Comparing Protein Sources Using Biological Value

If you are just starting out your research in dog nutrition, you may still think that high-protein sources are only quality meat parts such as chicken breast or steak. I am here to surprise you that cattle hooves, bird feathers, poultry beaks, and even poultry feet are also protein-dense sources of protein.

So, are all animal body parts high in protein?

The answer is no. In fact, hair, nails and horns are composed of primarily keratin, which is a protein but not one that provides nutrition to your pet.

What is the difference between quality and quantity when it comes to protein? The term “quality” refers to the amino acid composition of the protein source while the term “quantity” reflects the total amount of protein in the product.

Usable vs non-usable ‘available’ protein:

Pets may be unable to digest and absorb protein available in some protein sources such as in cattle hooves, feathers and beaks.

Usable protein is the amount of protein that your pet’s body can actually use from a food.

Non-usable or unavailable protein is present in all foods but is not digestible or absorbable and therefore, provides no nutrition to your pet.

Dogs are able to digest and absorb more nutrients, including protein, than humans. This is due in part to their shorter intestines and higher stomach acidity.

While the gastrointestinal tract of both species is similar, there are some key differences. For example, the human stomach pH is around 4 while the dog stomach pH is around 6.

This means that dogs are able to digest and absorb more nutrients, including protein, than humans.

I think that makes sense as we’ve all seen dogs trying to very last or ‘hard’ part of that bone. They must ‘know’ they’re getting some nutrients out of them.

Biological Value of Plant vs Animals Protein Sources:

A protein’s BV depends on its amino acid composition, digestibility and absorption. The BV of animal proteins is generally higher than plant proteins because they are more digestible and have a better amino acid composition.

Plants typically contain less of the amino acids that are essential to dogs, such as methionine, cysteine and tryptophan.

Animal proteins are also a more bioavailable source of protein for dogs. This means that they are better able to digest and absorb the nutrients from animal proteins.

Quantifying Protein Value per source:

One way to determine the quality of a protein source is by looking at the protein biological value (PBV).

The PBV is a measure of the percentage of nitrogen from a food that is retained in the body.

A protein with a higher biological value signifies that more of the nitrogen is used by the body for growth and repair, making it a higher quality protein.

In other words, a protein with a PBV of 100 would be considered a ‘perfect’ protein because all of the nitrogen from that food is retained by the body.

The nutritional value of proteins from animal sources is determined by the source (animal) and the part of the animal. For example, beef liver has a PBV of 80 while chicken breast has a PBV of 88.5.

This means that more of the nitrogen from chicken breast is retained in the body than from beef liver.

When looking at the PBV of a protein, it is important to consider the whole animal. For example, chicken meat has a PBV of 80 while chicken feet have a PBV of only 20.

This means that chicken feet are not a good source of protein for your pet.

So, how do you know if a protein source is high quality?

A good rule of thumb is to look for a protein source with a PBV of 70 or above.

Here is a list of some common pet food ingredients and their PBVs:

  • Beef: 74
  • Chicken: 80
  • Egg: 100
  • Fish: 94
  • Lamb: 74
  • Turkey: 78

While the PBV is a good way to compare the quality of protein sources, it is important to remember that not all proteins are created equal.

For example, a chicken breast has a higher PBV than a chicken thigh but that does not mean that the chicken breast is a better source of protein.

In fact, the chicken thigh contains more protein and amino acids than the chicken breast.

Now that you know all about the PBV of proteins, you can be sure to choose the best sources of protein for your pet!

Factors that Determine PBV

The two main factors that determine PBV are digestibility and the amino acid composition of the protein.

Animal Body part:

As we mentioned earlier, some animal body parts are not as digestible as others and therefore, have a lower PBV.

For example, feathers have a very low PBV because they are not very digestible.

Amino Acid Composition:

The amino acid composition of the protein also plays a role in determining the PBV.

Amino acids are the building blocks of proteins and some amino acids are more important than others for growth and repair.

For example, the amino acid cysteine is important for the formation of keratin, which is a key component of hair and nails.

Therefore, a protein that contains a lot of cysteine will have a higher PBV than a protein that does not contain much cysteine.

Biological value: Measuring the protein’s worth

The biological value (BV) is a measure of the nitrogen retention in the body from a foodstuff as measured by the protein’s ability to supply amino acids — especially the 10 essential amino acids.

BV divides the protein used by the protein available as per the formula below;

  • BV = (protein used/protein available) x 100

Eggs: The Gold Standard of BV for Proteins:

Eggs have a score of 100% on the BV scale, making them the perfect protein. This is because they contain all 10 of the essential amino acids in adequate ratios for pets.

Every other protein food has a lower score than eggs, including beef (78), chicken (80), fish meal(92).

Below is a list I got from Dogs Naturally Magazine with BVs of different protein sources

  • Eggs … 100
  • Milk … 93 (but don’t forget, a lot of dogs are lactose intolerant)
  • Fish meal – 92%
  • Chicken … 79
  • Fish … 76 
  • Beef … 75
  • Wheat gluten … 64
  • Tofu … 64
  • Rice … 59
  • Oatmeal … 55
  • Bread … 54
  • Lentils … 50
  • Wheat gluten … 41

Below is a table from Dog Food Advisor where they quote Liz Palika who wrote the book, ‘The Ultimate Pet Food Guide”


Ideal sources of various amino acids that dogs get from Protein Sources:

  • Arginine – fish, meat, mushrooms, spirulina, sprouted beans and legumes
  • Histidine – meat, fish, nuts, seeds, eggs
  • Isoleucine – eggs, spirulina, poultry, game, fish, pork
  • Leucine – meat, spirulina
  • Lysine – meat, fish, shellfish, eggs
  • Methionine – meat, eggs, dairy (remember, many dogs are lactose intolerant)
  • Phenylalanine – meat, fish, eggs, milk
  • Threonine – meat, eggs, liver, fish, seeds, nuts
  • Tryptophan – meat, dairy
  • Valine – meat, fish, seeds, nuts, mushrooms 

Ruminant and poultry recipes need separate strategies to balance the fats.

Ruminant recipe such as beef and lamb have more saturated fats ( the “bad” fats). Poultry recipes have more polyunsaturated fats (the “good” fats).Saturated fats can have an impact on cholesterol levels.

Polyunsaturated fats like those found in poultry help to reduce cholesterol. The best strategy is to use a variety of protein sources in your recipes to get the benefits of both kinds of fat.

Benefits of saturated fat:

  • -Saturated fat provides energy for working muscles
  • -Saturated fat helps the body absorb essential vitamins
  • -Saturated fat supports the immune system
  • -Saturated fat is necessary for the production of hormones

Benefits of polyunsaturated fat:

  • -Polyunsaturated fat lowers cholesterol levels
  • -Polyunsaturated fat reduces the risk of heart disease
  • -Polyunsaturated fat helps to reduce inflammation

Oils such as canola, sunflower, and flaxseed oil are good sources of essential fatty acids. Adding these to your pet’s diet will help balance the ratio of omega-6 to omega-3 fatty acids.