Daily Water and Fluid Requirements and Needs for Hyperthyroid Cats

Hyperthyroid cat drinking water
in his condo at the Hypurrcat spa

Drinking a healthy amount of water is vital to a cat’s health. Although water is certainly important for clinically normal cats, it is absolutely essential in maintaining and restoring health in sick cats, and that certainly includes cats with hyperthyroidism.

Everything your cat does uses energy, and water plays a critical role in the body's metabolic processes, which regulate all the body's functions (1,2). This is especially true in hyperthyroid cats, in which the metabolic rate is increased, body temperature tends to be elevated, and increased moisture loss through the respiratory and gastrointestinal routes are common.

Many hyperthyroid cats are mildly to moderately dehydrated. Keeping a hyperthyroid cat well hydrated helps ensure that adequate oxygen and vital nutrients will reach all the tissues of the body — this allows the cat to metabolize its nutrients and sustain or restore normal body function. Maintaining adequate hydration also helps absorb the excess body heat typically generated by hyperthyroid cats because of their “revved up” metabolic state (3-5).

The Potential for Dehydration is High in Older, Geriatric Cats

As cats age, they develop a number of important changes in water metabolism that can predispose them to dehydration. First of all, even healthy geriatric cats have higher water losses than younger cats, possibly due to reduced urine concentrating ability even without obvious evidence of overt kidney disease (6,7). In addition, the poor thirst reflect, already present in the younger cat (1,7,8), worsens as the cat ages; again, this reduced sensitivity to thirst commonly leads to a state of chronic dehydration in the geriatric cat.

The potential for dehydration will be exacerbated in cats with concurrent diseases that cause increased thirst (polydipsia) and urination (polyuria), such as diabetes mellitus, chronic kidney disease, or hyperthyroidism. Senior cats may benefit from increased water content via feeding canned foods, ensuring access to fresh water, or flavoring the water (see Water and Hydration Recommendations for Hyperthyroid Cats, below). Older cats do not cope well with changes in daily routine, so any changes to food and water should be made gradually.

Hyperthyroid Cats Commonly Have Increased Thirst and Urination

Thyroid hormones have a diuretic action, an effect that was reported in cats almost 70 years ago (9). In accord with those experimental findings, increased thirst (polydipsia) and urination (polyuria) are frequent clini­cal signs observed in hyper­thyroidism, occurring in over half of affected cats (3-5). Because of that effect, hyperthyroidism (along with kidney disease and diabetes) is one of the three major rule-outs for a cat presenting with increased thirst and urination. Although concurrent primary kidney disease con­tributes to polyuria and polydipsia in up to a third of cats with hyperthyroidism (5), these signs also occur in many cats with­out any evidence for kidney disease.

The precise cause of these signs in hyperthyroid cats without any kidney disease is not always clear. However, the hyperthy­roid state may impair urine con­centrating ability by increas­ing total blood flow to the kidneys, thereby decreasing the solute concentrations in the inner part of the kidney (i.e., the renal medulla). This renal “medullary washout” may cause polyuria with secondary poly­dipsia (5, 10). In other words, these cats drink more to compensate for the increased amounts of water lost through their kidneys.

Alternately, in cats with normal renal con­centrating ability, a central nervous system disturbance caused by hyperthyroidism may produce a “compulsive” primary polydip­sia (3-5,10,11). In other words, these cats develop a compulsive need to drink more water, and the increased urination occurs as a secondary response to the large volumes of water consumed. In these hyperthyroid cats, increased thirst and urination will normalize within a few weeks after successful of treatment of hyperthy­roidism.

In addition, it has been suggested that diseases that promote polyuria and a dilute urine (such as hyperthyroidism, diabetes, or renal disease) predispose to urinary tract infections (12,13). In one study, over 20 percent of cats with untreated hyperthyroidism has a positive urine culture, diagnostic for a urinary tract infection (13). If this infection would spread to the kidneys, pyelonephritis and subsequent renal failure could result (10).

As we discussed in my last post on Daily Water Requirements and Needs for Cats, cats have failed to evolve a strong "thirst reflex" like that of dogs and humans. This inherited weakness of the cat's thirst drive to respond to changes in his or her state of hydration must be considered in the hyperthyroid cat. We must work to ensure that an adequate hydration status is maintained on a daily basis in these cats.

Water and Hydration Recommendations for Hyperthyroid Cats

An important aging change in cats is reduced sensitivity to thirst, resulting in an increased risk of dehydration even in cats with seemingly normal renal function. As animals go, cats require less water than many others, and we often have a difficult time getting cats to drink as much as we would like. Cats with certain health problems, especially those with hyperthyroidism, need to drink more water than an average cat.

