References
Moisture matters: a focus on feline hydration
Abstract
Water intake in cats is important both in health and disease. While healthy cats with free access to water are adept at maintaining a good water balance, cats can be susceptible to dehydration if the homeostatic mechanisms controlling hydration are disrupted. There are a number of situations in which promoting water intake can be beneficial, particularly in cats with increased water losses (for example, chronic kidney disease; diabetes mellitus; cases of vomiting or diarrhoea), decreased intake of water (for example, as a result of inappetance), and in cats with conditions such as feline lower urinary tract disease. However, cats are often considered ‘poor drinkers’, so increasing their water intake when it is needed can be challenging. This article discusses the water requirements of cats and why they may be susceptible to dehydration. It also explores strategies to successfully encourage water intake in cats and evaluates some of the evidence behind the recommendations.
Water requirements in cats can vary significantly between individuals depending on water losses, which are affected by a number of intrinsic and extrinsic factors including physical activity and ambient temperature.
Daily water needs for healthy cats are only marginally defined and are typically calculated by one of two methods: a bodyweight basis (millilitres of water per kilograms of bodyweight) or water:calorie ratio (millilitres per kilocalorie metabolisable energy ingested) (National Research Council (NRC), 2006; Zanghi, 2020). The NRC recommends calculating the energy needs of the pet on a kilocalorie per day basis and providing 1 ml water per 1 kcal (NRC, 2006) — although lower daily water to calorie ratios of 0.6–0.8 have been reported in healthy cats (Zanghi et al, 2018a; 2018b).
Given the variations between individuals, such equations only ever provide an approximation, which will require monitoring and adjustment depending on the individual. In healthy animals, water requirements are rarely estimated as they are adept at managing water balance and hydration, but such calculations can be useful in hospitalised patients to ensure fluid needs are met, and in studies to help assess the efficacy of different strategies used to encourage fluid intake.
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