Urinary tract issues may result from a number of different aetiologies including infection, neoplasia, urolithiasis, neurological disorders, anatomic abnormalities and inflammatory conditions. The name feline lower urinary tract disease (FLUTD) may not be wholly representative of the condition. The role that stress has on the urinary system is starting to become more fully understood. Of the feline patients seen in first-opinion practice, approximately 7% present with urinary disorders (Buffington et al, 2004). With increases in the prevalence of risk factors such as obesity, there is potential for the presentation of more cases.
Urine is a composite of a complex solution of both organic and inorganic ions. Crystals can grow and form when an imbalance occurs in this complex solution. There are several factors that can cause these imbalances. Diet, decreased water consumption, urine pH alterations or relative lack of inhibitors of crystallisation can cause the solubility of a particular crystal to be exceeded. The result is crystal aggregation and growth. Clinical signs of feline idiopathic cystitis (FIC) include haematuria, proteinuria, dysuria, pollakiuria and/or urethral obstruction (Gunn-Moore, 2000). A full diagnostic work-up is recommended in all cases, including blood work and imaging.
It is recommended that all cases are given advice on all aspects of husbandry. Dietary manipulation can aid in reducing the risk factors for uroliths, but there are many other factors that need to be taken into consideration and addressed.
Nutrition
Struvite crystals (MgNH4PO4.6H20) are commonly seen in cats suffering from FIC. Dietary recommendations for these cats include avoiding excessive dietary protein and excessive levels of the minerals that are used within the crystals (i.e. magnesium and phosphorous), and increasing water consumption. Urinary pH needs to be within the recommended range, as the crystals form in an alkaline environment. A range of 5.9–6.1 is ideal for dissolution, whereas 6.2–6.4 is recommended for prevention (Ackerman, 2012). The average urinary pH of a domestic cat consuming a natural diet (small rodents) is 6.3 (Ackerman, 2012). Acidifiers are used to prevent struvite uroliths. Cats receiving long-term dietary acidifiers can suffer from a transient negative potassium balance, with phosphoric acid and ammonium chloride acidifiers. Long-term potassium depletion will stimulate ammonia synthesis at the same site as chronic metabolic acidosis. Acidifying therapeutic veterinary diets need to have potassium levels in excess of the National Research Council's (NRC) minimum allowance of 0.6% (DMB) (Gunn-Moore, 2000). The use of urinary acidifiers alongside an acidifying food is not recommended, as it can lead to metabolic acidosis. The alterations in pH may increase the solubility of some of the solutes within the urine and, in some cases, decrease the solubility of other solutes. This complex and competing interplay between nutritional requirements of the management of oxalate and struvite urolithiasis requires a careful selection in the long-term dietary control of FIC.
Excessive levels of protein need to be avoided in cases where struvite crystals and alkaline urine is present. High-protein level can influence pH; a prime example of this is the difference in urine pH between cats and dogs. Cats have higher protein consumption than dogs, and therefore an increased urinary pH. Increasing the protein level in the diet also increases urinary calcium excretion, uric acid and oxalate excretion. Excess dietary protein should be avoided by feeding cats a food that contains 30–45% dry matter (DM) protein (Gunn-Moore, 2000).
Diets that promote urinary tract health in cats do tend to have a higher fat content. This is owing to the increased energy density which overall reduces mineral intake. When metabolised, fat produces the highest metabolic water contribution, which also benefits the animal. As a result of the increased fat content, some veterinary therapeutic diets are not available in a dry form. Obesity is a major risk factor for FIC, and a diet with higher fat content may not be indicated in this circumstance.
Cats that suffer from FIC and are overweight need to be placed on an obesity diet. Many of which have higher fibre content. The quantity of calcium being absorbed from the digestive system can be reduced by certain sources of dietary fibre. This can be beneficial with cats suffering from recurrent calcium oxalate urolithiasis.
Struvite precipitates form when the urine becomes supersaturated with magnesium, anionic phosphate and ammonium. Therapeutic diets avoid excess dietary magnesium, but low urinary magnesium concentrations have the potential to increase the risk of the formation of calcium-containing uroliths. This highlights the importance of regular urinalysis when on a therapeutic urinary diet. Intake of magnesium and calcium also influences urinary phosphate concentrations.
The addition of sodium into the diet is occasionally used in order to aid in increased water intake. Increasing the salt content of the diet can aid in diuresis and lowers the urine-specific gravity (Kirk, 2000).
Water
Water intake is a vital factor in cats with FIC or a predisposition to FIC. The solute load of the diet influences total water intake by a large factor. Use of a moist diet is preferred, and additional water can also be mixed in if required. Encouragement to increase the consumption of water can also be achieved by increasing access, such as by placing more bowls of water around the cat's environment. A choice over type and size of water bowls needs to be considered. Cats can be deterred by the use of fresh tap water because of the chlorine content. Use of bottled or pre-boiled water, or water that has been left to stand will have little or no chlorine that can be detected by the cat or dog.
Increases in water consumption will increase the total volume of urine produced. Crystals precipitate out into the urine when supersaturation occurs. Urine becomes saturated when the salt content completely dissolves within the fluid. Any additional salt or decrease in the relative fluid volume will result in precipitation of the salts, hence the requirement for large volumes of more dilute urine. Owners are recommended that the animal's urine should remain dilute and have no strong smell; owners may have difficulty determining this as most cats will urinate outside.
Urinalysis should be performed on a regular basis, at least every 3–6 months. Sediment analysis along with pH and specific gravity are all good indicators of overall health. FIC can result in haematuria and proteinuria. Fresh urine samples should be used when performing urinalysis. Samples for bacterial culture and sensitivity should be obtained via cystocentesis. Voided samples and those not examined immediately can have false positives for bacteria and crystalluria. Many owners will need guidance on how to obtain urine samples from their pets.
Feeding a cat with FIC
The choice of diet is dependent on two factors; the body condition of the animal and results of the urinalysis. Correct identification of the type of crystals present (if any) and the pH of the urine is necessary. Use of a diet that promotes urinary health tends to be aimed at preventing struvite formation. Use of these diets in cats with a predisposition to calcium oxalate uroliths may increase the risk of urolith formation.
A full dietary history of the cat is required, including any treats, supplement (especially if containing calcium) and whether or not the owner gives the cat milk. Both treats and processed human food (processed meats) are high in mineral levels, such as phosphorous, and should be avoided. Use of a moist diet is preferable, as is free-choice (ad libitum) feeding. This might not be possible if the cat is overweight with this feeding scenario.
When any animal consumes food, gastric acid is secreted and creates a temporary net acid loss from the body, and alkalisation of the urine. This is referred to as the postprandial alkaline tide. The alkaline tide is caused by secretion of bicarbonate into the blood by parietal cells of the stomach. A transient bicarbonisation is produced and increase urinary pH. Acidifiers in the diet will offset this increase in pH. If the diet is offered ad libitum, the cat will eat little and often. These habits result in a smaller but more prolonged alkaline tide. This can reduce the likelihood of struvite precipitate formation.
The nutrition and urinalysis workshop was sponsored by Royal Canin.