Canine Protein Requirements Part 2b Definitions

In Part 2a of this series I talked about the fact that protein is made up of amino acids which are chemical units or building blocks. Today I am going to take a closer look at these acids and how they relate to our dogs’ diet.
Arginine is an alpha amino acid. It is one of the 20 most common natural amino acids. Generally, in mammals it is classified as a semi-essential or conditionally essential amino acid, depending on the developmental stage and health status of the animal. Puppies are unable to meet their requirements and thus arginine is nutritionally essential for these youngsters. The AAFCO Nutrient Profile for Dog Food classifies arginine as an essential amino acid and its presence in dog food is required at a minimum of 0.51% for adult maintenance and 0.62% for growth and reproduction profiles. Arginine plays an important role in cell division, the healing of wounds, removing ammonia from the body, immune function, and the release of hormones. The benefits and functions attributed to arginine include among others: Stimulation of the release of growth hormones, improves immune function, reduces healing time of bone injuries, increases muscle mass, reduces tissue body fat an helps decrease blood pressure. Arginine is found in a wide variety of foods. They include animal sources like dairy products (cottage cheese, milk, yogurt, whey protein), beef, pork (bacon and ham), poultry (chicken and turkey light meat), wild game (pheasant, quail), seafood (salmon, tuna in water) and vegan sources like wheat germ, oatmeal, nuts (coconut, pecans, cashews, walnuts, almonds, Brazil nuts, hazel nuts, pine nuts, peanuts), seeds (pumpkin, sesame, sunflower), cooked soy beans. Research has also shown that a low carbohydrate, high protein, high arginine (meat amino acid), low omega-6 fatty acid and high omega-3 fatty acid diet is useful for both preventing and treating cancer.
Histidine is one of the 20 standard amino acids present in proteins. For dogs, since they don’t produce this amino acid in sufficient volume on their own, it is considered to be essential. AAFCO standards require its presence in dog food at a minimum of 0.18% for adult maintenance and 0.22% for growth and reproduction profiles.
Isoleucine is an essential alpha amino acid. As an essential amino acid, isoleucine is not synthesized in animals, hence it must be ingested, usually as a component of proteins. AAFCO requirements for its presence in dog food is a minimum of 0.37% for adult maintenance and 0.45% for growth and reproduction profiles.
Leucine is an essential alpha amino acid, which means that dogs cannot synthesize it. Hence it must be ingested, usually as a component of proteins. AAFCO required minimums are 0.59% for adult maintenance and 0.72% for Growth and reproduction stage. As a dietary supplement, leucine has been found to slow the degradation of muscle tissue by increasing the synthesis of muscle proteins Leucine is utilized in the liver, adipose tissue, and muscle tissue.
Lysine is an essential amino acid. Lysine is a base like arginine and histidine. It must be provided with the food. Lysine is important for proper growth and it plays an essential role in the production of carnitine, a nutrient responsible for converting fatty acids into energy and helping to lower cholesterol. Lysine appears to help the body absorb and conserve calcium and it plays an important role in the formation of collagen, a substance important for bones and connective tissues including skin, tendon, and cartilage. If there is too little lysine in the diet, kidney stones and other health related problems may develop including loss of appetite, slow growth, and reproductive disorders. It is extremely rare, however, to obtain insufficient amounts of lysine through the diet. Generally, only vegetarians are at risk for deficiencies. For them, legumes like peas are the best alternative source. Regular good sources of lysine are foods rich in protein including meat like red meat, pork, and poultry, fish like cod and sardines, nuts, eggs, soybeans, spirulina, and fenugreek seed.
Studies conducted to identify the requirement of lysine for dogs show that a young female dog was found to require between 0.461% and 0.577% dietary lysine for dogs for optimum growth and nitrogen balance. For young male dogs they would need lysine starting from a range of 0.577% for a maximum growth and nitrogen balance. AAFCO standards require 0.77% for growth and reproduction stages, 0.63% for adult maintenance.