But how can we get a hyperthyroid cat to drink more water?
Here are a few hints:

• Place more bowls of fresh water located in different areas of the house —Providing cats with more than one bowl of water in different locations around the house or apartment will encourage the cat to stop and take a sip from each one. I normally recommend at least to three bowls in various locations throughout a cat’s living space.
• Provide larger water bowls —Another way to encourage cats to drink more water is to provide larger water bowls, such as ones designed for dogs, to prevent the cat`s whiskers from touching the sides when drinking. Filling the water level all the way to the top also helps prevent the whiskers from touching the sides of the bowl. A cat’s whiskers are very sensitive; whiskers touching the sides of the bowl can be very irritating for the cats.
• Keep water bowls clean — By nature, cat will not drink stagnant or dirty water. Standing water tends to get warm and stale and can harbor bacteria, dust, and insects. To prevent this problem, it’s important to wash the bowl daily and provide fresh, clean water. In addition, use of stainless steel or ceramic bowls is best, as plastic bowls may lock in bacteria and odors.
• Provide running water — Running water is naturally enticing to some cats. Some cats that refuse to drink out of a water bowl will drink water from a slowly running faucet or a “fountain bowl,” which can provide your cat with running water 24 hours a day. Make sure that the cats are drinking out of the fountain before removing other water bowls.
• Flavor the water or add ice cubes — Adding a little water from a can of water-packed tuna to the bowl of water provides extra flavor to the water, which may entice some cats to drink. Flavoring water with chicken broth is another useful means to convince cats to drink more. Adding ice cubes or chips to the water as a treat will also help in some cats.
• Feed canned food — Canned food has a lot of moisture, so it will provide your cat with much more water than feeding dry food. See my last post on Daily Water Requirements and Needs for Cats for more information about how to calculate the amount of water that the food contains.
• Add water to the food— In some cats, 3 to 4 teaspoons of warm water can be added to the canned or dry food to provide more water. However, some cats do not like food with added water and may refuse to eat it, so this approach must be individualized.
• Filtered or spring water — Some cats prefer filtered or spring water over tap water. However, distilled water is never a good choice, as it may actually flush needed minerals out of the cat’s body. I do not advocate the use of bottled water because of the environmental consequences of the plastic bottles as waste (14), as well as the chemical plasticizers known to leach from the plastic bottles. In addition, it’s important to realize that there is no way to know if the bottled water you buy is really pure and natural, or if it’s just processed and packaged tap water. 

Bottom Line: Water and Hyperthyroid Cats

Since up to a third of hyperthyroid cats have concurrent kidney disease, and up to 20 percent have concurrent urinary tract infections, keeping our hyperthyroid cats well hydrated is of utmost importance. Feeding a canned diet containing 70 to 80 percent moisture together with plenty of fresh water freely available helps guarantee control of water balance in both normal cats and cats with hyperthyroidism.

Again, water serves as the hub of all chemical processes in the body. Ensuring and maintaining proper hydration plays a key role in treatment of all cats with hyperthyroidism.

