Chronic kidney disease (CKD) – sometimes also referred to as chronic renal failure - is an irreversible and progressive condition involving structural and functional abnormalities of one or of both kidneys.

Healthy kidneys have several vital functions; they are responsible for:

• eliminating waste products from the body
• maintaining the body’s fluid balance
• regulating and filtering minerals from the blood
• producing hormones that help regulate blood pressure, stimulate the production of red blood cells, and control the calcium metabolism which is important for healthy bones.

Due to the structural damage to the kidney, the organ’s ability to perform the above-mentioned functions becomes incrementally compromised. Kidneys have a sophisticated filtering system consisting of thousands of microscopic tubes and a network of small blood vessels that together form the structural and functional units of kidneys called nephrons. When some of these nephrons get permanently damaged, the loss of function can still be compensated by the remaining tubes for some time. However, when the disease progresses to a level where more than 70% of the kidneys are affected, compensation does not work anymore, and the organ functions fail completely;  blood is no longer properly filtered, leading to the accumulation of dangerous amounts of waste products and fluid inside the body, which eventually causes death.

Kidney failure can either be the final stage of a slowly progressing decline in function (chronic kidney disease) or happen suddenly (acute kidney failure). Acute kidney failure – also referred to as acute kidney injury – can result from direct trauma to the kidney, lack of blood flow to the kidneys (due to heart failure or dehydration), toxins or infectious diseases; it is usually developing over a matter of days or weeks and may affect cats of all ages.

Chronic kidney disease, in contrast, develops gradually over months to years. Though it is mostly considered to be a disease of  senior animals, it may occur, in fact, in cats of all ages with varying frequency.

Kidney failure can affect both free-ranging big cats as well as those in captivity, but it appears to be much more common in the latter. However, it needs to be taken into account that there is much more diagnostic data available from big cats in captivity than from those in the wild.

One factor that is most likely contributing to the supposedly  higher prevalence of CKD in captive big cats is their increased life expectancy compared to that of their conspecifics in the wild. In their natural habitat, the average life expectancy of big cats is around 10 to 15 years – depending on the species - whereas under appropriate husbandry conditions (with regular supply of high-quality food and medical care), these animals can reach an age of 20 to 25! Unfortunately, getting older also increases their risk of contracting various diseases including kidney disease. In the wild, felids often die from other causes before certain diseases can manifest.  

At the same time, sadly not all captive big cats are raised and kept in good conditions; many are fed with species-inappropriate unbalanced diets that do not sufficiently resemble their diet in the wild. The protein-heavy diet of free-ranging felids is normally separated by fasting days whereas captive felids often are fed high-protein diets on a daily basis. Diets that are too high in protein and phosphorus are known risk factors for developing chronic kidney disease.

Cats are generally considered to be more susceptible to kidney disease than bears and several other species. The underlying reasons for the higher susceptibility of cats have not yet been fully understood though, and more research needs to be done in this field. 

To date, several risk factors that may lead to CKD in cats have been described in the literature. In domestic cats, there seem to be certain breeds that are more easily affected suggesting a genetic predisposition for the disease. Some studies have indicated that periodontal disease might contribute to the development of CKD. Also, feline-specific viral diseases and other (primary) renal diseases have been associated with CKD. Furthermore, cats are pure carnivores (relying on meat as their sole food source).The resulting  high intake of proteins - particularly if the diet is not properly balanced - may put a strain on the kidneys, which can potentially result in damage over time. Therefore, chronic kidney disease is a common health issue in (big) cats, especially when they get older.

Bears, in contrast, have highly adaptive kidneys. During hibernation, the bear's kidneys reduce their function to a minimum level. Despite the long period of immobilisation without any food or water intake and no excretion of urine during hibernation, the kidneys regain full function in no time after waking up in spring. The effective metabolic mechanisms that render this possible make them less vulnerable to kidney failure - a phenomenon that is investigated by researchers hoping to mimic some of the underlying mechanisms and to identify solutions to human disease. 

During the early stages of the condition, most patients do not show any symptoms at all. When clinical signs become apparent, the disease has usually already reached an advanced stage. One of the first behavioural changes that can be detected in big cats with CKD is frequent drinking/increased water intake and frequent urinating.  

