Basic Horse Nutrition II
By March 31, 2005
Welcome to Kent University study on basic nutritional concepts. In this section we will explain the important nutrients in the diet of animals and cover the basics of balancing the diet of animals.
Nutrition is defined as the study of foods and other components that they contain, and the process of absorbing nutrients from food and utilizing them in the body for growth, maintenance and health.
Before we proceed any further it is important to understand the concept of nutrients. Nutrients are components of foods that have specific functions within the body for growth, maintenance and health. We will study the important nutrients required in the diet of animals.
Nutrients can be categorized into essential and non-essential nutrients. Essential nutrients cannot be synthesized or manufactured by the body in sufficient quantity to meet the body’s needs and must be consumed. Essential nutrients include water, protein (specifically some amino acids), and some minerals and vitamins. On the other hand, non-essential nutrients can be synthesized or manufactured in the body from other components in the diet not necessary.
To help you understand the importance of different nutrients in the diet, we will study each of the important nutrients separately. We will study water, protein, fat, carbohydrates, vitamins and minerals.
Not always thought of as a nutrient, water is a critical nutrient for animals to survive. The body may lose virtually all of its fat, or about half of its protein and live. But a loss of much more than one-tenth of its water can result in death. Water is a major component of blood. Water accounts for 90-95% of blood. Many other tissues contain 70-90% water.
Water performs many important functions in the body including being a transporting agent of nutrients and excretions. Because of its molecular properties, water is involved in many chemical reactions in the body and is a useful solvent. The body uses water to maintain its temperature. Water maintains the shape of cells, without water they would shrivel. In addition to these other functions, water acts as a lubricant for joints and a cushion for organs in the body cavity.
Because water is a very essential nutrient and without it dehydration occurs rapidly, water should be available to animals at all times. This is especially important for animals working hard and during the summer heat.
The next nutrient we will discuss is carbohydrates. Carbohydrates is a term that includes compounds such as simple sugars (glucose and sucrose), starches (long changes of glucose units), cellulose (long chains of glucose units attached such that animals’ enzymes can not break apart the chains), and gums. Carbohydrates are formed by photosynthesis in plants and serve as structural components for the plant. Carbohydrates are a major portion of the animal’s food supply providing much needed energy for the animal’s body. On the other hand, animals store very little energy in the form of carbohydrates in the body. The major storage carbohydrate in the animal’s body is known as glycogen.
The major function of carbohydrates in the animal’s body is to provide energy to the animal. Also, animals use carbohydrates to produce heat in order to keep warm during inclement weather. The carbohydrate molecular structure is used in the animal’s body as a building block for other nutrients. Animals store very little carbohydrate in the body, but convert it to fat, the storage mechanism.
The major categories of carbohydrates in the diet of animals are simple sugars (glucose, sucrose, galactose), starch, and cellulose. Simple sugars are highly digested by simple stomach animals (humans, pigs, chickens, etc) and by beef and dairy cattle. Starch molecules (long chains of glucose units) are broken down by the enzymes in simple stomach animals where the digestibility is medium to high. In beef and dairy cattle, starch is highly digested. Cellulose is made up of long chains of glucose units attached in such a way that enzymes of simple stomach animals can not digest. Whereas, the bacteria in the rumen (large fermentation vat in the four compartment stomach of cattle) can break the bonds of cellulose resulting in high digestibility of cellulose in these animals.
An important part of the diet for animals is the carbohydrate source. In order for the animal to grow or to lactate, it must have energy from a carbohydrate source. In the US, the major grains used for carbohydrates in the diet are corn, oats, wheat, barley, and milo. Animals such as cattle, horses, sheep, goats, llamas, and alpacas can utilize plant materials such as hay, pasture and silages. Plant protein ingredients such as soybean meal, sunflower meal, and canola meal contain starch that can be utilized by all animals.
Of major interest for growing and lactating animals is the nutrient protein. All proteins have one common property, their basic structure is made up of simple units called amino acids. There are some 22 amino acids that can be found in proteins. Proteins are made up of amino acids linked together, similar to chain links. There are many types of proteins with different types of functions. These proteins differ in their arrangement of amino acids in the chain and the length of the chain.
Proteins have many different functions in the body. Proteins are structural components of muscle, cells, skin, hair and hooves. They are functional components of blood serum, enzymes, hormones, and immune antibodies. The hormone insulin, is a protein and has an important role in the absorption of glucose by cells from the blood stream. Many enzymes in the digestive tract are proteins and are important in the digestive process. Should there be an abundance of amino acids in the body, they are broken down and used as an energy source.
It is important to understand a few terms used related to protein. True protein is a protein composed on only amino acids. Every amino acid contains the element, nitrogen. Non-protein nitrogen are compounds not true proteins in nature, but contain nitrogen that can be converted to protein by bacteria. An example of NPN is urea. Urea can be used in the diets of cattle because the microbes in the rumen utilize it to produce true protein. Crude protein or total protein is protein which is composed of true protein and any other source containing nitrogen. Digestible protein is that portion of crude protein in diet that the animal can digest. In simple terms it is the difference of what is present in the diets and what appears in the feces. The digestible protein among ingredients can and does vary.
As was discussed earlier there are approximately 22 amino acids that appear in proteins. Of these 22 some of them are essential amino acids, which are those amino acids essential to the animal and must be supplied to the diet because the animal can not synthesize them fast enough. The number of essential amino acids varies among species of animals. Where as, non-essential amino acids are those that are essential to the animal, but are normally synthesized or are sufficient in the diet and need not be supplemented.
