Feline Urologic Syndrome (FUS)
Dysuria, hematuria, cystitis and urinary tract obstruction are all signs which may be seen with feline urologic syndrome. The incidence of the syndrome is quite high. In fact, some statistics say that as high as one out of ten cats seen in veterinary hospitals have problems relating to FUS.
The incidence seems fairly equal in males and females, although most urinary obstructions occur in males. Without proper dietary or medical management, it is estimated that 50% – 70% of all cases will have a recurrence.
Various factors have been suggested as causes of FUS, such as: infection, alkaline urine, age of castration, endocrine imbalance, high ash in the diet, high dietary magnesium, phosphate or nitrogen, low water intake, obesity, dry cat foods, confinement and less frequent urination. The cause is likely to be several factors acting together and may not always be the same set of factors.
Urine pH is an important factor in urinary crystal formation. In the wild, cats normally produce an acid urine with a pH of 6.0 – 7.0, due to their high meat diet. The vegetable ingredients in cat foods frequently result in a neutral or more alkaline urine.
After a meal, urine pH increases and remains elevated for one hour or more as a result of the “alkaline tide” phenomenon. Many researchers believe that the increase in alkalinity which normally occurs after eating plus the increase in minerals in the urine from food being digested may lead to a crystal formation in the urine and FUS.
To minimize the crystal formation, some researchers recommend keeping the urine pH below 6.6. Below a pH of 6.6 struvite crystals remain in solution, whereas above a pH of 7.1 crystallization spontaneously occurs.
Studies are being done to see whether it is better to feed a cat free choice or to feed 1 – 2 large meals per day. Feeding free choice usually means the cat is eating 10 – 20 small meals a day and with each meal the urine pH rises and remains elevated for a short period. If one or two large meals are fed, the urine pH increases to a greater degree with each large meal and remains elevated for a longer period.
The question is whether one situation is more conducive to stone formation than the other. Remember that in regard to urine pH several factors are involved, not only is the feeding interval important but also the type of food fed and the mineral composition of the diet.
The majority of cases of FUS have calculi, microcalculi or crystals present in the urinary tract. Bacteria and viral infections are rarely involved and when a urinary tract infection is present, it is believed to be secondary and not a cause of FUS.
In 81.9% of the cases of FUS the calculi are composed of struvite. Struvite contains magnesium, ammonium and phosphate. The urine of a cat is usually quite high in ammonia and phosphorus due to its high protein diet. The levels of magnesium and phosphorus in the urine relate closely to the intake of these minerals in the diet.
Three factors seem to be important in calculi formation:
- A high concentration of calculi-forming constituents in the urine.
- pH of the urine that is favorable for crystal formation.
- The presence of urine in the urinary tract for a prolonged time. Calculi may cause an urethral obstruction or irritate the urinary tract leading to mucus secretion and formation of a mucoid plug causing urethral obstruction.
The mineral content of the urine is an important factor in urinary crystal formation. The minerals in urine can be influenced by diet, efficiency of digestion, urine volume and kidney functioning. Altering the diet is one way to change the mineral content of the urine.
Most commercial cat foods that are made with soybean meal and bone meal are high in magnesium. Most cat foods on the market are 4 – 18 times the minimum magnesium levels recommended by the NRC due to the type of ingredients used in making the food.
Understand that magnesium levels in the food can closely relate to urinary magnesium concentration, but there are several precautions to be considered. For one, the magnesium in the food may not be highly bioavailable and much less is absorbed and utilized than expected.
The caloric density of the food is very important. Dry cat foods on a dry matter basis may contain the same level of magnesium as canned foods. As the energy concentration of dry foods is less, cats must eat more dry foods to meet their needs and so get higher levels of magnesium.
High levels of ash in the diet are frequently associated with high levels of magnesium. But this is not always true as ash is considered to be all the noncombustible materials in a diet. So it not only includes magnesium, but also sodium chloride and calcium salts.
Still some believe that if a cat is FUS-susceptible, the ash in the diet should be less than 5% on a dry matter basis. This statement can be made as long as the magnesium and phosphorus levels are also low in this low-ash diet.
