Written by Dr. Jill Cline, Ph.D.
To maintain health and vitality throughout life, dogs require a diet that provides all of the essential nutrients in their correct quantities and proportions. Feeding your dog an appropriate food supports normal gastrointestinal tract functioning, produces a lustrous coat and healthy skin condition, and contributes to ideal body condition and muscle tone. Understanding the functions of the major nutrients can help you to select the best food for your dog’s age and lifestyle.
Important Nutrients to Consider with Dogs
Protein: Dietary protein is necessary for the growth and maintenance of almost all tissues of the body. Within the body, protein is a major structural component of hair, skin, tendons, ligaments and cartilage. Enzymes that catalyze essential metabolic reactions, hormones that act as the body’s chemical messengers, and antibodies that comprise the immune system are all proteins. The body’s protein stores are not static, but rather are in a constant state of flux, as cells and tissues wear out and are replaced. The diet provides a regular supply of new protein to replace these normal losses. Any dietary protein that is not used for structural or metabolic functions can also be used as an energy source.
The Dog’s Protein Requirement: An optimal level of protein is needed in your dog’s diet throughout life, and is especially important during growth and development. Maintaining the body’s protein reserve is also essential as dogs age to promote normal turnover and support the immune system. High quality commercial dog foods are specifically formulated to meet dogs’ daily protein needs. Dietary protein should contribute a minimum of 20 % to 25% of the calories in foods formulated for adult dogs and at least 25 % of the calories in foods formulated for growing puppies (Box 1). Although overt protein deficiency is uncommon in dogs, it can occur if an inadequate diet is fed. Signs of protein deficiency in dogs include depressed appetite, impaired growth, weight loss and the development of a rough and dull hair coat. Because sufficient dietary protein is required for a healthy immune system, dogs who are fed diets that are marginal or low in protein may have compromised immune system function, leading to enhanced susceptibility to infection and disease.
PERCENT PROTEIN REPORTED ON GUARANTEED ANALYSIS PANEL THAT
CORRESPONDS TO 20 AND 25 % PROTEIN CALORIES
Fat Content of Food* 20% of calories as protein 25% of calories as protein
7% (low fat) 17 22
12% (moderate fat) 19 24
22% (high fat) 21 27
* As % fat increases, the food’s energy density increases
Amino Acids: Amino acids are the basic units of proteins and are linked together by peptide bonds to form long protein chains. Protein that is consumed in the diet is digested by the body into its component amino acids, which are then absorbed into the body. Like other animals, the dog has a metabolic requirement for 22 amino acids. However, 12 of these, the nonessential amino acids, can be synthesized by the body in adequate amounts to meet needs. The remaining 10 amino acids, called the essential amino acids, cannot be made by the body in sufficient amounts and must be supplied by dietary protein (Box 2).
ESSENTIAL AMINO ACIDS FOR DOGS
Histidine Methionine Phenylalanine
Isoleucine Leucine Tryptophan
Arginine Valine Lysine
Dietary Fat and Essential Fatty Acids: Dietary fat provides a concentrated source of energy, contributes to food texture and palatability, allows for the absorption of fat-soluble vitamins, and provides essential fatty acids. Similar to amino acids, fatty acids can be classified as either nonessential or essential. Essential fatty acids have a number of important functions in the body (Box 3). Although at least two fatty acids are essential for health (linoleic acid and arachidonic acid), the dog requires only linoleic acid in the diet. If an adequate level of linoleic acid is provided in the diet, dogs can produce enough arachidonic acid from this fatty acid to meet their needs. Linoleic acid is found in both plant and animal products such as corn oil, soybean oil, beef tallow and chicken fat.
Omega-6 Fatty and Omega-3 Fatty Acids: Fatty acids can also be classified according to their chemical structure. The two classes that are of greatest importance to
dogs’ nutrition and health are the omega-6 fatty acids and the omega-3 fatty acids. Linoleic acid and arachidonic acid are both omega-6 fatty acids. Omega-3 fatty acids include several long-chain omega-3 fatty acids, such as Docosahexaenoic acid (DHA) and eicosapentaenoic acid (EPA) that are found in fish oil. Although they are not classified as essential fatty acids, the omega-3 fatty acids have important functions in the body that contribute to dogs’ health and vitality. For example, increasing the proportion of omega-3 fatty acids in the diet helps to modulate the immune response and is helpful in managing certain types of inflammatory disorders in dogs. Recent research also indicates that DHA is important for development of the nervous system and vision.