Later on, when the kidney damage progresses further, the animal might be nauseous, suffer from reduced appetite and as a consequence lose weight. They often vomit or have diarrhea, which weakens them further. Other findings include, but are not limited to, muscle wasting, hypothermia, lethargy, hypertension, ulcers (painful sores) on the oral mucosae (the lining of the mouth cavity), and a urine-like odour on the breath. In a final stage, the animal often does not eat or get up anymore.

Unfortunately, chronic kidney disease cannot be cured. Damage inflicted on the structural and functional units of the kidneys is irreversible. Only the progression of the disease can be slowed down.

Therapeutic approaches aim at reducing the build-up of toxic waste products, maintaining hydration, decreasing urinary protein loss, controlling blood pressure, and regulating disturbances in electrolyte concentrations. Measures taken include adaptations to the diet, efforts to increase the intake of fluids, and medication.

Early diagnosis through analysis of urine and blood can thereby significantly improve the management of disease. Therefore, regular health checks are carried out in FOUR PAWS sanctuaries to monitor the health status of the animals, and to provide targeted care and a good quality of life for as long as possible.

Chronic kidney disease often progresses slowly; with proper management, a good quality of life might be maintained for a prolonged period of time reaching from several months up to a few years. The life expectancy is, however, very low if the disease is diagnosed very late and the kidneys are already severely damaged.

Severe clinical signs such as lethargy, appetite loss, weight loss, etc. only appear when the damage has already affected more than 70% of the kidneys’ nephrons (structural and functional units of the kidney). Furthermore, wild animals tend to hide their pain, which makes the detection of diseases through observation very challenging. Once the stage of prominent clinical signs is reached, suitable measures to manage the disease become very limited, and  euthanasia may remain the only option to prevent the animal from suffering.

How long an animal can survive after it has been diagnosed with chronic kidney disease will therefore largely depend on the extent of organ damage, and certainly also on the quality of medical care provided. If the disease is detected at an early stage and suitable measures are taken immediately, animals may still live for some months or years before they might show severe symptoms. This has been the case with our lion Bobby, for instance, who was rescued in 2018 from Safari Park Fier in Albania. He was diagnosed with chronic kidney disease the same year. More than two years after the diagnosis, he is still having a good quality of life in FELIDA Big Cat Sanctuary.

On the other hand, the kidneys of Bobby’s father Zhaku were already severely damaged when the veterinarian examined him for the first time during the rescue mission. Despite the poor prognosis, we still hoped to give Zhaku a good life for quite some time with the help of medication and proper care, but his condition deteriorated so fast that there was nothing we could do for him anymore. We had no other choice than to let him go.

Though chronic kidney disease is mostly considered to be a disease of  senior animals, it may occur in cats of all ages with varying frequency. Sultan and Sayeeda were both rescued in 2017 from a war-torn zoo in Syria and were diagnosed with chronic kidney disease soon after their arrival at our FELIDA Big Cat Sanctuary. Like in most cases of chronic kidney disease, the cause of the illness could not be determined with certainty; contributing factors presumably included malnutrition and lack of proper drinking water during their first years of upbringing, potentially complemented by a genetic predisposition.

Medication and proper care were provided to Sultan and Sayeeda to the highest possible extent until a progressed stage of disease was reached and the animals started to show persistent signs of compromised well-being. When there is no hope for improvement, ending the suffering is the last part of the care we can provide to the animals we rescue.

All animals taken care of by FOUR PAWS – including those that do not suffer from kidney disease – are only put under general anaesthesia if strictly necessary; this could be either for medical reasons or for loading them safely into transport crates, when there has not been any chance yet to train them to walk into the crate. Anaesthesia becomes necessary in most of these cases, since big cats are highly dangerous predators and hence many procedures can only be carried out safely for both the animal and the veterinarian if the cat is anaesthetised. Routine physical examinations such as checking the teeth, paws, eyes, etc. can often be done without anaesthesia through positive reinforcement training, but full examinations of the whole body as well as many treatments can only be done under general anaesthesia.

Before we put an animal under anaesthesia, the veterinarian carefully evaluates the benefits and risks. Measures are taken to limit the strain on the body by keeping the duration as short as possible but as long as necessary and by using anaesthetics that have as few side effects as possible. Also, during anaesthesia the vital parameters of the animals are thoroughly monitored, and the kidney function is supported through receiving intra-venously balanced electrolyte solutions.