Energy needs of companion animals: matching food intakes to requirements throughout the life cycle.

An animal's primary demand from its diet is for energy. Unlike an individual nutrient, there is no range of acceptable intakes, but rather a specific energy requirement for a given set of conditions. Accurate assessments of both food energy density and the energy needs of the animal are implicit in providing reliable feeding recommendations. The metabolizable energy content of a food is best measured using in vivo testing in the target species. However, the demands of biological testing mean that a set of factors is desirable to provide reasonable estimates. Assessment of energy requirement in dogs is confounded by their wide range of body weights. It should be expressed on an allometric basis, but the precise value for the exponent is still a matter of some debate. For cats recent studies suggest there may be an allometric relationship over a weight range of 2.5-6.5 kg. Energy requirement is dependent on a number of other factors, in particular, activity, environmental temperature and life stage. Demand increases most in lactation (four times) and growth (up to three times). Old animals show a decline in energy requirement, but this may reflect principally a decrease in activity, rather than any underlying change in metabolism.