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Old 03-27-2007, 02:22 PM   #1
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Default How to: Estimate the Calories in Dog Food

First, Im an interested dog owner, sharing what Ive been learning about canine nutrition. I am not a nutritionist, nor a veterinarian, nor am I in veterinary school. Nothing I am telling you should be considered a substitute for the advice of a competent canine nutritionist or veterinarian. Consider this a jumping off point for your own learning.

One of the ways to compare dog foods is by using the Guaranteed Nutritional Analysis on the label to compare key nutrients. Part of the label is the proximate analysis of crude protein, fat, fiber, ash and moisture. Proximate analysis gives you the information you need to estimate the calorie content of the food, and to compare two foods with different moisture content. With this information, you can compare two different dry foods, or a dry food and a canned food, and see how they match up.

Were going to use the food Ive been feeding my hounds (My Food) as our example. The nutritional values listed on the label are:
Crude Protein 30%
Crude Fat 20%
Crude Fiber 4%
Moisture 12%

From these numbers, we can estimate the percentage of carbohydrates in the food. The listed percentages add up to 66%. From this, we can estimate that carbohydrates make up the remaining 34% (100-66).

The caloric content of the food comes from the protein, fat and carbohydrates. We can estimate the caloric content by remembering two numbers. The calories per gram of protein and carbohydrates is about the same. Fat contributes a little more than twice that. The University of California at Davis School of Veterinary Medicine recommends estimating 3.5 kcal per gram of protein and carbohydrates, and 8.5 kcal per gram of fat. Other nutritionists recommend estimating 4 kcal per gram of protein and carbohydrates, and 9 kcal per gram of fat. A half kilocalorie per gram doesnt seem like much of a difference, but it adds up. Because I dont have an easy way of determining the scientifically-measured digestibility of the food, I prefer to use the lower, more conservative estimate and round to the nearest whole kilocalorie.

Using our example, the kilocalories from protein are 105 kcal per 100 grams (30 x 3.5). The kilocalories from carbohydrates are 119 kcal per 100 grams (34 x 3.5). The kilocalories from fat are 170 kcal per 100 grams (20 x 8.5). The total estimated calories from 100 grams of this food are 394 kcal per 100 grams. I measure the food I feed by volume, not weight, so I need to weigh a measure of food. I use a one-cup measure to portion the food, so I weighed a cup of the food in grams, and found that one cup weighs 115 grams. That means one cup of my food contains about 453 calories. If I want to, at this point I can also calculate the percentage of calories from protein, fat and carbohydrates.

I am considering switching to another food, higher in quality of ingredients, but lower in protein and fat. The other food also has a different moisture content, so I need to standardize the proximate analysis for each food by calculating the content of each food on a dry matter basis. The dry matter basis removes moisture from the equation. Canned foods contain much more moisture than dry foods. Looking at the nutritional values on a dry matter basis allows you to compare two different foods. In my case, Im looking at two dry foods.

The nutritional values for the other food are:
Crude Protein 28%
Crude Fat 12%
Crude Fiber 4%
Moisture 10%

If a cup of the other food weights 120 grams, how many calories per cup does the other food contain? (The answer is 433 kcal per cup).

To convert the nutritional information to a dry matter basis, we have to determine the dry matter content of the food the total content less the moisture. The dry matter content of my food is 88% (100%-12%). The dry matter content of the other food is 90% (100%-10%). To compare the values on a dry matter basis, I divide the values from the labels by the dry matter percentage.

The dry-matter nutritional values of my food are:
Crude Protein 34% (30/.88)
Crude Fat 23% (20/.88)
Crude Fiber 5% (4/.88)
Carbohydrate 39% (34/.88)

The dry-matter nutritional values of the other food are:
Crude Protein 32% (28/.9)
Crude Fat 14% (12/.9)
Crude Fiber 5% (4/.9)
Carbohydrate 52% (46/.9)

Evaluating a canned food on the dry-matter basis is very important, because once the body removes the moisture from the food, the nutritional balance of the remaining dry matter is very different from what appears on the can label. A can might contain 78% moisture, leaving only 22% dry matter, so the percentage of protein in the dry matter might be much higher than the percentage of protein in the can, and may be significantly higher than the dry food you are feeding.

Remember that these are estimates, only, and not precise calculations of the number of calories in the food. Still, this gives you a starting point for determining how much to feed your dog, and a means for comparing two different foods.
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Old 03-27-2007, 03:48 PM   #2
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Thanks so much for this great post! Very valuable info!
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