Dog owners are in search of information about appropriate food choices for their pets. You can turn to family and friends for their recommendations, but keep in mind that what works well for one individual is not always the best choice for another.
Your veterinarian is another good source of information, of course, and so are reputable internet sites like the PetMD Nutrition Center and the MyBowl tool. But don’t overlook something that is probably close at hand: the label covering your dog’s bag of food.
Dog food labels contain a lot of information. The article Demystifying the Dog Food Label provides a good overview of what legally must be included, but doesn’t go into much detail about the guaranteed analysis. Let’s take a closer look at this useful resource.
To begin with, this is what a guaranteed analysis tends to look like:
This example provides significantly more information than many pet food labels do. By law, all a manufacturer has to report are the minimum amounts of protein and fat and the maximum amounts of water (moisture) and fiber that are in the diet. Including information about vitamin, mineral, and essential fatty acid levels is an added bonus.
But the raw data from the guaranteed analysis only gets you so far. To compare different dog foods that contain very different amounts of water (e.g., canned and dry formulations), as well as evaluating how a particular food measures up to the nutrient levels for dogs recommended in the MyBowl tool, you’ll need to compensate for the "dilution" caused by the moisture in the food. This requires a little math. (Have no fear, the calculations aren’t too tough!)
First, find the percent moisture that is reported in the guaranteed analysis, and subtract that number from 100. This is the percent dry matter for the food. Next divide the nutrient percentage on the label that you are interested in by the percent dry matter for the food and multiply by 100. The resulting number is the nutrient percentage on a dry matter basis. For example, if a label lists the crude protein minimum at 21% and the moisture maximum at 10%, the calculations would be as follows:
100-10=90 and then 21/90 x 100 = 23% protein on a dry matter basis
So with a small investment of time and brain power, you now have some very useful information about whether or not a food provides properly balanced nutrition for your dog. And it all came right off the bag (or can) itself!
Dr. Jennifer Coates
Image: brian hefele / via Flickr