Dog Nutrition Basics
Your pet’s nutritional health depends on receiving the correct amounts and proportions of nutrients from the six required groups: water, protein, fat, carbohydrate, minerals and vitamins. With the exception of water, commercial dog and cat foods identified as 100% complete and balanced contain all of these required nutrients.
Water is essential in helping regulate body temperature, lubrication of body tissues and as a fluid medium for the blood and lymph systems. Because water is involved in practically every reaction within an animal's body, any large deviation will be associated with adverse effects. Dogs and cats, therefore, have several systems designed to maintain constant water balance. Indeed, cats have the ability to also concentrate their urine thus sparing water loss.
Water intake is controlled by thirst, hunger, metabolic activity (work, gestation, lactation, growth), and the environment (humidity and temperature).
Dogs and cats obtain water from the water they drink, fluid ingested with food, and water generated from metabolic processes in the body. Water is primarily lost in urine, feces, and respiration.
A dog's water requirement is determined in large part by the amount of food they consume each day. A general guideline is that dogs require 1 ml of water for each kcal of energy. For cats, this number is lower, but there are indications that increasing water intake is beneficial in cats as it may reduce the risk of lower urinary tract disease. For nursing females, the water requirement will be increased to support milk production. Water should always be freely available for your dog and cat.
Energy is measured in calories and a calorie is defined as the amount of heat required to raise the temperature of one gram of water from 14.5 degrees Celsius to 15.5 degrees Celsius. Because this amount of heat is so small, it is common to describe energy requirements and the energy content of foods in kilocalories (1000 calories = 1 kcal). The term Calorie, written with a capital C, is often used to refer to the amount of energy in 1 kilocalorie of food.
Food and Water Consumption
When the water content of a diet increases, the dog or cat usually drinks less water. Therefore, dogs or cats consuming canned diets, which contain approximately 70-75% water, will generally drink less water than dogs consuming dry diets, which contain about 8-12% water.
Protein is an essential nutrient and serves numerous functions in the body, including but not limited to, muscle growth, tissue repair, enzymes, transporting oxygen in the blood, immune functions, hormones and as a source of energy. Proteins are made up of amino acids, thus amino acids are the building blocks of proteins. Each protein has a unique combination of amino acids that contributes to its molecular shape and function. Dietary protein that is digested in the stomach and small intestine is broken down to peptides (smaller pieces of the protein containing two or more amino acids) and free amino acids which are then absorbed into the bloodstream. Amino acids are distributed to various cells of the body where they are utilized to build body proteins.
More than 20 amino acids are involved in the synthesis of protein in the body. Essential amino acids are those that cannot be formed fast enough or in sufficient amounts to meet the requirements for growth and maintenance and, therefore, must be supplied in the diet. Nonessential amino acids are those that the body can produce in sufficient amounts from other nutrients and metabolites and, thus, do not need to be supplied in the diet.
Although essential amino acids are not stored as such in the body for any significant period of time, they are constantly metabolized. Consequently, they must be provided simultaneously in the proper proportions in a pet's diet. Cats and dogs have the same requirements for the same 10 essential amino acids. However, cats also require taurine.
- taurine (required in cats)
Sources of Protein
Protein is derived from both animal and plant sources. Most protein ingredients contain inadequate amounts of one or more amino acids and are thus inefficient if used as the sole source for meeting protein needs. However, by careful selection and combination of different protein sources, these inefficiencies can be completely overcome. For example, soybean meal and corn complement each other perfectly, because the amino acids which are deficient in one are present in the other. Neither meat nor soybean meal is an ideal source of protein; however, either can be adequate if fed in combination with another complementary source of amino acids.
To appropriately evaluate the protein levels of different dog and cat foods, two factors should be considered. One is the level of protein and the other is the protein digestibility, or availability of the protein to a dog or cat, which can be determined only by controlled feeding studies. Two diets may have the same protein level listed on their packages, but the results of from digestion studies may indicate very different levels of protein digestibility. For example, a dog food which contains 21% protein with 85% digestibility would deliver equal amounts of protein as a diet containing 23% protein with 78% digestibility.
In addition to the protein level, quality control during processing of dog foods is important. Protein may be damaged by excessive heat processing, but most reputable dog food manufacturers use proper cooking methods and employ quality control measures to ensure that products are made properly. Because information about protein digestibility is not listed on dog food labels, the manufacturer's reputation is important. All of our foods are highly digestible.
