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Protein is composed of amino acids, which are the building blocks of the body. While most people often mistakenly are concerned about the protein content of food, in reality it is the amino acids that are important. The protein sources used in formulating the diet must contain the proper amounts of the essential amino acids needed, or your fur kids will suffer from an amino acid deficiency despite an adequate protein intake.
We do not eat protein for the sake of protein. Dietary protein intake is all about acquiring the necessary amino acids our bodies, and those of our pets, need or require. Think of protein as the suitcase, and amino acids, as the building blocks contained in the suitcase.
Protein from animal sources, such as meat and milk, is called complete, because it contains all nine of the essential amino acids. Most vegetable protein is considered incomplete because it lacks one or more of the essential amino acids.
Dietary protein can come in many forms from many sources. The most natural and digestible (bio-availability) form for dogs and cats comes in meat and fish. Dogs have evolved to consume relatively high quantities of meat, and their physiology has adapted to easily digest and utilize the nutrients the meat contains. This is why nutritionists always put so much emphasis on the meat content of a food.
Unfortunately, meat can be an expensive ingredient, and many lower grade McKibble and McCan cut costs by substituting meat with cheaper protein sources: e.g. soya meal, maize gluten, potato protein, vegetable protein and so on. Proteins from non-meat sources are harder for your fur kids’ body to digest and have a higher chance of causing dietary intolerance.
While plants can produce all of the 24 amino acids, they can’t really produce enough of each or in the right amounts. With few exceptions, an all-plant (vegetarian) diets would not provide enough of the right amounts and right balance of amino acids required for our pets. Keep in mind that cats are true carnivores, requiring meat in their diets; and even though dogs are more omnivorous than cats, they too are carnivores and must have meat in their diets.
Traditionally, most adult grain-based dry foods or kibble contained 20-30% protein (about 5-8% in wet foods) (based on as fed profiles, not as Dry Matter) and many dog owners and dog food manufacturers have suggested that higher protein diets can be harmful in the past. However, more recently, a new wave of high-meat / high-protein foods (and research) have shown that as long as it comes from good animal sources, dogs and cats are more than capable of handling high amounts of protein. For per parents feeding on BARF or PMR, protein ratios below 40% seems irrational. Newly published research have proved that high protein intake does not cause orthopedic problems in puppies, nor kidney disease in older dogs, as was the believe and thought process in the past.
Good Specie-Appropriate Protein is highly beneficial; it supports the immune system and the central nervous system, contributes to healthy skin and coat and to wound healing, and helps to maintain lean body mass while lowering the percentage of body fat. Dogs fed a high-protein diet are often calmer and less hyper than dogs fed on high-carb diets. Higher protein is one of the major benefits of feeding raw or home made diet to dogs, though you can also increase the protein level by adding fresh, high-protein foods to a commercial diet. As with most things, when it comes to protein, quality is much more important than quantity.
Protein supplied in most McKibble and McCan through animal or plant materials, are typically made from “animal meal” or “animal by-products” that than the whole, dressed animal. These less wholesome ingredients are not desired in the diets of pets.
- Tissue building and growth, the structural components of cells;
- Movement by muscle contraction;
- Providing strength with flexibility in ligaments, tendons and cartilage;
- Transport (haemoglobin) and storage of oxygen in muscles (myoglobin);
- Transport of other nutrients, e.g. lipids as lipoproteins.
Protein serves as:
- Enzymes – catalysts in many metabolic reactions. All enzymes are proteins.
- Hormones – controlling metabolism, growth and reproduction. Not all hormones are proteins.
- Body protection
- Lubricants in mucus help prevent physical damage;
- Innate immunity, skin, nails, claws, etc.;
- Adaptive immunity, antibodies.
- Energy source.
Protein deficiency can interfere with any of the above systems, leading to poor growth or loss of body weight, poor coat condition and impaired immunity among other problems.
The biological value of protein is based on the protein’s unique combination of its building blocks, the amino acids. People and animals use the amino acids obtained by digestion of protein for growth and building tissues and organs.
When discussing proteins, the biological value of the protein is important. Eggs are ranked at 100, being considered the best food for providing high-quality protein. Digestibility is also important; the protein must be easily digested and assimilated into the body before it can be of any value to your fur kids.