References 

1. Case LP. Nutrition: feeding cats for health and longevity. In: The Cat: Its Behavior, Nutrition and Health. Iowa State Press, Ames, Iowa 2003;289-327. 
2. Kohn CW, DiBartola SP. Composition and distribution of body fluids in dogs and cats. In: DiBartola SP, ed. Fluid therapy in small animal practice. Philadelphia: WB Saunders Co, 1992;1–34. 
3. Peterson ME, Kintzer PP, Cavanagh PG, et al. Feline hyperthyroidism: pretreatment clinical and laboratory evaluation of 131 cases. Journal of the American Veterinary Medical Association 1981;183:103-110. 
4. Broussard JD, Peterson ME, Fox PR. Changes in clinical and laboratory findings in cats with hyperthyroidism from 1983 to 1993. Journal of the American Veterinary Medical Association 1995;206:302-305. 
5. Mooney CT, Peterson ME: Feline hyperthyroidism, In: Mooney C.T., Peterson M.E. (eds), Manual of Canine and Feline Endocrinology (Fourth Ed), Quedgeley, Gloucester, British Small Animal Veterinary Association, 2012; in press. 
6. Pérez-Camargo G. Feline decline in key physiological reserves: implication for mortality. Proceedings of the Nestlé Purina Companion Animal Nutrition Summit: Focus on Gerontology. St. Louis, MO. 2010, pp. 6-13. 
7. Little S. Managing the senior cat. In: Little, S. (ed), The Cat: Clinical Medicine and Management. Philadelphia, Elsevier Saunders, in press. 
8. National Research Council. Feeding behavior of dogs and cats. In: Nutritional Requirements of Dogs and Cats. National Academies Press, Washington, D.C. 2006; pp 22-27. 
9. Radcliffe CE: Observations on the relationship of the thyroid to the polyuria of experimental diabetes insipidus. Endocrinology 1943;32:415-421. 
10. Nichols R, Peterson ME: Investigation of polyuria and polydipsia, In: Mooney C.T., Peterson M.E. (eds), Manual of Canine and Feline Endocrinology (Fourth Ed), Quedgeley, Gloucester, British Small Animal Veterinary Association, in press.
11. Evered DC, Hayter CJ, Surveyor I. Primary polydipsia in thyrotoxicosis. Metabolism 1972;21:393-404. 
12. Mayer-Roenne B, Goldstein RE, Erb HN: Urinary tract infections in cats with hyperthyroidism, diabetes mellitus and chronic kidney disease. J Feline Med Surg 2007;9:124-132. 
13. Bailiff NT, Westropp JL, Nelosn RW, et al. Evaluation of urine specific gravity and urine sediment as risk factors for urinary tract infections in cats. Veterinary Clinical Pathology 2008;37:317–322.
14. Is Bottled Water Better? Medicine.Net.com  

Daily Water Requirements and Needs for Cats

Running water is naturally enticing
to many cats and is one way to get
cats to drink more water

Drinking a healthy amount of water is vital to a cat’s health. Most people don’t think of water as a nutrient. But considering that water accounts for about two-thirds of a cat’s body weight and serves as the hub of all chemical processes in the body, it's actually the king of all nutrients (1,2).

Water serves many physiological functions: it transports nutrients and oxygen through the blood stream and into the cells, moisturizes the air in the lungs, regulates body temperature, protects and moisturizes the joints and internal organs, and helps eliminate waste products of metabolism through the kidneys and gastrointestinal tract.

Cats Do Not Naturally Drink Much Water

Cats do not normally need to drink very much water. Cats have evolved to obtain their water requirements almost entirely on the moisture content in their food. In the wild, cats obtain most of their water from freshly killed prey (e.g., small rodents, birds, amphibians, and insects), all of which contain about 70 to 75 percent water (3-7). Cats can do well for long periods without drinking any water when receiving canned food containing 67 to 73 percent water (8, 9); however, they will become dehydrated when the water content of the food drops to less than 61 percent (9). Therefore, normal cats eating rodents or birds or house cats eating canned-only foods may obtain enough water in their diets so that extra drinking water may not always be needed (2,10).

It's very important to realize that domestic cats have a diminished "thirst drive" and ideally will derive most of their daily water intake from the moisture contained in their food. In this respect, control of water balance in cats differs markedly from that of dogs and most other animals. When dehydrated, cats are slower to initiate drinking or to drink enough for complete rehydration — one study found that dehydrated dogs will drink enough to replenish 6 percent of their body weight in an hour compared to the 24 hours it takes for dehydrated cats (11).

In response to changes in the water content of food, cats adjust their voluntary water intake less precisely and less rapidly than do dogs. Similarly, their compensatory drinking response to dehydration induced by higher environmental temperatures or concurrent disease is less effective than it is in dogs.

How Much Water Does a Cat Need to Drink?

The amount of water drunk by an individual cat depends on a variety of factors, including the cat's size and activity, the season, and whether the cat's diet includes wet food or dry cat food only (2,10,12). Factors such as high heat, exercise, or lactation can double or triple the amount a cat drinks. And, of course, diseases such as hyperthyroidism, kidney disease, and diabetes will all greatly increase a cat's daily water requirements (I'll talk more about water and hydration in these cats in my next post).

So how much should a cat drink? A normal cat’s daily water requirement ranges from 5 to 10 fluid ounces per day (or an average of 60 ml/kg/day). Cats eating canned food will receive much of their daily water needs from its food, since canned food is about 70 to 80 percent water. In contrast, dry food is only 7 to 10 percent water. Normal cats eating canned food may need to drink less than 1 ounce of additional water per day, whereas a cat consuming only a dry diet may need to drink over 7 ounces per day to stay hydrated. This higher amount of water can be difficult to achieve because cats are not prone by nature to drink large amounts of water.

