Canine Protein Needs

There are three main energy units for dogs: fat, carbohydrates and protein. These are what we refer to as our pet’s macronutrients. Depending on your dog’s individual nutritional needs based on things like age, activity level, and medical conditions - protein needs will vary. However research has shown us that dog’s require certain amino acids - also called “essential amino acids” within their diet in order to sustain life.

These minimal essential amino acids are described in both the NRC, AAFCO and FEDIAF by life stage.

The Purpose of Protein in Dog Food

1. Formation of muscles and tissues of the body.

2. Replacement of tissues and cells proteins

3. Help in the formation of enzymes and hormones of the body.

4. Immune function

5. Maintain body fluid balance

6. Supply glucose to the body

7. Regulate acid-base balance

8. Essential for the formation of egg, milk protein, wool and hairs of the animal

Protein Requirements in Dogs

Depending on your dog’s age and activity level their requirements may vary. And though we do have minimum established protein requirements by the NRC (National Research Council), AAFCO (Association of America Feed Control Officials) and FEDIAF ( European Pet Food Industry Federation), we do not have established “ideal” amounts of protein, nor is there an established upper limit of protein.

The main reason for this is that protein needs change over time - sometimes as often as daily due to changes in activity. They will also change during certain disease processes. Protein needs are not one-size fits all. 

This is also why you may find some foods on the market for specific diseases and conditions (like kidney disease) where protein is below AAFCO/FEDIAF recommended minimums. However even these foods will be above the NRC recommended values.

OrganizationRequirement of ProteinNational Research Council (NRC)25g / 1000 kcalAAFCO Adult Maintenance45g / 1000 kcalAAFCO Growth & Reproduction (Puppy)56.3g / 1000 kcalFEDIAF Adult Maintenance45-52.1g / 1000 kcalFEDIAF Growth50-62.5g / 1000 kcalMost Dogs (Low to Moderate Activity)60-90g / 1000 kcalHighly Active (6-8+ hours Activity)75-90g+ / 1000 kcalWeight Loss (caloric restriction)75g+ / 1000 kcalHealthy Senior Dog (high cellular turnover)75g+ / 1000 kcal

Protein in Dog Food:

If you are looking at or comparing protein within dog food it's important to realize that protein on the guaranteed analysis is on an "as fed basis". This means that these values are influenced by the moisture content and the caloric density of the diet.

This in turn means if you are looking to compare protein content between two pet foods you need to convert the guaranteed analysis crude protein to a caloric basis or grams per 1000 kcals.

CALCULATION:

(% Crude Protein + 1.5)/( kcal/kg / 10,000) = grams of protein per 1000 kcal

Example:

A great example of this is if we compare the Hill's Perfect Digestion which is 25% crude protein, with the Purina Pro Plan Sensitive Skin and Stomach which is 26% crude protein. Because the moisture content in the Purina Pro Plan as listed is higher, in combination with a higher caloric density (>4000 kcal/kg) - this actually makes the protein per calorie fed (g / 1000 kcal) LESS.

But when we think of our dog’s protein needs amount isn’t everything.

The profile of the individual amino acids matters - aka: is it a “complete” protein? The bioavailability and digestibility of the protein matters - aka: can my dog utilize this protein effectively?

Essential Amino Acids:

Dogs have TEN essential amino acids. These amino acids are required for various metabolic functions such as muscle growth, tissue repair, enzymes, immune fictions, and enzymes. The fact that they are essential means that they cannot be manufactured and must come from the diet.

These essential amino acids are:

ArginineIs needed for ornithine synthesis. Ornithine coverts released nitrogen (from protein metabolism) into urea. This can lead to hyper-ammonia in the case of deficiency.HistidineInvolved with the regulation of histamine, anerine and carnosine. Also plays a role in oxygen exchange and deficiency can lead to changes to serum albumin and hemoglobin.IsoleucineBranched-Chain Amino acids are particularly important for cognitive health & skeletal muscle repair.LeucineBranched-Chain Amino acids are particularly important for cognitive health & skeletal muscle repair. Strongly Ketogenic. Indirectly helpful for suppressing skeletal muscle degradation. Tends to be an limiting amino acid.LysineOften deficient in low-protein diets, cereal-based diets. Will form Millard reactions with Glucose under HEAT that makes it unable to be utilized. Excessive Lysine can cause amino aciduriaMethioninePrecursor to Taurine Synthesis, Considered the most limiting amino acid because most proteins are low in methioninePhenylalaninePrecursor to Tyrosin, 2x NRC Rec requirements is needed for black-coated animals due to Tyrosin's involvement in melanin productionThreonineA gluconeogenic amino acid, precursor to glycine. If supplemented needs to be in the L-Threonine form to be utilized.TryptophanPrecursor for niacin formation. Involved in neurotransmitters serotonin & melatonin - may have so neurobehavioral benefits such as reduced aggression in dogs.ValineBranched-Chain Amino acids are particularly important for cognitive health & skeletal muscle repair.

Other Amino Acids of Note in particular situations:

• Alanine and Glutamine are important for dogs using gluconeogenesis to create glucose as an energy source from amino acids. If these amino acids are too low in a low carb diet, it can lead to protein deficiencies.

• Taurine is synthesized from methionine and cysteine. However since methionine is often a limiting amino acid - decreased digestibility, Millard reactions, and fiber content can affect bioavailability. Potentially lead to deficiencies.

Evaluating Protein Quality:

When we consider the "quality" of the protein - we have to not just look at the amount of protein. We also need to consider the essential amino acid composition, digestibility, and bioavailability of those amino acids.

