Are You Comparing Apples With Oranges?
Any pet owner that recognises the important role nutrition plays in keeping their pet as healthy as possible will be used to checking the ingredients list and nutritional data on the pet food label. The information on the label provides the ingredients contained in the pet food, and the percentage of various analytical constituents in the pet food such as protein, fat, fibre and ash. Whilst this is a good start, on its own this data might not tell you everything you need to know about the food to make a meaningful comparison between one pet food and another.
So when you compare a wet food (or raw food for that matter) with dry food, it is important to: (1) check that the analytical constituents are provided on an as fed basis and (2) convert it to a dry matter basis to make a meaningful comparison.
The analytical constituent of a pet food is the analysis of a food’s protein, fat, fibre, ash, and moisture content. Some brands choose to provide further information such as the omega oil, or calcium and phosphorus content of the food, however, this is not a legal requirement. The amount of each of these nutrients is represented by a percentage, allowing you to determine which foods have higher or lower levels of nutrients compared to others. Depending on whether the percentages are expressed as a typical analysis, or, guaranteed analysis, the accuracy of the figures can differ. Amounts given as a guaranteed analysis will provide the minimum amounts of protein and fats, and the maximum amounts of fibre, moisture, and ash.
To be able to provide maximum and minimum amounts required for a guaranteed analysis, the pet food manufacturer must conduct multiple nutritional tests of its food many times to create a wide range of data. This data then allows them to calculate the maximum and minimum percentages of each analytical constituent using standard deviation.
Typical analysis is the average amount of nutrients in a pet food. These percentages are not as accurate as those calculated for the guaranteed analysis, and the actual percentage could be considerably different to the one stated on the label (although they might be preferable when considering protein and fats which are only expressed as minimum percentages under the guaranteed analysis). The European Pet Food Industry has a “Code of Good Labelling Practice for Pet Food” and it states the allowed tolerances for the percentages stated on the typical analysis of the analytical constituents.1 These tolerances differ from nutrient to nutrient, but typically range from less than 1% up to 8%.
Therefore, when comparing pet foods, it is important to be aware of the type of analysis represented on the pet food label as well as whether the percentage is expressed on a dry matter basis, or, an as fed basis.
Once you have identified whether you are comparing a wet food with a dry food based on a guaranteed analysis, or, a typical analysis, and you have ensured that you are using the same analysis for both foods, you can then convert the wet pet food to a dry matter basis. To assist you with this we have provided an example below.
Going back to our earlier example of having a dry food with a dry matter analysis of 30% protein, and a wet food with an “as fed” analysis of 10% protein and 75% moisture, it appears that the dry food contains significantly higher levels of protein. However, if the wet food is analysed on a dry matter basis, the protein content in the wet food is actually 40%. The formula used is as follows:2
Percentage of Nutrient (in this case protein)
Percentage of Dry Matter (calculated by 100 – moisture percentage) x 100
The percentage of the protein is 10% which should be divided by the percentage of dry matter in the food (which is calculated by taking the percentage of moisture from 100, which in this case is 100 – 75% moisture = 25%).
So we have 10 ÷ 25 = 0.4 x 100 = 40% crude protein.
So now you have a meaningful comparison between dry and wet foods and can make a decision on the protein content of your pet’s food. This formula can also be used to calculate the dry matter analysis of any “as fed” nutrient such as crude fibre or fat, which will help you obtain a more accurate picture of the true analytical constituent of your pet’s food. This can be especially useful when changing your pet’s diet due to a medical condition such as pancreatitis, where it is important to understand the fat and fibre content of your pet’s foods.
Many brands in the UK choose to display the analytical constituents on their wet foods on an “as fed” basis, however, if you do not know the format in which they have displayed the data it is best to contact the manufacturer directly to find out. Further, in the UK there is no legal requirement to provide a guaranteed analysis, and many brands do not provide this information, those that do include ZiwiPeak and Orijen. These brands are sold in the US where the guaranteed analysis must be provided by law.
At Thoughtful Pets, we know from talking to customers that there is much confusion over whether the analytical constituents are expressed on a dry matter basis or an as fed basis, and whether the analysis is guaranteed or typical, and what variations are permitted for each analytical constituent. Accordingly, we are making a commitment to you, our customers, to provide this information. Over the next few months you will find this information appearing in the “More Information” tab of all relevant products on our website, where we will provide the comparison on a dry matter basis and explain whether the analysis is typical or guaranteed and what variations are tolerated under the FEDIAF “Code of Good Labelling Practice for Pet Food”.Back