Excesses and Deficiencies
In dogs and cats fed diets containing more protein than is needed, extra protein is metabolized and used for energy. Unlike fat, there is a limit to the amount of protein stored as such in the body. Once the demand for amino acids is met and protein reserves are filled, protein energy could potentially go to the production of fat.
Protein is an essential nutrient. Dogs and cats fed diets too low in dietary protein may develop signs of deficiency. These may include a depressed or decreased appetite, poor growth, weight loss, rough and dull haircoat, decreased immune function, lower reproductive performance, and decreased milk production. Dogs can also experience subclinical protein deficiencies. In such a condition, they may appear perfectly healthy, yet they may be more susceptible to infections and other environmental stresses. Such deficiencies are rare if you pet if fed a complete and balanced diet.
Carbohydrate sources are sugars, starches and dietary fiber. Simple sugars are the smallest carbohydrate molecules and are easily digested and absorbed. By contrast, complex carbohydrates, or starches, are combinations of simple sugars forming long chains which require more digestion before they can be absorbed into the bloodstream. Dietary fibers are carbohydrates which are not digestible by dogs or cats.
In manufactured pet foods, most dietary carbohydrates are grains, such as wheat, corn and rice.
The primary site of carbohydrate digestion is in the small intestine, where these complex compounds are broken down to glucose (a simple sugar). Glucose is the normal source of energy used by most cells in the body.
When dogs and cats consume diets containing more energy than is needed, excess carbohydrate energy is stored in the form of glycogen in the liver and muscles and is converted to fat and stored in adipose tissues. During periods of fasting, stress or exercise, glycogen is broken down to glucose and delivered to the bloodstream where it is distributed to all body tissues.
The primary function of carbohydrates is to provide energy.
Carbohydrates in dog and cat food
Carbohydrate may make up 40 to 55% of dry diets in dog food and is found in lesser amounts in typical cat foods. A large portion of the carbohydrate in pet foods is derived from grains. Grains are usually processed by grinding, flaking or cooking. These processes improve palatability and digestibility. Raw or improperly cooked starches are poorly digestible, so careful processing is important to make highly digestible pet foods.
Here is a list of some common sources of digestible carbohydrate found in dog and cat foods:
Cereal Grain or flour from:
The bran or hulls from grains and other vegetable products provide some common sources of dietary fiber in pet foods:
- Soybean hulls
- Wheat bran
- Beet pulp
- Rice bran
- Oat bran
- Pea fiber
Fat is a concentrated form of energy. Compared to protein and carbohydrate, fat contains approximately two and a half times the amount of energy per gram. Most dietary fat is made up of triglycerides, which is a group of three fatty acids linked to a glycerol backbone. Fatty acids can be classified by the length of their carbon chain, by the presence or absence of double bonds, the number of double bonds, and the position of those bonds along the carbon chain.
Fat with no double bond at all are called saturated fats. Fat containing fatty acid chains with a double bond are called unsaturated fat. These may vary from a single double bond in the fatty acid molecule (monounsaturated) to fatty acids with many double bonds (polyunsaturated). Saturated fat is generally solid at room temperature and unsaturated fat is usually liquid.
Fat digestion is more complex than that of protein or carbohydrate. Still, healthy dogs and cats digest fat with great efficiency, approximately 90-95%.
In addition to being a source of energy, fat is needed as a source of essential fatty acids. The polyunsaturated essential fatty acids are important for normal skin and hair coat, normal immune function, and many other aspects of health.
Minerals are relatively simple molecules compared to other nutrients which can be large and complex. Nutritional issues related to minerals include the amount of each in the diet, proper balance of all minerals, and the availability of minerals in the dog's food.
Minerals perform many different functions in the body such as bone and cartilage formation, enzymatic reactions, maintaining fluid balance, transportation of oxygen in the blood, normal muscle and nerve function, and the production of hormones. While the function of some minerals can be separated from that of others, it is impossible to adequately nourish a dog without providing all the minerals in their proper proportions. This is due to the fact that minerals interact in many aspects of body function and maintenance.
Supplementation of any one mineral to an otherwise balanced diet can create imbalances and possibly disrupt an animal's nutritional health. Manufacturers producing good quality dog foods maintain a safety margin for all essential nutrients in the product formulation to compensate for any loss during normal processing and storage and for the variation in the needs of individual dogs.
