We can make several observations about ageing changes:

  1. they are progressive
  2. they are irreversible
  3. multiple organ systems are involved
  4. physiological mechanisms ultimately become impaired
  5. variable expression is shown between individuals.

Ageing changes that may occur in tissues include:

The pigment lipofuscin is deposited in body tissues in increasing amounts with increasing age, indeed it has been called 'the pigment of ageing'. In the dog lipofuscin is deposited at five times the rate that it is in humans.

Ageing changes proceed at varying rates in different organ systems of the body, and may be present in varying degrees of severity between individuals of the same age. Typically, older animals lose sensitivity of their major senses, e.g. vision, hearing, taste and smell, and all organ systems may be affected to some degree by age-related changes.

Geriatric screening is helpful in determining whether or not organ function is impaired, particularly before elective procedures such as minor surgery. Some organ systems are more likely to be affected than others, for example with increasing age teeth are likely to demonstrate:

By the time they are 7-8 years of age 95% of dogs are said to be affected by periodontal disease (Harvey 1988).

The occurrence of obesity increases with age probably due to:

  1. reduced lean body mass (hence reduced basal energy requirement (BER))
  2. reduced exercise
  3. overnutrition.

Obesity can have serious effects on other body systems, e.g. cardiovascular and skeletal systems, and may have a role in the cause of some diseases, e.g. diabetes mellitus.

Some age-related changes that may be seen in various organ systems are listed below (after Mosier and others):

Gastrointestinal tract





Endocrine system

Skeletal system

Central nervous system

Peripheral nervous system

Respiratory system

Immune system


These types of age-related changes may impair normal physiological activities, reduce the ability of the animal to respond to stresses, infections or other attacks on the body, and delay healing processes. Nevertheless advanced age is not regarded as being a disease state.

Because of reduced hepatic function, renal function and suboptimal metabolic processes older animals may have an impaired ability to metabolise and excrete drugs. Hence medications may need to be given at different dose rates from the normal adult dose. There may also be addirisks associated with general anaesthesia or elective surgery.