What is Crude Protein?

It is calculated based on the food's nitrogen content, since proteins are composed of amino acids, which contain nitrogen. The term "crude" indicates that this measurement does not distinguish among protein types or sources.

Example

A dry cat food bag may list "crude protein: 30%."
This percentage represents the total protein content in the food derived from various ingredients.

Importance of Protein for Cats

Not all proteins are equal. Animal-based proteins (e.g., chicken, fish, egg) are considered higher quality and more digestible for cats than plant-based proteins. Thus, dry cat foods should prioritize animal-based proteins as the primary ingredient.

A study found that some vegetarian cat foods did not meet AAFCO amino acid requirements, highlighting the importance of evaluating protein quality.[2] Another study showed that high-protein foods with phosphorus levels similar to those of lower-protein foods increased uremic toxin levels in cats with reduced kidney function.

Insufficient Protein Intake:

• Muscle wasting and weakness

• Poor coat condition

• Compromised immune function

• Impaired growth in kittens

Excessive Protein Intake:

• High protein levels, especially from low-quality sources, can strain cats' kidneys and liver, potentially causing organ damage over time.

Example

A food with 35-40% crude protein is beneficial for a growing kitten to support rapid growth and development.

Sources of Crude Protein

The quality of crude protein depends on its source. High-quality proteins typically come from animal sources, providing all the essential amino acids cats need. In contrast, plant-based proteins may lack certain amino acids and are less digestible.

• Animal-based Proteins: Chicken, beef, fish, turkey, lamb.

• Plant-based Proteins: Soy, corn gluten meal, pea protein.

Example

A premium dry cat food might list chicken meal (a high-protein source) as the first ingredient, ensuring a higher crude protein quality.

Interpreting Crude Protein in Dry Cat Food

Understanding the percentage of crude protein on a cat food label is crucial, but it's equally important to consider the source and quality of that protein.

Examples

Food A: "Chicken meal, turkey meal, fish meal" - High-quality animal protein sources.
Food B: "Corn gluten meal, soybean meal" - Lower-quality plant-based proteins.

Dry Matter Basis Comparison

To accurately compare protein content across foods, it’s important to convert the "as fed" values to a dry-matter basis, excluding moisture.

The formula for Calculating Dry Matter

The dry matter amount (A) in percentage is calculated using the following formula:

Dry matter % = ("As fed" nutrient % / (100% - Moisture %)) x 100%

For example, if a dry food contains 32% protein and 10% moisture on an "as fed" basis, the dry matter protein would be:

Dry matter protein % = (32% / (100% - 10%)) x 100% = 35.6%

How much Protein?

The Association of American Feed Control Officials (AAFCO) and other organizations provide guidelines on protein content in dry cat food:

Kittens

Adult Cats

Senior Cats

While there is no separate AAFCO profile for senior cats, some research suggests moderately higher protein levels (around 30-35%) from high-quality sources may help preserve lean body mass as cats age. However, cats with kidney disease may require lower protein levels prescribed by a veterinarian.

Bottom Line

Common Questions about Protein

Sources

• PubMed - Study on protein and kidney function

• PubMed - Vegetarian cat food amino acid study

• PubMed - Protein requirements study

• NCBI PMC - Protein research

• Semantic Scholar - Related research

• FEDIAF Nutrition Guidelines

• PFIAA Resources

• VIN - Veterinary Information Network