The minerals are usually grouped into macro and micro categories. Macro-minerals are needed in greater amounts in the diet, and found in larger amounts in the body than micro-minerals.
- Calcium (Ca)
- Phosphorus (P)
- Sodium (Na)
- Chloride (Cl)
- Potassium (K)
- Magnesium (Mg)
- Iron (Fe)
- Zinc (Zn)
- Copper (Cu)
- Manganese (Mn)
- Selenium (Se)
- Iodine (I)
Calcium and phosphorus are essential minerals and are necessary for normal bone development, as well as numerous metabolic functions. These minerals provide rigidity to bones and teeth, aid in normal blood coagulation, aid in controlling passage of fluids through cell walls, and are necessary for nerve excitability.
Sodium and chloride serve largely as fluid-regulating minerals to help maintain the balance between fluids inside and outside individual cells of the body. Sodium aids in the transfer of nutrients to cells and the maintenance of water balance among the tissues and organs.
Chloride is required for the formation of hydrochloric acid (HCl) in the stomach, which helps in the digestion of protein, and in maintaining acid-base balance throughout the body.
Potassium is found in high concentrations within cells and is required for proper enzyme, muscle and nerve functions, as well as helping to maintain fluid balance throughout the body. Potassium is widely distributed in foodstuffs and deficiencies in the diet are not likely when dogs and cats are fed complete and balanced dog foods. Like sodium and chloride, potassium deficiency can occur in the case of chronic diarrhea and/or vomiting or other illness.
Magnesium is important as a structural component of both muscle and bone, and it plays a key role in many enzymatic reactions throughout the body. Some attributes of magnesium are also common to calcium, potassium, and sodium. Calcium and phosphorus influence magnesium balance, because high amounts of calcium or phosphorus decrease the absorption of magnesium from the intestinal tract.
Although the total body content of iron is small (only about 0.004%), it plays a central role in life processes. A small amount of iron (heme) combines with a large protein (globin) to make hemoglobin, the oxygen-carrying compound in red blood cells. Iron is also an important component of the enzymes needed for energy utilization.
Iron is absorbed primarily from the small intestine. The absorption of this mineral is rapid. Red blood cells and their hemoglobin are constantly being destroyed and replaced throughout life, especially during growth, so an adequate supply of iron is essential.
Zinc is important in the production of proteins and a functional immune system, as well as for DNA and cellular turnover. Some 300 enzyme systems are also dependent upon zinc, including enzymes which protect cells from damage caused by oxidation. Zinc is present in natural feedstuffs and can be added as zinc salts or other complexes into complete pet foods.
Manganese is an essential element for many animal species. The name, manganese, is derived from Latin for a form of magnetic stone, magnesia.
Manganese occurs in the body principally in the liver, but it is also present in appreciable amounts in the kidney, pancreas and bone. The lowest concentrations are found in skeletal muscle. Despite the small total supply in the body, this element has several essential functions involving protein and carbohydrate metabolism and reproduction. More specifically, manganese is thought to be an activator of enzyme systems involved in the production of energy, fatty acid synthesis and amino acid metabolism. The functions of manganese, copper, zinc and iron may be interchangeable in certain enzyme systems.
Copper is another mineral that is important for energy metabolism and oxygen transportation in the bloodstream. Copper absorption is generally greater (60 to 70%) in younger animals than in older animals (10 to 20%). This mineral is absorbed in the stomach and small intestine, and stored primarily in the liver, kidney and brain. The availability of natural dietary copper is reduced by phytates, by high levels of ascorbic acid (Vitamin C), by increased levels of calcium, zinc, iron and sulfur, and by some toxic metals such as cadmium, silver or lead.
The functions of copper in the body are quite varied because it is involved in collagen and elastic connective tissue formation, the development and maturation of red blood cells, antioxidant functions, as well as providing pigmentation for hair and wool.
Selenium. This trace element was one of the few nutrients to be identified as a toxic substance long before it was found to be an essential nutrient for animals. Although selenium is required in the smallest amount of any of the generally accepted trace elements, it is also the most toxic if consumed in excess. Selenium works in conjunction with Vitamin E to act as an antioxidant in the body and is necessary for normal immune function. Selenium is usually added as a separate ingredient in commercial pet foods to assure an appropriate supply.
Iodine is critical for the production of thyroid hormones by the thyroid gland. The primary function of these hormones is to regulate and influence basal metabolic rates of the body (for example, how quickly an animal metabolizes or burns up energy after eating a meal). Without the thyroid gland, or the adequate function of these hormones, a dog would exhibit poor growth, hair loss, weight gain and extreme weakness.