While it would be most helpful to know the amino acid content of the protein in the commercial pet foods, the label only needs to list the crude protein legally. It’s important to read the label to see the quality of ingredients, as crude protein can include items such as feather meal, hair, hooves, tendons, and ligaments. While these animal by-products certainly provide protein, they are essentially non-digestible and provide no biologic value (amino acids) to your fur kids.
|Citrulline (conditional in cats)||Asparagine|
|Taurine (essential in cats)||Serine|
In addition to supplying the ten essential amino acids, dietary protein is also the body’s primary source of nitrogen. The body needs nitrogen to synthesize the non-essential amino acids and other molecules necessary for life, such as various hormones and neurotransmitters. The body can only synthesize protein if all essential amino acids are present in a sufficient amount. If even one essential amino acid is deficient, the entire process of protein synthesis shuts down, regardless of how much of every other amino acid is available.
If more protein is consumed than needed for growth, repair and other functions, the excess is used for energy or stored as fat. This leaves nitrogenous waste, which is converted to urea by the liver and excreted primarily through the kidney. In the past, it was believed that energy is produced less efficiently from protein than from fat or carbohydrate for dogs. However, with recent studies, these views are changing.
The body’s dietary requirement isn’t for protein per se; it is for essential amino acids. As the building blocks of protein, amino acids are the building blocks of life. So, for a protein source to be high quality, it must supply the correct composition of essential amino acids. It must also have a high biological value, meaning that the body can efficiently absorb and utilize the amino acids and nitrogen the protein supplies. Based on these criteria, the highest quality proteins for dogs come from animal sources. The winners (in alphabetical order) are: Dairy; Eggs; Fish; Muscle meats; Organ meats.
Biological Value of Proteins
The biological value of protein describes how efficiently a protein is used by your fur kids. This value is high for proteins from meat, most meat by-products, eggs and dairy products, as discussed above. Dog and cats digest these proteins efficiently and they provide amino acids in proportions suitable for tissue protein synthesis. In contrast, the biological value of most plant proteins is low, due to insufficiency of specific amino acids and lower digestibility of these proteins. Careful balancing of proteins from plant sources can improve a diet’s protein quality and could make them suitable for meeting pets’ needs, however, the biological values of commercial grain-based pet food proteins are largely unknown. Their value or availability changes when combined with other ingredients, and after processing during the production process. A nutrient’s adequacy and availability can be known only through feeding trials, something most commercial pet food manufacturers try to avoid.
“High quality” takes on new meaning when it is re-defined to include sources that are functional. Here’s how we define a high quality, functional protein according to the principles of nutrigenomics, as published by Dr Jean Dodds and Diana Laverdure in their book titled Canine Nutrigenomics :
- Bioavailable (easily digested and assimilated);
- Free of contaminants such as chemicals, hormones and antibiotics;
- Does not promote a food intolerance/sensitivity;
- Does not contain compounds that send unhealthy messages to the epigenome, triggering unhealthy gene expression;
- Unadulterated (e.g., non-GMO) and unprocessed or minimally processed.
Based on this definition, we encourage you to rotate among the following functional, high quality protein sources:
- Eggs (preferably free-range and organic);
- Fish that are low in mercury, including sardines, wild-caught Alaskan salmon (avoid farm-raised), Pollack and catfish. Avoid high-mercury fish such as tuna (especially albacore or white tuna), King mackerel, tilefish, shark and swordfish. We also typically do not recommend giving your dog shellfish, such as shrimp, crab, lobster, oyster and clams, since some dogs can experience the same severe allergic reactions as people;
- Muscle meat and organ meat from novel animal sources, such as game (venison), duck, goat, pork, rabbit and turkey (preferably grass fed and naturally raised without hormones or antibiotics). These sources are less likely to cause food intolerance / sensitivities than more common animal proteins, such as beef, chicken and lamb.
The amount of protein your dog requires depends upon his age, activity level, specific health issues and also the quality of the protein. Remember that the less bio-available the protein source, the more of it your dog will need in order to assimilate the amino acids. So, if your fur kid eats a commercial diet chock full of inferior quality, grain-based proteins, that diet will need to contain a higher percentage of protein than a home-prepared diet relying on fresh, highly bio-available animal protein sources.
Meat Proteins Taken To Extreme Temperatures?
