Gradual decline in functional capacity of organs from maturity.
Different body systems age at different rates older animals must be assessed as individuals, using functional changes in body systems rather than chronological age.
Metabolic effects
Activity does not decrease markedly after maturity.
Lean body mass does not decrease much with age.
Maintenance energy requirements do not decrease with age.
Protein digestion decreases with age.
Fat digestion often decreases with age.
Skin
Decreasing elasticity/pliability due to increased calcium and pseudoelastin; decreased moisture.
May be concurrent hyperkeratosis with follicular atrophy and hyperpigmentation.
Increasing incidence of skin neoplasia .
Alimentary
Dental calculus .
Peridontal disease .
Loss of teeth.
Decline in the amount of functional salivary tissue.
Increased risk of constipation due to inactivity.
Urinary
Renal failure - major cause of death in older cats can cause:
Reduced assimilation and use of nutrients (decreased caloric and nutrient intake, intestinal malabsorption ).
Weight decrease, muscle wasting.
Increasing accumulation of metabolic waste products, especially urea.
Calcium oxalate urolithiasis - increased risk in older cats:
Hematuria .
Crystals in urine .
Acidic urine .
Musculoskeletal
Arthritis is common which may reduce the ability and desire to eat.
Control body weight to minimize discomfort.
Cardiovascular
Cardiac insufficiency can occur but does not seem to be as frequent as in dogs.
Special senses
Decreased vision and hearing .
Behavioral
Degenerative disease and geriatric changes decreased desire to eat.
Diabetes mellitus increased or decreased appetite. Depression or pathological mourning can occur due to the loss of a companion and can cause anorexia.
Introduction of another pet changed eating pattern (social facilitation increasing, intimidation decreasing).
Changes in daily routine of geriatric depression, changed eating pattern.
Switch to senior diet (if indicated in individual cat) containing:
Less fat, fewer calories.
Normal fiber level to avoid constipation
Easy to chew kibbles to avoid aggravation of dental disease. Canned diet may be necessary; lacks the abrasive cleansing effect of dry food but increases fluid intake.
Normal protein levels to maintain lean body mass.
Less phosphorus and sodium.
Quantities
Feed to maintain lean body mass.
Frequency
As cats age, they may not be able to maintain body condition on free choice.
older animals must be assessed as individuals, using functional changes in body systems rather than chronological age. 
