorb water. Fanconi syndrome in dogs is an example of a renal disease that can cause excessive thirst.
Cushing's disease
Cushing's disease is a disorder caused by an overproduction of cortisol, which is a hormone produced by the adrenal gland. Dogs with Cushing's will often drink excessive amounts of water and urinate frequently as the high levels of cortisol affect how the kidneys handle fluids by interfering with anti-diuretic hormone (ADH) at the level of the kidneys. Cushing's disease in dogs will also cause an increased appetite (polyphagia) in addition to polydipsia (increased water intake).
Hepatic or liver disease
Liver disease can cause excessive water intake and thirst in dogs because of decreased urea production. Urea helps the kidneys to reabsorb water back into the bloodstream due to its hypertonic effects. Through complex processes, medullary washout, hormone metabolism difficulties, and excessive thirst may all occur as a result of hepatic failure. Portosystemic shunts in dogs can also result in increased thirst and water consumption.
Diabetes insipidus
Central diabetes insipidus and nephrogenic diabetes insipidus are not uncommon causes of excessive thirst in dogs. Diabetes inspidus is different than diabetes mellitus ("sugar diabetes"). With central diabetes insipidus, the hypothalamus (a part of the brain) is not able to send messages to the pituitary gland that controls ADH release. This results in excessive thirst and subsequently increased urination amounts. Nephrogenic diabetes insipidus is caused by any disease process that interferes with the kidney's ability to respond normally to ADH, resulting in excessive thirst and urination.
Hypercalcemia
Increased blood calcium or hypercalcemia is another potential cause of excessive thirst in dogs. Hypercalcemia can be caused by a variety of different things including, malignancy (cancer), certain types of infection, and certain medications.
Hypercalcemia causes excessive thirst in dogs by impairing the action of ADH in the kidneys (i.e. secondary nephrogenic diabetes insipidus). As water is lost in the urine, the body will attempt to counteract the loss of water by stimulating water intake and thirst.
Pyometra
Pyometra is a uterine infection that commonly occurs in unspayed female dogs. The exact mechanism is unclear, however, pyometra is thought to disable the effects of ADH, resulting in increased water intake.
Corticosteroid medications
Corticosteroids such as prednisone or dexamethasone are used to treat a variety of different diseases in dogs. One of the side effects of taking corticosteroids is excessive thirst due to their hormone-like effects on the body. More specifically, prednisone will antagonize the effects of ADH and therefore prevent the kidneys from reabsorbing water as it filters.
Excessive thirst in dogs can be caused by a variety of different medical conditions. However, excessive water intake combined with increased urination is one sign that something may be wrong with your dog and should be evaluated by your veterinarian as soon as possible to prevent dehydration from occurring. If you think your dog has any of these conditions and would like more information, please contact your veterinarian. For Kitchener dogs, the veterinarians at our animal hospital are happy to answer any questions you may have about excessive thirst in dogs and will help you to determine the best course of action for your dog.