The Effects of Aging on Cats
Dr. Nicholas Dodman
Like us, cats don't stay young forever - they age. While some aspects of getting old may not be much fun, getting old is not all bad. Each stage of life has its joys, pleasures and drawbacks. Middle age for a cat, which is between 8 and 10 years of age, is a kind of gray zone during which the cat is busily engaged in the process of life without any particular physical or mental deterioration to hamper him. But somewhere towards the end of middle age, cats start acting and feeling their age. The Kidneys. Kidney function is often impaired in old age. With advancing age, blood flow to the kidneys decreases, there is a loss of filtering cells (nephrons), and impairment in resorptive processes in the nephrons. The result of all this is a failure of the kidneys to concentrate urine, so that older cats with this type of deterioration will necessarily have to drink more and, consequently, produce a larger amounts of more dilute urine. It is extremely important to make sure that such cats have constant access to water so that they do not go into kidney failure. Some special kidney diets that contain low quantities of high quality protein can help sustain cats in the borderline kidney failure.
The effects of the aging process are both physical and mental. Physically, structural and functional changes occur in virtually all organ systems throughout the body, affecting vision, hearing, stamina, susceptibility to drugs and locomotor activity. Mental changes are secondary to decreasing brain size and a reduced number of brain cells. In some cases, feline Alzheimer-like changes hasten deterioration. Aging does not affect all cats in precisely the same way. Some cat breeds, and some individuals, are more successful agers than others. Some cats, at the age of 14 years, may have no noticeable physical or mental incapacitation. Others of the same age, however, are already handicapped by age-related internal organ failure, failing senses or orthopedic problems.
Age-Related Physical Changes
The Liver. Although some tests of liver function show progressive deterioration with age, most cats survive to a ripe old age without this progressive loss affecting them in any noticeable way. However, in some cats, fat accumulation occurs in the liver (sometimes secondary to other diseases such as diabetes) and this can result in an increased size of the liver with increased levels of liver enzymes in the blood. Liver cirrhosis is also a disease of the older cat because of its chronic and progressive nature.
Thyroid Glands. Hyperthyroidism has been reported to be one of the most common endocrine disease in the cat. Hyperthyroidism will cause a dry lusterless coat, weight loss and an increased appetite, to name but a few of the clinical signs.
Adrenal Glands. The adrenal glands, that produce various hormones involved in the regulation of blood sugar, electrolytes, stress regulation, and many other functions, are affected in various ways by the aging process. Adrenal exhaustion has been described in elderly patients undergoing continued stress but the opposite, hyperadrenicorticism, can occur in middle aged and older cats. The latter causes signs such as muscle weakness, potbelly, hair loss, increased thirst, and increased urine production. If hyperadrenocorticism is diagnosed, it can be treated.
Pancreas. Diabetes mellitus (sugar diabetes) is usually a disease of the older cat. Complications associated with this disease include increased thirst and urine output, muscle wasting, and liver disease. This type of diabetes can be controlled using dietary control and insulin.
Musculoskeletal System. While young cats appear strong, well-muscled and can run like the wind, older cats usually show muscle wasting and are often handicapped by arthritis or intervertebral disc disease. Analgesics and, if indicated, various surgical procedures can bring many cats relief
Cardio-respiratory System. As you might expect, both components of the heart and lung system are affected adversely with increasing age. A particularly common cardiac disease of older cats is one in which the heart walls thicken (cardiomyopathy). This condition leads to cardiac murmurs and, functionally, to cardiac insufficiency. Meanwhile, aging changes in the lungs, such as thickening of the walls of the small airways, leads to reduced efficiency of gaseous exchange.
Special Senses. Cats' eyesight becomes poorer as they get older, due to age-related changes in the eye itself and in the processing of visual images centrally. The most common ocular aging change of all, lenticular sclerosis, in which the pupil of the eye appears grayish, does not significantly affect vision at all. Cataracts, however, which are also more common in elderly cats, do impair vision, particularly when the cat is in bright light and his pupils are constricted.
Cats' hearing deteriorates progressively with age so that many older cats appear not to hear you and they do not respond to outside sounds that formerly would have aroused them. Loss of hearing can be either peripheral, due to changes in the ear itself or, as with failure of vision, related to changes in central processing.
Central Nervous System . Cats' brain weight decreases with age primarily because of neuronal death in the cerebral hemispheres. Functionally, there is decreased production and increased destruction of central neurotransmitters.
Behavioral Changes. Because of general central nervous system changes mentioned above, cats progressively slow down mentally as they age. They become less interested in things around them, less reactive to things going on, spend more time sleeping, and tend to walk whereas before they might have run. "Normal" aging changes in cats are not usually incapacitating but merely produce a gradual decline in mental function, which can seem quite appropriate.