FUNCTIONS OF ESSENTIAL FATTY ACIDS IN THE BODY
• Maintain healthy skin and hair coat
• Aid in the immune system’s response to injury and infection
• Promote normal blood clotting
• Help in the regulation of blood flow to body tissues
• Support normal reproduction
Carbohydrate and Dietary Fiber: Digestible carbohydrate is an important source of energy in the dog’s diet. Several types of cooked starch that are included in commercial dog foods are well utilized by dogs and provide an excellent energy source. Dietary fiber is a collective term used to describe the parts of plants that are poorly digested by the body. Like humans, dogs do not have a dietary requirement for fiber per se. However, the inclusion of optimal amounts of fiber in dogs’ diets has numerous benefits. Insoluble fiber provides dietary bulk, contributes to satiety and helps to maintain normal gastrointestinal motility while soluble fiber is an important contributor to the normal gastrointestinal function and to the health of cells lining the intestinal tract.
Essential Minerals: Minerals are inorganic elements that are needed for the growth, development, and maintenance of all of the body’s systems. Macrominerals are those essential minerals that are found in greatest quantity in the body. These include calcium, phosphorus, magnesium, sulfur and the electrolytes sodium, potassium and chloride. The microminerals (also called trace elements) are also essential for health but are needed in very small amounts. (Box 4 provides a summary of the primary functions of the major essential minerals in the dog’s diet). Today, mineral deficiencies are rare in dogs. When problems do occur, they are usually due to dietary imbalances in which one or more minerals are supplemented in excess of others or when a mineral imbalance occurs secondary to an underlying illness.
FUNCTIONS OF ESSENTIAL MINERALS
Calcium and phosphorus: Necessary for skeletal growth and maintenance, blood clotting, and nerve and muscle function. A dietary ratio of calcium: phosphorus of 1.0 to 1.5 parts calcium to 1.0 part phospho¬rus is optimal
Magnesium: Component of the skeleton; necessary for muscle contractions and nerve impulse transmission
Sulfur: Needed for maintenance of healthy cartilage; necessary for synthesis of the hormone insulin and the blood clotting agent, heparin
Electrolytes – Sodium, Potassium, Chloride: Regulate body fluids and acid-base balance; necessary for nerve transmission, muscle function, and energy metabolism
Iron: Component of the oxygen-carrying proteins, hemoglobin and myoglobin; component of enzymes involved in cellular use of energy
Copper: Needed for formation and activity of red blood cells, required for normal pigmentation of hair and skin
Zinc: Acts a co-factor in many enzymes and is necessary for normal nutrient metabolism; needed for healthy skin and hair growth
Cobalt is a component of vitamin B12
Iodine is an essential component of thyroid hormones
Manganese is needed for nutrient metabolism and cartilage formation
Selenium is necessary to protect cells from damage due to oxidation
Vitamins: Vitamins are organic molecules that are needed by the body in very minute amounts, but are essential for health. Vitamins have a wide variety of functions in the body and are typically classified into two groups: fat-soluble vitamins and water-soluble vitamins. The fat-soluble vitamins, A, D, E and K, can be stored in the body. The water-soluble vitamins include the B-complex vitamins and vi¬tamin C. They are not stored in any appreciable amount in the body and so must be supplied daily in the diet (Box 5).
Water Requirement: Although is it easily overlooked, water is the most important essential nutrient for all animals. This is not surprising given that most tissues in the body are comprised of between 70 and 90 percent water! Within the body, water acts as the solvent for all cellular reactions and provides the transport medium for nutrients and wastes. Water is also important for regulating body temperature and for normal food digestion and metabolism. Your dog should always have free access to fresh clean water throughout the day.
Feeding Dogs for Health and Longevity
Every dog owner wishes to provide the best possible care for their dog. A primary component of good care is feeding a high quality dog food that has been formulated specifically to meet the essential nutrient needs of dogs. In addition, every dog must be fed as an individual. Puppies and highly active dogs have somewhat different nutritional needs than do sedentary adult dogs or elderly dogs. Similarly, while some dogs enjoy snoozing for a good part of the day on the couch, others are, by nature, more “high energy” companions. For these reasons, the best way to provide your dog with the nutrition that will support optimal health throughout life is to select a high quality dog food that has been specifically formulated for your dog’s current age, life stage and lifestyle.