When the meats used in commercial pet foods are initially processed, they are dried by exposure to significant heat. When the cans containing the final product are sterilized, they are exposed to further heat. When dry pet foods are extruded into pellets, they are exposed to temperatures of up to 170C (some sources say temperatures reach 204C) to bond the ingredients together. Heating meat to high temperatures causes the generation of two groups of chemicals known to stimulate cancer, HCAs (heterocyclic amines) and PAHs (polycyclic aromatic hydrocarbons). HCAs are thought to begin to form in meat at about 150C. The longer the meat remain at high temperature, the more it is formed. We know these compounds are suspects in the cause of colon cancer in humans. In one study 1, chronic intestinal inflammation preceding that made people 6 times more likely to develop it. How and if this relates to intestinal disease in cats and dogs we cannot say because no one has examined the issue. Others feel that there are more important concerns regarding the oxidation in processed foods.
Wholesomeness & Digestibility
As we stated above, the digestibility and biological value of any commercial pet food depends mostly on its raw ingredients. Most first world governments, and industry, also call for pet food ingredients to be “wholesome”. The definition of wholesome is “good for one’s health” or “healthful”. Wholesomeness has an important effect on digestibility and biological value of nutrients. Pet parents and guardians whom prepare their own food can easily select the most wholesome ingredients to make up their fur kids’ diets. Pet parents and guardians feeding commercial pet foods have little control over wholesomeness of the product. Because plant proteins are not complete for providing essential amino acid needs, some animal proteins or amino acids must be included in the formula fed. In general, as you will know by now, animal proteins are more expensive than plant protein sources. The cost of commercial grain-based pet foods is kept as low possible by using no more animal protein than is necessary. Ingredients listed (and defined by AAFCO) on a pet food label that are not likely to be wholesome include:
- Meat meal is rendered product from animal tissues exclusive of any added hair, hoof, horn, hide trimmings, manure, stomach and rumen contents, except in such amounts as may occur unavoidably in good processing practices.
- Meat and bone meal is the rendered product from mammal tissues including bone, exclusive of any added hair, hoof, horn, hide trimmings, manure, stomach and rumen contents, except in such amounts as may occur unavoidably in good processing practices. It shall not contain added extraneous materials not provided for in this definition.
- Animal by-product meal is rendered product from animal tissues exclusive of any added hair, hoof, horn, hide trimmings, manure, stomach and rumen contents, except in such amounts as may occur unavoidably in good processing practices.
- Meat by-products derived from slaughtered mammals is non-rendered, clean parts, other than meat. It includes lungs, spleen, kidneys, brain, livers, blood, bone, partially defatted fatty tissue, and stomach and intestines freed of their contents. It shall be suitable for use in animal food.
- Poultry by-products must consist of non-rendered clean parts of carcasses of slaughtered poultry such as heads, feet, viscera, free from fecal content and foreign matter except in trace amounts as might occur unavoidably in good factory practice.
- Meat is the clean flesh derived from slaughtered mammals and is limited to that part of the striated muscle which is skeletal or that which is found in the tongue, in the diaphragm, in the heart, or in the esophagus with or without accompanying fat, skin, sinew, nerve, and blood vessels.
- Poultry by-product meal consists of the ground, rendered, clean parts of the carcass of slaughtered poultry, such as necks, feet, undeveloped eggs, and intestines, exclusive of feathers, except in such amounts as might occur unavoidably in good processing practices.
Slaughtered animals can also provide protein for animal feed when a diseased carcass is condemned for human use. In other cases, protein contaminated with fecal material is condemned for human consumption, but not for animal food ingredients. Some protein in commercial pet foods is from animal parts that humans do not consume for esthetic reasons. Some meat sources of protein have nutritional limitations in diets for pets.
Analyses of protein ingredients, such as meat and bone meal, show great variability based on raw produce used in the production processes of commercial kibble. There are virtually no standards for this anywhere in the world, so that some products may contain greater amounts of bone than is needed. There is also no analysis on amino acids that meat and bone meal provides when mixed with other foodstuffs as part of the feeding formula. Most non-meat proteins in commercial pet foods cannot, by themselves, provide a completely balanced diet. For example, vegetable proteins are deficient in the amino acid lysine. As a result, commercial pet foods need meat products to provide enough lysine. Meat and bone meal is a source of lysine, but heat used during rendering to make meat meal, typically destroys lysine. Therefore, commercial pet food must be analysed to determine if it contains adequate amounts of lysine. Unfortunately, most commercial pet food manufacturers do not publish these details for public consumption.
