While not a nutrient, energy is required by all animals. Energy is usually expressed in units called calories or kilocalories (1,000 calories usually abbreviated as kcals). An animal gets energy when it ingests food and breaks it down into simpler compounds, which provide fuel to the cells in the body and thus the "energy" to live, thrive, and survive. In a way, it is similar to a fire. When wood is burned in a fire all the energy is immediately released in the form of light and heat. When ingested food is metabolized, some energy is released in the form of heat (that's what allows dogs and cats to maintain a constant body temperature), some is utilized to perform work (moving the body, producing milk, or shivering if the outside environment is cold) and some is stored in the body in the form of fat. The fat can then be broken down at a later time, when needed. Three classes of nutrients found in pet foods supply energy: carbohydrates, fats, and proteins. For pet foods, two of the three energy-yielding nutrients, protein and carbohydrates, contain the same amount of metabolizable or usable energy, about 1,590 kcals per pound. In contrast, fat has more than twice the amount of usable energy, or 3,860 kcals per pound. Usable energy is a key point because sometimes different terms are compared.

Gross energy is the amount of energy a food contains, while digestible energy is the amount of energy that is digested by the dog or cat. For example, wood contains gross energy as evidenced by the light and heat released when it is burned; but since it is not digestible it contains no digestible energy. The difference between digestible energy and metabolizable energy is primarily the amount of energy lost in the urine as a result of the breakdown of protein. Therefore, the only true measurement of energy for animals is metabolizable energy sometimes abbreviated as ME. Using a dry premium pet food as an example the various energy systems are shown below:

Gross Energy ====> Digestible Energy ====> Metabolizable Energy  

2,130 kcal/lb ====> 1,910 kcal/lb======> 1,770 kcal/lb

The energy requirements of adult dog and cats shown on the following two charts. As you can see, as a dog ages their energy requirements decline. There is variation between dogs, so these requirements need to be adjusted to account for these differences on an individual basis. However, since there is no effective relationship between age and caloric intake in cats, the second chart is used as an acceptable guideline for a relationship between weight and energy requirements.

Energy Requirements of a Normally Active Adult Dog*

• * - Based on the following papers
• Finke , MD. 1994. Energy requirements of adult female beagles. Journal of Nutrition 124: 2604S-2608S.
• Finke , MD. 1991. Evaluation of the energy requirements of adult kennel dogs. Journal of Nutrition 121:S22-S28

Energy Requirements of a Normal Adult Cat*

*Although there is no "official" chart for cats due to the fact that there is no effective relationship between age and caloric intake, like there is with dogs, this chart is a fair representation of the energy requirements of a normally active adult cat in relation to weight. For more information, please see the Ever Wonder section on true feeding costs.

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