Ron Hines DVM PhD 4/30/06

Next to tumors and mycoplasmal respiratory disease, more pet rats die of kidney failure than any thing else. Every species has its weakest link. In us, it is often our hearts. Rats do not suffer from the types of heart diseases we do; instead, their kidneys slowly loose their ability to filter blood and cleanse the body of waste. Your rat’s kidneys are composed of millions of tiny filters called glomeruli. As blood passes through these filters, the waste products of protein metabolism are collected and excreted into the urine. These filters also regulate the amount of water and minerals (electrolytes) present in the body. kidney rat kidney rat

As a precaution, Nature provides much more kidney filtering capacity than our bodies require. But the wear and tear of time as well as specific diseases, infections and nutritional imbalances slowly clog and destroy these filters (glomeruli). It is not until seventy-five percent of the filters have been damaged that the level of waste products in the rat’s bloodstream begins to creep up. When I suspect kidney damage in your rat, I assay the amount of two byproducts of protein metabolism in their blood. These byproducts are urea and creatinine – products that give the urine its yellowish color. Normal blood levels of urea (Blood Urea Nitrogen or B.U.N.) and creatinine in rats are 12-20mg/decileter and 0.3-0.4mg/decileter respectively. As kidney function wanes, these numbers begin to increase. The disease that results is referred to as chronic kidney disease, chronic renal failure, renal insufficiency, chronic uremia or chronic interstitial nephritis. One specific subtype is known as polycystic kidney disease.

Many rats with blood urea nitrogen levels of 30 to 40mg/dl seem perfectly content and normal. But by the time two-thirds of the filters are lost and as creatinine levels approach double their normal values certain signs begin. First, the rat will begin to drink more water and urinate more. In this way, its body still cleanses the blood with fewer functioning filters. Each remaining glomerulus filters increasing amounts of water from the blood and in so doing makes up for declining filter numbers. Consequently, the rat drinks more. For reasons not fully understood, these rats also begin to loose weight. As the disease progresses, the pet becomes anemic. Blood phosphorus and potassium increase and blood calcium decreases. They may develop diarrhea. The rat’s appetite decreases and its body becomes more acidic. Blood pressure increases. When I palpate the abdomen of these pets, I feel small hard and irregular (scarred) kidneys. Some times, periods of sickness develop after stresses such as boarding, the addition of other rats to the cage, etc. During these periods of stress the pet drinks less than the amount that is necessary to keep the blood free of toxic waste. Low blood calcium and elevated blood phosphorus cause a second disease to occur, hyperparathyroidism, which results in softening of the bones.

Treatment:
It is important that rats with kidney disease have water available to them at all times. When symptoms occur, your veterinarian may give the pet even more fluids intravenously or subcutaneously. This fluid is soon urinated carrying away waste as it goes They may also administer a group of medicines called diuretics (furosemide, Lasix) to increase urine flow. With these treatments, your pet can regain its metabolic balance. Human beings in this situation begin kidney dialysis to flush wastes from their bodies. We also attempt to lessen the workload on the remaining kidneys by decreasing the amount of protein-waste that they must process. To do this, we place the pet on a special diet. These diets derive more of their energy from fats and carbohydrates that do not tax the kidneys. These diets are also low in phosphorus and basic or alkaline. Sometimes we place the animals on anabolic steroids (stanazolol, Winsterol) and vitamins (B-complex) to encourage red blood cell production and appetite. They may receive the hormone, erythropoietin which also encourages red cell production. Aluminum hydroxide antacids help control digestive disturbances and remove excess phosphorus from the body. Low salt diets help control blood pressure. So although this is a progressive disease with no known cure, a lot can be done to improve your pet’s quality of life.

Diet:
Normal rat chow has about 20% protein. If we lower protein levels to 10% by mixing the rat chow 50-50 with whole aflotoxin-free corn and flax seed, protein levels will be approximately 10 –12 %, which is much less taxing on the rodent’s kidneys. Non-breeding rats seem to subsist well on diets as low as 8% protein. This diet also decreases kidney fibrosis and inflammation due to the anti-inflammatory qualities of linoleic acid contained in the flax.
Diets supplemented with omega-6 and omega-3 polyunsaturated fatty acids and conjugated linoleic acid are also beneficial in managing rats with kidney disease stores (J. Am.Soc. Nephrol. 1998 Jul: 9(7): 1242-8). These products, available from health food stores, decrease the progression of kidney inflammation and fibrosis. The younger the rat when it is placed on a lower protein, supplemented diet, the more beneficial the change and the longer its lifespan should be.

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