June 2022

In this VETgirl online veterinary continuing education blog sponsored by Purina Pro Plan Veterinary Supplements, Dr. Andy Sparkes, BVetMed, PhD, DECVIM-CA, MANZCVS, MRCVS will review the importance of good hydration in our feline patients. Please note the opinions in this blog are the expressed opinion of the author and not directly endorsed by VETgirl.

Putting Cats on the Path to Good Hydration

By Andrew Sparkes, BVetMed, PhD, DECVIM-CA, MANZCVS, MRCVS
Simply Feline Veterinary Consultancy and Co-Editor, Journal of Feline Medicine and Surgery

If you’re very persuasive, you might lead a cat to water. But can you make him or her drink? While there is a great deal we don’t yet know about hydration in feline patients, we can learn a lot from cat owners if we take the time to talk to them about their cats’ drinking behaviors and preferences. We can also implement early, effective strategies to mitigate damage from chronic dehydration and/or low water turnover.

Are looks deceiving?
As veterinarians, we tend to suspect dehydration when a cat on our exam table exhibits what we consider the “classic” signs of dehydration: sunken eyes, dry mucus membranes and skin tenting. Such signs should never be ignored, but reliance on “looks” alone can lead a practitioner to suspect dehydration when it isn’t there—or, perhaps more importantly, miss it when it is. A middle-aged dehydrated cat may look perfectly normal, whereas a perfectly hydrated geriatric cat can appear low on fluids simply because a lack of subcutaneous fat has caused his or her skin to sag.

That’s why it is important to talk to owners—especially those with senior pets—about their cat’s eating, drinking and elimination habits. Is the cat drinking less? Urinating less? If the cat is on a wet diet, has he or she been eating less than normal—and thus taking in less liquid?

Such information, coupled with a urinalysis and bloodwork, can paint a more accurate picture of a cat’s hydration status. If owners are willing, they might also consider use of technology-driven monitoring devices, such as microchipping their cat to monitor intake from a water bowl or using a smart litter tray that tells them when—and how much—their cat urinates or defecates.

Why moisture matters
If undetected, dehydration can result in significant harm, particularly in older patients that are prone to developing diseases associated with increased fluid loss, such as chronic kidney disease (CKD), hyperthyroidism and diabetes. Cats older than 8 to 10 years are also likely to experience loss of lean body mass, which can further reduce the body’s water reserves.

Maintaining hydration is extremely important to the health of a cat. Recurrent episodes of dehydration, or chronic underhydration or low water turnover, is known to increase vasopressin secretion in both humans and animals, which can lead to kidney damage.1 Underhydration in elderly human patients also seems to be an important factor in impaired cognitive abilities. We need more evidence to prove that the same type of damage or change occurs in cats, but we do know that we will do no harm by catching dehydrated cats early—and we might be able to help slow the progression of certain diseases. Meanwhile, if the cat suffers from a condition such as urolithiasis or feline idiopathic cystitis, increasing fluid intake in order to achieve urine dilution is also beneficial.

This cat is dehydrated. Now what?
The bad news is that if a cat is dehydrated, he or she probably can’t rehydrate through voluntary water intake as quickly as some other species because of the way cats drink water. Like dogs, cats curl their tongues backwards when they lap water, but while dogs form a sort of scoop, cats only touch the surface of the water and “bite” from the water column that is formed, taking in very small amounts of water per lap. Cats also have a fixed frequency of lapping, regardless of their hydration status or thirst drive.

If feeding a wet diet is not an option for a particular cat, it may be possible to implement strategies that encourage them to drink more, even though feline drinking behaviors are admittedly complex and under-researched. Many of us offer behavior-related suggestions to owners, such as keeping food and water bowls apart (the theory is that when wildcats were on the African savannah, they naturally avoided drinking from water sources next to their killed prey) or advice about the size and composition of drinking bowls as well as the option of providing moving water. While some owners swear by these recommendations, the truth is that there are few controlled studies that have investigated these approaches, and those that have been published have failed to find strategies that make a consistent difference.

However, cats are individuals, and each cat has unique preferences. What works well for one client and cat will not necessarily work for another client and cat. Nevertheless, owners can better understand their own cats’ preferences if they are willing to take the time to observe them. The bottom line: Know thy cat!

Consider a hydration supplement
One evidence-supported development in feline hydration over the past several years is the use of nutrient-supplemented water. If a cat needs to optimize his or her fluid intake but is unwilling to eat a wet diet. or if additional fluid intake on top of a wet diet is desired, supplementing with a product like Purina® Pro Plan® Veterinary Supplements Hydra Care™ Feline Hydration Supplement can be an effective strategy. In studies, cats supplemented with Hydra Care increased their liquid consumption by 50% per day when compared with cats fed only water in addition to dry feeding.2,3 Hydra Care is also palatable, which encourages consumption, and contains osmolytes that help drive water into cells.

Preventing dehydration: Start them young
The good news is that a healthy cat typically can maintain hydration, provided he or she is given access to a balanced diet and fresh water. Cats eating a wet diet with a water content of 70% to 80% can derive most of the fluid they need from diet alone, while those eating dry food comprised of approximately 10% water will compensate by drinking more.

One of the best ways to help a cat maintain hydration throughout life is to feed a variety of foods while the cat is still a kitten. By nature, cats are neophilic and as kittens they are usually willing to eat a variety of textures and flavors. Rather than sticking to a single flavor or formulation of food, feeding young cats an assortment of flavors of both wet and dry food early in life can greatly increase the chances that they will be willing to eat wet food later in life if needed to address a particular health condition.

Today we have a growing appreciation for the importance of good hydration in our feline patients. By communicating with owners about their cats’ eating and drinking habits and taking proactive steps when we note hydration “red flags,” we can help delay—and possibly even prevent—damage and disease, while helping to maintain cats’ comfort and quality of life.

1. Bouby N, Fernandes S. Mild dehydration, vasopressin and the kidney: animal and human studies. Eur J Clin Nutr 57, S39–S46 (2003).
2. Zanghi BM, Gerheart L, Gardner CL. Effects of a nutrient-enriched water on water intake and indices of hydration in healthy domestic cats fed a dry kibble diet. Am J Vet Res. (2018) 79:733-744.
3. Zanghi BM, Wils-Plotz E, DeGeer S, Gardner CL. Effects of a nutrient-enriched water with and without poultry flavoring on water intake, urine specific gravity, and urine output in healthy domestic cats fed a dry kibble diet. Am J Vet Res. (2018)79:1150-1159.

PPVS Purina Supplements logo VETgirl blog

Only VETgirl members can leave comments. Sign In or Join VETgirl now!