Will Type of Food (Dry vs. Canned) Affect the Amount of Water a Cat Drinks? 

A cat consuming a predominantly dry food diet will drink more water than a cat consuming a canned food diet. But in the end, when water from all sources is added together (moisture in their diet plus the water they drink), the cat on dry food consumes about half the amount of water required for adequate hydration compared to a cat eating canned food (2, 13).

Put another way, when cats are fed only dry food, they do increase the amount of water drunk but not nearly enough to fully compensate. In one study (12), cats consuming a dry food diet containing 10% moisture with free access to drinking water had an average daily urine volume of 60 milliliters (or 2 fluid ounces). This urine volume almost doubled when the cats were then fed a canned diet containing 75 percent moisture.

Calculating the Volume of Water Provided by the Cat’s Diet

The moisture content of all cat food (both canned and dry) is listed on the product label as part of the Guaranteed Analysis (14). Canned diets usually contain about 75% moisture, so for every 100 grams of food fed, 75 grams (which equals 75 ml) is water. Dry foods, on the other hand, contain only about 10% moisture, so for every 100 grams of food fed, 10 ml if water.

The weight of a standard, larger can of cat food is 5.5 ounces (156 grams). If the moisture content of the food is listed as 78 percent max and the cat eats the entire can of food, he or she would be ingesting approximately 120 ml of water from the food (156 gm X 0.78 = 121.68 ml). Again, if the same cat at 156 grams of a dry food containing 10% moisture, that would provide only 15.6 ml of water.

The weight of a standard, smaller can of cat food is 3 ounces (85 grams). If the moisture content of the food is again listed as 78 percent max and the cat eats the entire can of food, he or she would be ingesting approximately 65 ml of water from the food (85 gm X 0.78 = 66.3 ml). Again, if the same cat ate 85 grams of a dry food containing 10% moisture, that would provide only 8.5 ml of water.

Water Requirements in Cats with Hyperthyroidism

Although water is certainly important for clinically normal cats, it is absolutely essential in maintaining and restoring health in sick cats, and that certainly includes cats with hyperthyroidism. To that end, I'll address the special water needs of hyperthyroid cats in my next post.

References

1. Kohn CW, DiBartola SP. Composition and distribution of body fluids in dogs and cats. In: DiBartola SP, ed. Fluid therapy in small animal practice. Philadelphia: WB Saunders Co, 1992;1–34.
2. Case LP. Nutrition: feeding cats for health and longevity. In: The Cat: Its Behavior, Nutrition and Health. Iowa State Press, Ames, IA 2003;289-327.
3. Myrcha A, Pinowski J. Weights, body composition and caloric value of post-juvenile molting European tree sparrows. Condor 1970;72:175–178.
4. Mutze GJ, Green B, Newgrain K. Water flux and energy use in wild house mice and the impact of seasonal aridity on breeding and population levels. Oecologia 1991;88:529–538. 12.
5. Angilletta MJ. Estimating body composition of lizards from total body electrical conductivity and total body water. Copeia 1999;3:587–595.
6. Austad S, Kristan D. Does caloric restriction of laboratory mice mimic natural food intake of wild mice? Gerontology 2002;42:8–18.
7. Hall JM, Hung F, Zurich MW. The influence of diet on the body condition of the house cricket and consequences for their use in zoo animal nutrition. Zoologische Garten 2003;73:238–244. 
8. Caldwell FT. Studies in water metabolism of the cat. The influence of dehydration on blood concentration, thermoregulation, respiratory exchange, and metabolic-water production. Physiological Zoology 1931; 4:324-355.
9. Prentiss PG. Wolf AV. Eddy HE. Hypopenia in cat and dog: ability of the cat to meet its water requirements solely from a diet of fish or meat. American Journal of Physiology 1959; 196:625-632. 
10. National Research Council. Feeding behavior of dogs and cats. In: Nutritional Requirements of Dogs and Cats. National Academies Press, Washington, D.C. 2006; pp 22-27
11. Adolph EF. Tolerance to heat and dehydration in several species of mammals. American Journal of Physiology 1947;151:564–575. 
12. Seefeldt SL, Chapman TE. Body water content and turnover in cats fed dry and canned rations. Am J Vet Res 1979;40:183–185. 
13. Kirk CA, Debraekeleer J, Armstrong PJ. Normal cats. In: Hand MS, Thatcher CD, Remillard RL, et al, eds. Small animal clinical nutrition. 4th ed. Philadelphia: WB Saunders Co, 2000;291–351.
14. Food and Drug Administration website. Pet food labels—general.