The scientific recognition of the existence of vitamins at the beginning of the 20th century resulted from the efforts of a number of researchers working independently in several countries. They recognized that diets composed of purified ingredients were not able to support the life of experimental laboratory animals and had the curiosity to find out why. The isolation of vitamins and the definition of their functions in the body, the discovery of the therapeutic value of minute quantities and the nutrient profile of ingredients with respect to vitamins have profoundly affected animal (and human) nutrition.
Compared to the other groups of nutrients, vitamins are required in the smallest amounts. And unlike minerals, vitamins are complex substances. Vitamins are classified as either fat-soluble (Vitamins A, D, E, K) or water-soluble (B-Vitamins and Vitamin C). Fat-soluble vitamins depend on the presence of dietary fat and normal fat absorption for their uptake and utilization in the body.
Like so many of the other nutrients discussed thus far, vitamins work in concert with other vitamins and nutrients to nourish the animal. This makes it important to provide balanced amounts of vitamins and other nutrients in complete diets. Adding supplements to diets which are already complete and balanced may create imbalances with detrimental effects.
Vitamin A has been the subject of much research in the fields of animal nutrition and veterinary medicine. Vitamin A has a number of functions necessary for the health and well-being of animals, including a role in normal vision, growth, immune system function and reproduction. In addition, Vitamin A and its precursor, beta-carotene, have antioxidant functions. The plant source of Vitamin A is beta-carotene, which animals must convert to the actual vitamin before it becomes active and function as Vitamin A.
Although Vitamin D (cholecalciferol) is considered a vitamin, it is also considered to have hormone-like activity and is one of three major hormones involved in the regulation of calcium in the body. Its primary functions are to help in the mineralization of bone and to increase the absorption of calcium and phosphorus from the intestine. Vitamin D can be acquired in the diet, or, in most species, it can be produced in the skin following exposure to ultraviolet radiation from sunlight.
Vitamin E is used to describe a family of chemical compounds called tocopherols, derived from the Greek words meaning child-bearing, which refers to its role in reproduction. It is also known for its action as a biological antioxidant. Tocopherols are found in plant oils, particularly in association with the polyunsaturated oils from seeds such as safflower and wheat germ, or soybean oil. Lack of Vitamin E in the diet could result in damage to the wall or membrane of cells throughout the body. As a nutrient, Vitamin E works in conjunction with other nutrients and compounds (selenium, a micro mineral, and glutathione, an amino acid-derived compound) as an antioxidant to minimize damage to cells from oxidation.
Some tocopherols are more active in the body than others. The alpha form of the vitamin is the most active as a nutrient, and it is the compound added to food to meet the animal's dietary requirement. When Vitamin E is used as a preservative, mixtures of several forms of tocopherol are added to help prevent oxidation of the fat in the diet. The form of tocopherol most effective at preventing oxidation of fat in foods has low biological activity in the body and is not considered part of the nutrient content of the diet.
There is no known toxicity due to oral ingestion of even moderately high amounts of Vitamin E in animals. Good quality commercial pet foods contain adequate amounts of this vitamin to meet the dog and cat’s dietary needs.
Vitamin K was the last of the four fat-soluble vitamins to be discovered. The most common forms of Vitamin K in the diet are called menadione and phylloquinone, which come from green, leafy plants and vegetables. The major function of this vitamin is as a clotting agent in the blood.
B-complex vitamins are those vitamins originally identified as B1, B2, B6, B12 and others which are listed below. These vitamins are required in small amounts in the daily diet and are essential to many functions in the body. Although these nutrients don't provide energy in and of themselves, they are critical in the metabolism of protein, carbohydrate and fat, which results in energy for body processes. Unlike the fat-soluble vitamins, the B Vitamins are not stored to any extent in the body and must be consumed daily.
Water-Soluble B Vitamins include:
- Thiamine (B1)
- Riboflavin (B2)
- Pantothenic acid
- Pyridoxine (B6)
- Vitamin B12
- Folic acid
Vitamin C (Ascorbic Acid) is also a water-soluble vitamin and has a primary metabolic role in the body of all mammals involving the synthesis or production of collagen. While ascorbic acid is essential in the diet of humans, other primates and guinea pigs, dogs have no dietary requirement for this vitamin since they make their own.