Urinary mineral levels cannot be considered without also considering urine pH. If urinary pH is near neutral and magnesium levels are high in the diet, the incidence of FUS increases. If, however, the urine pH is acid, the high magnesium levels are usually of no problem.
Also if urinary pH is high, FUS may result with low urinary magnesium levels. So urinary magnesium concentration and urinary pH are related in the development of FUS.
Another factor in crystal formation is the length of time urine remains in the urinary tract. Cats are able to highly concentrate urine and go long intervals without voiding. Being a descendant of the desert cat of North Africa, cats can drink less water and concentrate urine to a greater degree than other mammals.
The amount of water consumed is affected by salt intake, condition of kidneys, age and dry matter consumed. It has been found that cats consume less water in relationship to dry matter on dry foods than on canned foods, so urine volume is also less. Water intake is not only an important consideration in FUS, but also in renal failure, as well as in sulfonamide administration.
Commercial dry cat foods have been considered a possible cause of FUS. They are higher in vegetable ingredients than most other types of foods and so lead to a more neutral and even slightly alkaline urine. Dry cat foods have a similar magnesium level on a dry matter basis as canned foods, but their lower caloric density requires a greater intake to meet energy needs.
Furthermore, as mentioned, cats seem to consume less free water to dry matter on a dry food diet than a canned diet. Some researchers also believe that, as dry foods tend to be higher in fiber, more water is excreted in feces and therefore, less through formation of urine.
These factors have led researchers to conclude that cats on a dry food diet would have an increased incidence of FUS and many studies support this view. One study, done with specific pathogen-free cats on dry food diets, did not find any association between a dry food diet and increased incidence of FUS.
In summary, FUS seems to have a multifactorial etiology. Factors of urinary pH, urine mineral concentration and length of time urine remains in the bladder are known to affect calculi formation. As dietary changes can alter these factors and possibly lead to a decreased incidence and recurrence of FUS, focusing on nutritional management may be a good path to follow until further research is available.
Nutritional management is a very important part of managing renal failure. Proper dietary alterations can slow the progression of renal disease and decrease signs of uremia. The goal of dietary management should be to reduce the end-products of protein metabolism which are eliminated by the kidneys, such things as protein metabolites and phosphorus.
Some suggest that in renal failure less than 25% of the calories in the diet should be from protein. Another source says that protein should be adequate in amount to meet requirements, but reduced so as to maintain a blood urea nitrogen of less than 60 mg / dl.
Reduced protein is recommended in patients showing clinical signs of uremia that are azotemic, hyperphosphatemic and in moderate to severe renal failure. In patients not showing signs of uremia a low protein diet is controversial.
Many sources recommend restricting dietary protein in all animals with reduced renal function, regardless of the severity. Higher protein diets have been shown to increase glomerular filtration rate and renal blood flow which may be harmful and lead to further renal damage.
Restricting protein in the diet not only reduces the wastes of protein metabolism, but may reduce progression of renal failure. A restricted protein diet also decreases dietary phosphorus and so may decrease the risk of hyperparathyroidism and osteodystrophy.
As chronic renal failure develops, the kidney loses the ability to excrete phosphorus, which leads to a high serum phosphorus level. As a result, serum parathormone levels increase, which may cause further damage to the renal tubules.
To prevent the use of the body’s own proteins for energy, make sure the animal is consuming sufficient calories in the diet. Feeding small meals several times a day, instead of a single large meal, may also help reduce catabolism of body protein. Make sure that plenty of drinking water is always available.
If severe proteinurea is present and the animal has hypoalbuminemia, it may be necessary to supplement each four ounces of food with one egg or two tablespoons of cottage cheese. If polyuria exists, there may be excessive loss of B-vitamins in the urine, so diets formulated for use in renal failure patients frequently are supplemented with B-vitamins. Proper dietary management in renal failure may slow progression of the disease and reduce uremic signs.
The aims of dietary management in hepatic disease are to restore liver glycogen and reduce the workload on the liver. Energy provided in the form of starch or simple sugars is tolerated well.