Methionine (-Cystine) is an essential alpha amino acid. Together with cysteine, methionine is one of two sulfur-containing proteinogenic amino acids. High levels of methionine can be found in sesame seeds, Brazil nuts, fish, meats, and some other plant seeds. Most fruits and vegetables contain very little of it; however, some have significant amounts, such as spinach, potatoes, and boiled corn. Most legumes, though high in protein, are also low in methionine. DL-methionine is sometimes added as an ingredient to pet foods Methionine, cysteine, and soy protein heated in a small amount of water creates a meat-like aroma. AAFOC requirements call for a 0.53% methionine cystine content in food for growth and reproduction stages and minimum 0.43% for adult maintenance. Methionine is a principle supplier of sulfur which prevents disorders of the hair (promotes hair growth), skin and nails. It helps lower cholesterol levels by increasing the liver's production of lecithin, reduces liver fat, and protects the kidneys. dl-methionine is a chelating agent for heavy metals. It regulates the formation of ammonia and creates ammonia-free urine which reduces bladder irritation. dl-methionine is an essential amino acid which serves as a urinary acidifier. Methionine typically is added as supplement to cat food to create acidic urine. In dog foods, the meat normally supplies sufficient amounts.
Cystine is the amino acid dimer formed when a pair of cysteine molecules are joined by a disulfide bond (refers to the structural unit composed of a linked pair of sulfur atoms). In animal food disulfide bonds can be broken at temperatures above about 150 °C, especially at low moisture levels below about 20%. One of the richest nutritional sources of cystine in the diet is undenatured whey proteins from milk. The disulfide bonded cystine is not digested or significantly hydrolized by the stomach, but is transported by the blood stream to the tissues of the body. Here, within the cells of the body, the weak disulfide bond is cleaved to give cysteine, from which glutathione can be synthesized.
Cysteine is an alpha amino acid and is a non essential amino acid, which means that dogs can synthesize it. Because of the high reactivity of this thiol, cysteine is an important structural and functional component of many proteins and enzymes.
Phenylalanine Tyrosine Phenylalanine is an alpha amino acid found naturally in the breast milk of mammals and manufactured for food products. L-Phenylalanine (LPA) is an electrically-neutral amino acid, one of the twenty common amino acids used to biochemically form proteins.. Breast milk from mammals is rich in phenylalanine. It is also produced by plants and most microorganisms from prephenate, AAFCO requirements call for a 0.89% phenylalaline tyrosine content in food for growth and reproduction stages and minimum 0.73% for adult maintenance.
Tyrosine is one of the 20 amino acids that are used by cells to synthesize proteins. This is a non-essential amino acid and it is found in casein. In fact, the word "tyrosine" is from the Greek tyros, meaning cheese, as it was first discovered in 1846 by German chemist Justus von Liebig in the protein casein from cheese. Casein is the predominant phosphoprotein that accounts for nearly 80% of proteins in milk and cheese. Mammals synthesize tyrosine from the essential amino acid phenylalanine, which is derived from food.
Threonine is an alpha amino acid. AAFCO requirements call for a 0.58% threonine content in food for growth and reproduction stages and minimum 0.48% for adult maintenance. As an essential amino acid, threonine is not synthesized in dogs, hence they must ingest threonine in the form of threonine containing proteins. Foods high in threonine include cottage cheese, poultry, fish, meat, lentils, and sesame seeds.
Tryptophan is one of the 20 standard amino acids, as well as an essential amino acid in a dog’s diet. AAFCO requirements call for a 0.20% tryptophan content in food for growth and reproduction stages and minimum 0.16% for adult maintenance. Amino acids, including tryptophan, act as building blocks in protein biosynthesis. Tryptophan is a routine constituent of most protein based foods or dietary proteins. It is particularly plentiful in oats, bananas, mangoes, dried dates, milk, yogurt, cottage cheese, red meat, eggs, fish, poultry, sesame, chick peas, sunflower seeds, pumpkin seeds, spirulina, and peanuts. It is also found in turkey at a level typical of poultry in general.
Valine is an alpha amino acid. AAFCO requirements call for a 0.48% Valine content in food for growth and reproduction stages and minimum 0.39% for adult maintenance. Valine is an essential amino acid, hence it must be ingested, usually as a component of proteins. Nutritional sources of valine include cottage cheese, fish, poultry, peanuts, sesame seeds, and lentils.