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What Is Crude Protein?


Crude protein, or “protein” to use the abbreviated term, is listed by law on the label of all pet foods, but is it a useful measurement?

Firstly, we need to understand what substances are included under the name “crude protein”. Protein is the collective name for amino acids, which can be better described as “the building blocks of cells”. When it comes to feeding dogs and cats, there are 22 different amino acids required, 10 of which are classified as being essential, while the other 12 are classified as being non-essential. The critical distinction between the two classes is that essential amino acids must be contained in the food if the animal is to survive and grow, whereas the non-essential amino acids can be synthesised in the body from the existing essential amino acids.

Crude protein is an analysis technique that was developed at the Weende Experiment Station by Messrs Henneberg and Stohmann in 1860 and is a part of a broader analytical process that was designed to classify different animal feed-stuffs. The crude protein test is the chemical determination of the nitrogen content of the food, which is then multiplied by a factor of 6.25, with the resultant figure being the assumed percentage of crude protein in the food.

While this method may have been useful in the 1860s, advances in science and nutrition have given rise to a far better understanding of the nutrients required by our dogs and cats (and for all the other animals we keep, for that matter). But worse than that, the assumption that protein contains 16% nitrogen (hence the 6.25 multiplier factor) is flawed in that the nitrogen content varies according to the different amino acids that are present in the food. The critical distinction here is to understand that each different protein source, for example, meat as compared to fish, will have a different amino acid profile, and as the amino acid profile changes so too do the nitrogen content. Furthermore, foods also contain non-protein nitrogen, which is also included in the results of the Weende nitrogen analysis. Non-protein nitrogen is usually around 10% of the total nitrogen content of a food (but varies from ingredient to ingredient), which means the actual protein content of the food will on average be 10% less than the amount suggested by the crude protein analysis.

While this method may have been useful in the 1860s, advances in science and nutrition have given rise to a far better understanding.

From the animal’s point of view, protein synthesis in the body cannot be completed unless the full spectrum of essential amino acids is present in the food. The difficulty here is that the ratio of amino acids required vary between species, and within any species between gender, the stage of development or age, and in an ideal situation on other factors as well. Furthermore, no single protein source provides the required complete amino acid profile for the dog or cat, which means a balanced food must always be made up of a variety of protein sources to ensure all the essential elements are included.

So, what does all this mean when it comes to comparing one food to the next?

Only this; making nutritional decisions based on the crude protein content of different foods is about as useless as suggesting the performance of Henry Ford’s famous T Model is the same as a Formula 1 race car because they both have four wheels and an engine.

The confusion and consequent damage caused by regulating authorities demanding that crude protein is listed on the label can best be illustrated by the 2008 scandal in China relating to infant formula being contaminated with melamine. Contaminated infant formula is credited with having led to the death of 6 babies from kidney stones, and kidney damage, while an estimated 54,000 of the 300,000 victim babies were hospitalised.

Melamine is a type of plastic that is a rich source of nitrogen, and when added to food increases the non-protein nitrogen level of the food and subsequently, the calculated crude protein level. Urea, a nitrogenous fertiliser, is also a useful source of non-protein nitrogen and has commonly been added to animal feed in the past in an attempt to make the feed appear to be of better value through a higher crude protein test. Sadly, both melamine and urea are toxic for monogastric animals, and for this reason, are banned from inclusion in foodstuffs. Even so, this has not prevented some manufacturers from adding non-protein nitrogen additives to their products as the China example illustrates. But, this does highlight the folly of using crude protein as a measurement with which to classify the value of a particular food or product.

….. as useless as suggesting the performance of Henry Ford’s famous T Model is the same as a Formula 1 race car because they both have four wheels and an engine.

As mentioned earlier, the body’s use of protein (or protein synthesis) relies on the supply of a complete and balanced ratio of essential amino acids. Conversely, an unbalanced food that has a high crude protein content will cause synthesis to be interrupted, with a subsequent reduction in growth, health and well-being. The ramification of this, of course, is that a lower crude protein food containing a balanced supply of amino acids will outperform the higher protein food containing the imbalance of amino acids. Furthermore, the addition of a short supplied or missing amino acid to balance out the protein will make a world of difference to the performance of the food and the health of the animal but won’t be reflected by a substantial increase in the quantity of crude protein (nitrogen).

All in all, this makes the pet owner’s task of selecting the right food for their pet a difficult one, and if we can’t use the crude protein level listed on the label as a reliable guide, what can we use on which to base our purchasing decisions?

Fortunately, there are other indications, albeit more obscure, but an indication nevertheless:

Read the label carefully – does the manufacturer make strong claims relating to health and performance, or use very general terms to describe the food.

Check that the ingredient list is diverse – for the food to be genuinely nutritious the ingredients in the food must also be sympathetic to the needs of the gut microbial population (the microbiome). The diversity of life in the microbiome is far more abundant than that found in a rain-forest, with over a trillion creatures from over a thousand species being required for the efficient processing and extraction of nutrients from the food. Without a healthy microbiome, your pet will be unable to unlock the nutrients that are contained in the food.

Ensure the manufacturer’s advertising focuses on the whole food – all too often; we see health claims being attributed to one or two ingredients only. Remember, it is the total nutrient balance that is important; all nutrients are required in the body proportionally to one another, and no nutrient works in isolation to the others.

Check the crude protein level – while we have established beyond doubt the shortcomings of this measurement, it still offers some indication as to the quality of the food when considered in conjunction with the points listed above. Protein tends to be a high-cost component of the food, so manufacturers will usually try to keep their costs down by not including any more protein than is necessary regardless of the amino acid balance.

Ask around – seek advice as to the well-being of other’s pets. When you are out walking and see a particularly healthy and active dog, ask the owner what food they are feeding. Check your breeds social media page – most breeds have a Facebook owners page where information and views can be exchanged.

Contact the manufacturer and ask to speak with their nutritionist – salespeople tend to tell you what you want to hear, whereas nutritionists tend to be more interested in the well-being of the animal. Most nutritionists are passionate about the subject and can be an excellent source of information and tips regarding pet health and welfare.

And last, but by no means least, try the food and monitor the results for yourself – as the old adage tells us “the proof of the pudding is in the eating”, and your pet’s food is no different. But remember, it takes about three months for blood nutrient levels to stabilise when changes are made to the diet, so this assessment technique is one that must be approached in a careful and open-minded manner.
We hope you have found this article of some benefit in fostering a greater understanding of the intricate world of dog and cat nutrition.

Should you require additional information or would like to comment on any of the above, please email us at or

Bill Wiadowski 

Watch Bill discuss and answer questions on Pet Nutrition on our YouTube Channel. 

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