For any individual, energy requirements may stay the same, increase or decrease with
advancing age. There are few studies looking at the energy needs of large numbers
of old cats and dogs.
With advancing age a fall in basal metabolic rate has been recorded in humans and
experimental animals. This is thought to be due to a change in the ratio between
lean body mass and fat, there being an increasing tendency to lay down body fat with
advancing age. There are several possible explanations for this trend:
reduced thyroid hormone activity (secretion or receptor response)
other hormonal effects, e.g. sex hormones, catecholamines.
Similar effects may also be seen in dogs and cats. Certainly there is an increased
incidence of obesity in dogs with increasing age (Edney & Smith, 1986).
Energy requirements may also be reduced if an individual is doing less exercise due
to changed behavioural patterns or secondary to other problems, e.g. an orthopaedic problem
such as degenerative joint disease or osteoarthritis.
Older animals with reduced energy requirements should have their energy intake reduced
otherwise obesity may result. Regular weighing of older animals should be recommended
to detect any trend towards weight gain.
Obesity should be regarded as a serious problem in older cats and dogs. Obese animals
have reduced glucose tolerance and hyperinsulinaemia (Mattheeuws et
al. 1984a; Mattheeuws et al. 1984b) even in the absence of frank
evidence of diabetes mellitus. Gross obesity can significantly reduce cardiovascular
and respiratory function and also exacerbates numerous other problems such as skin
disorders, and orthopaedic problems. Obesity in cats is a risk factor for the development
of hepatic lipidosis and in cats and dogs it is a risk factor for the development
of diabetes mellitus.
Most major organ system diseases seen in older animals (e.g. cardiac disease, renal
disease, hepatic disease and neoplasia) result in catabolism and weight loss. This
is particularly important in cats which, because of their high protein-calorie requirement
rapidly break down their own body muscle and other available proteins in the presence
of inadequate protein intake or excessive energy utilisation. Almost all chronic
diseases in the cat result in significant weight loss or even cachexia.
When energy intake does not meet requirements additional energy should be provided
and the selection of energy source (fat, protein or carbohydrates) will depend upon
the underlying clinical status of the animal. In cats protein is a major provider of energy
because of their obligate carnivorous nature, however fat provides 2.25 times more
energy than either protein or carbohydrate and so this will often be the high energy
source of choice for both cats and dogs. Carbohydrate will be used when high protein
or fat intake is contraindicated in the individual because of the presence of impaired
organ function or disease (e.g. renal failure, hyperlipidaemia).