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Kidney disease:

The kidneys' jobs are to get rid of nitrogen waste products left over from using proteins and maintain electrolytes and a variety of other blood chemicals at their correct levels.

When an animal is born it has about 4 times as many kidney units (called nephrons) as it needs. These nephrons get damaged by a variety of processes and eventually, when 75% of them have been destroyed, there is only just enough kidney function left. Beyond this point, the animal is said to suffer from kidney insufficiency. It will seem quite normal, but urine and blood samples will start to show abnormalities. If we could find all the pets with kidney problems at this stage we could do so much more to help them. By the time they show obvious illness they are in kidney failure.

If degenerative processes are not treated, there tends to be a vicious circle effect whereby the body tries to keep up kidney function by increasing the blood pressure and this causes damage to the delicate filter beds which are at the top of each nephron. The regulation of blood pressure inside the filterbeds is very complex and several methods are available to help reduce the harmful effects of increased pressure.

In cats, the use of vasodilator drugs has been found to help, but this has not yet been demonstrated in dogs. Controlling the amount of phosphate in the blood can also play a part. Phosphate levels rise when the kidneys can no longer control calcium loss adequately and the body extracts mineral from the bones to keep up the calcium level. Phosphates are released in this process and have an effect on the blood pressure regulation in the kidneys.

Special diets are a potent part of the management of kidney insufficiency and work in several ways. They are low in phosphates and have reduced protein levels. Reducing food protein is not a simple matter as there are certain protein elements (amino acids) which are vital and cannot be made in the body. Cats are more complex than dogs in this regard as they have much less ability to modify amino acids to suit their needs. So a restricted supply of high quality protein is needed by the animal with impaired kidney function.

Some diets have a specially balanced essential fatty acid combination which helps to regulate inflammatory processes which can be involved in kidney damage.

The other main dietary change which helps pets with kidney insufficiency is a special fermentable fibre source which encourages growth of harmless bacteria in the large intestine. These bacteria need nitrogen to grow and extract nitrogen waste from the contents of the intestine and lock it inside the bacterial cells. More nitrogen wastes then diffuse into the intestinal contents from blood vessels in the intestine wall, thus removing them from the blood and reducing the amount the kidneys must eliminate.

So diets are a main element in the management of patients with failing kidneys but animals in serious kidney failure are reluctant to eat, so if we are to give such patients effective help we must identify them earlier by means of blood and/or urine testing of pets which seem perfectly well. By the time that kidney failure (as opposed to insufficiency) is obvious it is usually too late to control the problem and it is usually fairer to put the animal to sleep.

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