The liver helps in the metabolism of the wastes of protein breakdown, therefore protein in the diet should be at a moderate level, so the demands on the liver will be lessened. If the protein intake is too high in an animal with hepatic failure, encephalopathy may occur.
Proteins in the diet should be of high biologic value, such as eggs and liver. Ensure that the diet provides adequate calories so that the body does not utilize body fat and protein stores for energy. If bile salt excretion is impaired, there is a decreased ability to use fats, so restrict fats in the diet to less than 1.5%.
Avoid the usage of medium chained triglycerides in hepatic failure, as they are mainly metabolized in the liver. Certain fatty acids may also induce encephalopathy, if the diseased liver cannot metabolize them.
Ascites, which occurs in liver failure, may be due to portal hypertension, which results in loss of vascular fluid and activation of the renin-aldosterone system.
In this case, the ascites is not a result of hypoalbuminemia. Therefore, if ascites is present, a low sodium diet may be recommended. These measures will decrease the stress placed on a poorly functioning liver and help relieve some of the clinical signs of liver failure which may be present.
Infection, nutritional deficiencies, metabolic disorders and trauma frequently lead to anorexia in cats. If prolonged, anorexia may lead to hepatic lipidosis and jaundice. The aim is to maintain an intake of protein and energy to meet the needs of the body and to prevent the development of a fatty liver.
The safest and easiest way to feed an animal is via the gastrointestinal tract. Feeding through the gut is less likely to lead to a fatty liver and increased production of secretory IgA improves resistance to infection.
So if the gut is functional, use it as the means of nutrient intake whenever possible. Appetite stimulation, force-feeding and tube feeding are methods that can be used. If the gut is nonfunctional, parenteral means must be used instead.
To stimulate appetite, warming the food enhances aroma and may help in encouraging the cat to eat. If nostrils are plugged, clean them. Being able to smell the food is very important in appetite stimulation. Providing a very palatable diet that is the same as the one provided in the animal’s home environment may help.
Force-feeding may be used if it does not result in a high level of stress. It may work in a debilitated animal if done gently and with patience and reassurance. Cats that are stronger will usually fight this procedure.
Tube feeding may be recommended, as it is faster and less stressful than force-feeding. Blend one-half can of a formulated, high energy diet and 3/4 cup water together, then strain the mixture through a kitchen strainer. Administer enough of the mixture to meet the cat’s energy needs in two to three feedings per day.
Another method which is occasionally used on a very temporary basis is to administer diazepam. Most cats who are physically able to eat will do so when given 0.1 – 0.5 mg diazepam intravenously. Have food available at the time of injection. Then 1 – 2 mg is given orally to maintain appetite.
This should not be used for more than two days. Anorexia is a very challenging problem, but recognize that lack of nutrient intake of even a few days adversely affects the entire body. The body’s ability to fight the disease or heal the trauma is lessened when nutrients are absent.
Obesity is a problem in cats, as it is in many other domestic species. Obese cats are frequently on a diet of gourmet canned foods and may refuse to eat other types of commercial foods. The owner may be supplementing the canned food with high caloric table scraps and may be unaware that a problem even exists.
Initially, a good history must be taken, including a good diet history of types of food eaten, amounts and intervals of feeding. A complete physical exam should be done to rule out health problems.
Determine an optimal body weight for the animal and estimate the time required to safely attain that weight. Set realistic short-term goals, such as the goal for weight loss after one week. It is considered safe for a cat to lose about one-half pound the first week and about three pounds over twelve weeks.
Initially try a diet which is 20% – 30% lower in calories than the previous diet6 • If this results in no weight loss or a minimal loss then change to a diet providing 65-70% of required calories to maintain a cat at its optimal body weight (about 35 calories / pound of optimal body weight / day).
To lose one pound of body fat, caloric intake must be decreased by 3,500 kcal. A diet high in fiber and low in fat is recommended for weight loss, generally less than 10% fat (on dry basis) and greater than 15% fiber. It may be necessary to gradually introduce the new diet.
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