Feeding

Feeding Strategies

Caloric Energy Measures in Dog Food

The energy content of dog foods is one way to compare brands. However, it also causes much confusion because not every brand uses the same methods to express its energy content.

The first problem in the expression of kilocalories is in volume. Many brands express energy content in kilocalories per cup. This is a poor way to compare dog foods because it is too vague. A cup can be many sizes, and even if we use the standard 8oz liquid measure it is misleading. Since dog foods vary greatly in density and size of kibble, a denser kibble will look like it has a lot more calories than a less dense one. A more accurate way is to compare a given weight of the foods such as kilocalories per pound or kilogram.

Beyond unit measures, there are also different ways to measure the actual caloric content of a given mass of food. They are Gross Energy, Digestible Energy, and Metabolizable Energy. It's important to understand the differences so you can make better comparisons

Gross Energy

Gross energy is the simplest measure and as such is the least accurate. It is measured by the complete oxidation of the food in a bomb calorimeter. The energy measured is the heat released. The problem with this measure is that not all of the combustible energy in a food is available to the dog for metabolism. Energy is lost in digestion, urine, feces, and other processes in the dog's body.

Digestible Energy

This method is an improvement over gross energy because it takes into account energy lost in digestion and feces. It still does not account for urine loss so it is still an incomplete measure of a food's energy available to a dog.

Metabolizable Energy

M.E. is the best measure of dog foods we have available because it takes into account all of the factors listed above. It most closely expressed the amount of energy a dog will get from a given amount of food.

However, ME cannot be measured by a lab test, and since ME data is not available on the individual ingredients, the ME value must be estimated using the following equation:

M.E. Kcal/gram = (.035 * (%protein + %carbohydrate)) + (.085 * %fat)

Since carbohydrate content is not listed on dog food labels we must calculate it ourselves.

%carbohydrate = 100 - %protein - %fat - %fiber - %moisture - %ash

Ash is one of those terms that sounds worse than it is. It is basically the "none of the above" category in dog food. It is the non-combustible ingredients of the food and is composed mainly of minerals. High quality performance dog foods typically fall in the 7-9% range for ash. There is no clinical relationship between ash content and disease in dogs, however, high ash content foods may indicate a compromise in quality. Thus, when comparing dog foods it is important to look at the ash content. You will generally have to ask for that information because it is not usually listed on labels.

To convert the KCal/gram into pounds multiply the result of the ME calculation by 454.

So as an example, lets assume we're looking at a food with 32% protein, 20% fat, 3% fiber, 10% moisture, and 7% ash. That leaves 28% as carbohydrate. If we plug those numbers into the equation we get:

ME Kcal/g = (.035 * (32 + 28)) + (.085 * 20) = 2.1 + 1.7 = 3.8

Me Kcal/lb = 3.8 * 454 = 1725.2

In summary, M.E. is the best measure to use in comparing the energy content of dog foods. Any respectable company should be able to provide this figure for you, just make sure you keep your measure the same (grams vs. lbs.) for even comparison.