Unique Feline Needs
Cats have a number of unique nutritional needs and their diets must be formulated differently from canine diets. Feline diets must provide proteins containing essential amino acids for which cats have an absolute requirement. Dietary proteins must also provide more nitrogen than for most other animals. This is due to cats not being able to conserve nitrogen as well as other animals. Their enzyme activities for metabolizing amino acids are greater than in other animals and that activity does not decrease when they eat a low protein diet. Excess amino acid destruction continues, leaving insufficient amounts for making protein. Many animals can survive on protein intakes of 4% to 8% of the total dietary calories. In contrast, cats need 18% to 20% of total calories as protein for growth and 12% to 13% for adult maintenance.
As a result, cats need two to three times more protein than most other animals under comparable circumstances. The 18% to 20% of total calories for a growing kitten represents about 25% of the dry weight of the diet. Most commercial cat foods contain 30% to 35% protein on a dry basis, which is an excess because cats poorly digest the proteins in these diets. Commercial kibble-based diets formulated for dogs contain too little protein for feeding cats. Cats cannot synthesize the essential amino acid citrulline (see: Unique nutrient requirements of cats appear to be diet–induced evolutionary adaptations, J.G. Morris (PDF)) 2, that is low in any food. However, cats can convert arginine to citrulline, and that means that feline diets must contain arginine to meet the need for citrulline. Cats fed a diet lacking arginine develop hyper-ammonemia and show clinical signs of illness within several hours of feeding. Ammonia accumulates because it it is not converted to urea; arginine and citrulline are needed for that conversion.
Feline diets must contain arginine. Cats have only a limited ability to synthesize the essential amino acid taurine from sulfur-containing amino acids. Therefore, a cat’s diet must provide sufficient taurine.3 It also helps for the diet to be rich in sulfur-containing amino acids. Diets low in protein, and therefore sulfur-amino acids, are more likely to induce taurine deficiency. Taurine is the most abundant free amino acid in the body. It is not incorporated into body proteins. Its many important functions include being a precursor for bile salts. Both cats and dogs have an obligatory and continuous requirement for taurine to make bile salts to replace bile salts lost continuously in the feces. Taurine is also involved in growth and maturation of nervous tissue, maintenance of normal vision, normal heart function, and female reproduction. Taurine is found in all animal tissues, but not in plant materials. Since taurine is free, not incorporated in proteins, in animal tissues, it readily leaches out in water. Cooking meat in water and discarding the water can greatly reduce its taurine content. Feeding proteins from plants such as soybeans and from animal products such as cottage cheese provide no taurine. Canned diets require higher concentrations of taurine to maintain normal levels than dry foods, for example.
No reason is known for this difference other than the two dietary requirements have disparate formulations. Within the last decade, two diseases, dilated cardiomyopathy (DCM) 4 and central retinal degeneration, appeared in cats fed commercial diets containing insufficient taurine. Only some animals’ problems can be reversed with taurine supplementation, so it is important that taurine is adequate in any feline diet. Taurine deficiency does not appear in cats living under natural conditions, catching their own food, or where the animal is eating what nature designs a carnivore to eat, meat, or as we like to express, biologically species appropriate raw meals. Dry expanded cat foods have a safe taurine concentration if it exceeds 1200 milligrams taurine per kilogram dry matter. In contrast, canned foods need at least 2000 milligrams taurine per kilogram dry matter to maintain adequate plasma concentrations.
Cats show low tolerance for the amino acid glutamic acid. Excess amounts cause sporadic vomiting and thiamin deficiency. Glutamic acid is abundant in vegetable proteins and is comparatively low in animal proteins.
Cats also have some unique vitamin needs. Cats do not have the ability to convert carotene to vitamin A. Lacking the enzyme for that conversion makes it necessary for cats to have vitamin A in their diet. Cats also do not have the capacity for converting tryptophan to the niacin. Cats metabolize tryptophan too rapidly to other compounds. As a result, the species appropriate diet must provide niacin (Vitamin B3). Cats and dogs cannot manufacture vitamin D or its precursor 7-dehydrocholesterol. As a result, the species appropriate diet must also provide vitamin D.
Additional Articles and Videos
Good reference articles and further reading available at:
- How much meat is really in that bag of pet food? Requires Adobe (Natural Pet Products);
- Dog Nutrient Requirement, The Waltham Book of Companion Animal Nutrition, (Waltham) ;
- Cat Nutrient Requirement, The Waltham Book of Companion Animal Nutrition, (Waltham);
- Two Proteins to Avoid for Your Pet, (Mercola) .
References and Research
- 1.Mizushima T, Ohno Y, Nakajima K, et al. Malignancy in Crohn’s Disease: Incidence and Clinical Characteristics in Japan. Digestion. 2010:265-270. doi:10.1159/000273784