Tortoises live for a very long time and so their kidneys can degenerate through ages, just as can happen in humans. Kidney problems can also occur in younger animals though if they are given a diet too high in protein, which puts a strain on the kidneys. The uric acid which is a waste product of the protein metabolism can accumulate in the kidneys and joints, causing pain to the tortoise and possible problems with stones in the kidneys, which can cause irreparable damage.
What the kidneys do
The kidneys are very important organs in any animal, filtering and concentrating the urine so that the water which is drunk stays in the body helping keep blood volume up and making sure that all organs that need hydration – the brain, the liver, the bowel, for example – have enough fluid to function. If the kidneys were not there, all fluid would just pas straight through and many waste products of metabolic processes would not be excreted properly, causing problems with brain function and muscle tone, as well as many others. In short, kidney health is vital.
A tortoise may develop uric acid stones or calcium stones if there is an imbalance in its diet – too much protein or calcium – or if the kidneys are not working well. Dehydration gives the kidneys an immediate problem, as there is not enough fluid to flush away all of the toxins, so they get laid down as plaques or concretions wherever they can cling. This tends to be in the brain, the kidneys and the joints. This can cause confusion and sometimes bizarre behaviours are noticed if the tortoise is having problems with its kidneys, or its joints may swell. The other problem, kidney stones, is of course self perpetuating, as they prevent proper kidney function. A major cause of kidney stone formation is that the tortoise is kept at too low a temperature. This causes the kidneys to let uric acid settle out of the urine and cause stones. Tortoises do not have very fluid urine like other animals, but excrete urates in an almost solid form. There is not far to go from this crystalline substance to a kidney stone and so if the tortoise becomes dehydrated, it can be serious very quickly.
What to watch out for
Tortoises with kidney disease are often sluggish and clearly generally unwell. Toxins build up in the blood and every organ in the body has to work overtime. Legs can become swollen as fluid balancing goes wrong, but while fluid can gather in the extremities, it is sometimes in short supply in the rest of the body, leading to heart and brain problems. Most cases of tortoise lethargy is attributable to a simple and obvious cause, such as a problem with ulcerative stomatitis (mouth rot) or an infestation of worms, mites or ticks making the animal anaemic. But if on examination nothing obvious is apparent, the vet will test for kidney function. This can be an x-ray, blood tests, urine tests or a combination. Sadly, if the kidneys are seriously impaired there is generally no successful treatment, although dietary measures can prolong life for a while. It is unlikely that a tortoise which has renal problems will survive a hibernation, as this is in itself a big strain on the kidneys, even if they are healthy.
Prevention of renal problems in tortoises
Good husbandry is the answer, with special emphasis on temperatures and diet. The tortoise needs a minimum temperature to be able to metabolise food properly and if this is not maintained, toxins will rise in solution in the body fluids and in time this will put huge pressure on the kidneys. If for some reason temperatures cannot be maintained at the suitable level, food should be fed very sparingly, so that this pressure does not occur. The tortoise will not suffer for a short period, as long as water is available, and possibly permanent and fatal kidney damage will be prevented. There is a very common old wives’ tale that tortoises do not drink as they get all their liquid needs from their food. This is not so, although some tortoises do not seem to drink much. If you wash leaves and other food and do not shake the water off, this makes their intake higher, but water must always be available. Some tortoises like to soak themselves in their water dish. If they do this, they may defecate in the water, so it is essential that this is monitored and kept clean.
Some tortoises awake from hibernation very dehydrated and this can put enormous pressure on the kidneys. A tortoise should ideally have a vet look it over before being encouraged to hibernate and also should not be allowed to sleep too long; three months is usually enough. If you do wake it up you must provide heat so that it does not go back to sleep again. Being interrupted in hibernation is very dangerous, as the metabolic systems do not always go back into hibernation mode and without the very low metabolic speed which is achieved with first hibernation taking place, a lot of damage can be done to the body, especially the kidneys.
If you think that your tortoise is withholding fluid elimination because it is dehydrated and the weather is warm enough, you could try lightly misting it with the hose. In the wild, tortoises often only urinate when it is raining, as that is the time when they know they can replace the lost fluid. This is not a sure fire answer to what can be a serious problem, but in any case, the tortoise will probably appreciate a shower.