Assessing a Protein's Amino Acid Composition:

Chemical Score: Compares the amino acid profiles of a given protein with the amino acid profile of a reference for very high quality (usually egg protein). This is used to asses the most limiting amino acids within a protein source.

The Chemical Score Evaluates Essential Amino Acid Composition

Chemical ScoreFood1eggs0.95chicken0.92beef0.91soy0.78chickpeas and edamame0.73vegetables0.7other legumes in general0.687house cricket0.59cereals and derivatives0.597cooked peas0.5rices0.25wheat gluten

Assessing Protein Digestibility:

Protein Digestibility is the percent of ingested protein that is not excreted in the feces. Basically digestibility looks at what goes in vs. what comes out.

Typically when we consider different types and preparations of protein sources we find, generally speaking that...

• Animal-based proteins are typically more digestible than plant-based proteins.

• Fresh Proteins - such as minced meat and cuts of meat are higher in digestibility (>90%)

• Prolonged heat processing decreases animal protein digestibility, but can increase digestibility of plant-proteins

• Protein Digestibility does vary based on breed (though we have limited research in this area)

• Protein Digestibility decreases with age

• Soluble Fiber Content (not insoluble) can decrease protein digestibility

• Diseases / Conditions can affect protein digestibility as well such as IBD, Pancreatitis, Hepatic Disease, Kidney Disease etc.

That being said - there are exceptions in that soy meal when properly processed at similar digestibility to meat meals. And individual protein digestibility can vary.

Assessing Protein Bioavailability:

Protein Bioavailability is the degree to which the ingested protein in a particular source is absorbed and is able to be used in an animal's metabolism.

When we look at digestibility numbers at different points along the digestive tract. Absorption of protein and amino acids takes place in the small intestine. However proteins not absorbed, or not able to be broken down will pass into the large intestine. Here microbes will sometimes break down additional proteins into by-products that are utilized by the microbiome.

What this means practically is if we took a digestibility value at the ileum of the small intestine, it may be 1-20% lower than that of a digestibility in the stools. And that 1-20% is not being utilized by the animal, but by bacteria in the large intestine- aka not "bioavailable" to the animal.

Protein Digestion:

In dogs (and cats!) when they ingest a food item that contains protein - a kibble, or say chicken breast- digestion starts within the stomach.

When protein containing foods enter the stomach, hydrochloric acid and pepsinogen are released. Hydrochloric acid works to denature proteins, this unfolds the protein molecule and exposes the peptide bonds. While this is going on pepsinogen is produced and interacts with hydrochloric acid which converts it to pepsin. Pepsin will then work to digest about 10-20% of protein molecules within the stomach.

In order for this entire process to occur the stomach must be kept to a pH between 2-3 (acidic), as anything more basic will cause pepsin to not work as effectively.

From there protein and peptide molecules will travel to the small intestine where they mix with pancreatic enzymes - trypsin, chymotrypsin and carboxypeptidase. These pancreatitis enzymes will break down large polypeptide chains into smaller polypeptides and some free amino acids.

These then pass to the small intestinal “brush border”, which is the inner lining of the small intestine. This boarder contains further protein digesting enzymes such as dipeptidase and tripeptidase - which break down these smaller polypeptides into free amino acids which can be absorbed into blood circulation.

Protein Deficiency in Dogs:

In dogs protein deficiency results from either low protein within the diet, poor digestibility/bioavailability of the protein in the diet, a diet moderate in protein that is also low in carbohydrates or the missing of essential amino acids. Cases of protein deficiency is fairly rare in dogs fed commercially available products, however it can happen with poorly formulated products, or underfeeding.

This can lead to:

• Losses in Lean Body Mass

• Weight Loss

• Impaired Reproduction

• Impaired Growth

• Impaired Immune Function

• Impaired Performance

• and in some cases - organ failure or death

What happens when you feed too much protein?

Any proteins not digested and absorbed in the small intestine is taken to the large intestine to be digested by microbial digestion/fermentation which produces odiferous compounds such as indoles, cresol. Any unused ammonia by bacteria is absorbed into the blood and then to the liver where it is converted to urea and excreted in the urine.

This is why you often see increases to urine protein or blood urea nitrogen when animals are fed diets higher in protein than they need.

Protein is converted to glucose?

Yes, believe it or not - if your dog doesn’t get enough glucose (starch aka carbohydrates) within their diet they will utilize the amino acids you are providing as a source of glucose.

This happens by the liver breaking down the amino acids - the amino group is removed and excreted via urea in the urine (via the urea cycle which costs 5 ATP per ammonia (amino acid) molecule to excrete), while the carboxyl group is converted to glucose.

This process can cause protein deficiency in dogs. In a low carbohydrate diet, protein will need to be converted into glucose to fuel the brain and other glucose-dependent organs. If the diet in question is also borderline low in protein, the process will still occur as brain function is placed as a priority. This can cause muscle wasting, poor skin/coat, and more if fed long-term.

Protein Dog Food Basics - Take Aways:

• If comparing dog food make sure to convert the % Crude Protein to g/1000kcal

• Having a complete Essential Amino Acid Profile is just as important as the Amount of Protein in the Diet.

• Protein Digestibility and Bioavailability make a big difference to how much protein your dog will utilize.

• Protein Deficiency is rare unless the diet is unbalanced, poorly digestible, or your dog is underfed.

• Excess Protein is not stored, it is broken down as an energy source