Proteins can be ranked based on how well they provide the needed essential amino acids for the animals. Many measurements have been devised. One such measurement is protein quality, which refers to the amount and ratio of essential amino acids present in the protein.
Dietary protein prior to being utilized by the body must be broken down to simple amino acid fragments for absorption from the digestive tract. Break down of proteins is accomplished by enzymes produced and secreted by cells lining the small intestine and from the pancreas. Once absorbed into the blood stream, amino acids are distributed throughout the body to cells, where they are used by cells to synthesize proteins.
Many different plant products are used as protein sources in animal feeds. These include soybean meal, sunflower meal, canola meal, corn gluten meal, and distiller grains with solubles. Grains used as energy sources in animal diets also include small amounts of dietary protein. By-products from animals are used as protein sources in animal feed. These include meat and bone meal, blood meal, and poultry by-product meal.
Fat is the next nutrient we will discuss. It is a concentrated energy source for animals. A unit of fat produces about 2.25 times more energy than a unit of carbohydrate. Fat sources are insoluble in water. Vegetable fat will float in a glass of water. However, fat is soluble in other inorganic solvents.
The molecular structure of a derived lipid is a glycerol molecule with three fatty acids attached, whereby, it is referred to as a triglyceride. Much has been in the popular press about saturated fat and unsaturated fat. Saturated fat contains fatty acids with less than one double bond in its structure. At room temperature, a fat source containing s significant amount of saturated fatty acids will be a solid (i.e. animal fat). Unsaturated fats, on the other hand, are composed of fatty acids containing two or more double bonds. At room temperature, fat that contains a significant amount of unsaturated fatty acids will be a liquid (i.e. vegetable oils).
In order for the body to utilized dietary triglycerides, they are digested in the small intestine into fatty acid and glycerol. They are absorbed into the body and either used as energy or stored. Fat functions in the body as energy storage, insulation, protection and as a carrier of fat soluble vitamins for absorption. Lipids (fat) serve as components of cell membranes, including skin, hair and nerve tissue. Also, lipids are precursors to some hormones.
Many ingredients used in animal feeds contain a small amount of fat. Major dietary sources of fat used in animal feed products include vegetable oil including corn oil, safflower oil, and soybean oil. Animal fat sources include poultry fat, choice white grease (pork), and beef tallow.
The next nutrient of importance in animal feed is vitamins. These organic substances are required in minute amounts by the animal and are used in many metabolic processes. They are essential for development of normal tissue. While a necessary part of metabolic activity, they are not a part of any structural component in the body.
Vitamins are important for normal reproduction function and healthy skin. Vitamins are involved in vision, blood clotting, and bone formation. Energy utilization involves vitamins. Some vitamins are antioxidants which help protect tissue.
Vitamins are categorized into fat soluble and water soluble vitamins. Absorption of the fat soluble vitamins is facilitated by the absorption of fat from the intestinal tract. The fat soluble vitamins include vitamins A, D, E, and K. Water soluble vitamins include thiamine, riboflavin, niacin, pyridoxine, pantothenic acid, biotin, choline, folic acid, vitamin B12, and vitamin C. Most animals have the capability of synthesizing sufficient vitamin C, except humans and guinea pigs.
Detailing the vitamin requirements of animals is beyond the scope of this program. Many feed ingredients used in animal feeds contain sources of vitamins, but not in sufficient quantities for optimum performance. Because natural feedstuffs are deficient in vitamins for animal needs and most synthetic forms are relatively inexpensive to add, many livestock feeds are supplemented with abundance of synthetic vitamin sources.
The next important nutrient is mineral. Minerals are inorganic, solid, crystalline, chemical elements. You can think of minerals as the rocks in the diet. The total mineral content of plants or animals is called ash. To determine ash content of a feedstuff, a sample is placed in a very hot oven and burned up.
Minerals make up 3-5% of animal body in dry weight. Calcium accounts for nearly ½ of the total body mineral, whereas phosphorus ¼ of the total body mineral. Both calcium and phosphorus are required in the diet to meet the body’s need as well as other minerals. Minerals can not be synthesized in the body by ordinary chemical reactions.
Minerals required in the diet by animals are classified in two categories – macro and trace minerals. As the name indicates, the macro minerals are present in greater concentrations in the body or are required in the diet in larger quantities than trace minerals. Macro minerals include calcium, chloride, magnesium, phosphorus, potassium, sodium, and sulfur. An alphabetical list of trace minerals includes cobalt, copper, fluorine, iodine, iron, manganese, molybdenum, selenium, and zinc.
The major function of minerals is skeletal structure – bones contain significant amounts of calcium and phosphorus. Minerals are also involved in water balance and enzyme activity – for some enzymes to be active they require a mineral as a part of their structure. Other functions include nerve function, components of amino acids, and oxygen transfer. Iron is a component of hemoglobin which carries oxygen in the blood.
Elemental minerals do not appear in nature in great abundance. Typically minerals are found in nature as a compound. These compounds are used as sources of minerals in the diet. For example, very little elemental calcium is found in nature, but is found as calcium carbonate. This is true for other minerals also. Listed in this slide are typical sources of minerals used in animal diets. This is not a complete list of mineral products that can be used as mineral sources. For example, as a source of copper, copper sulfate or copper oxide can be used. However, the copper in copper oxide is not as available to the animals as copper sulfate.
One of the functions of the diet is to provide energy for the animal. By definition energy is the capacity to do work. Feedstuffs furnish energy for body processes including digestion/metabolism, body temperature, maintenance, activity, and reproduction. There are several ways to express energy; most common in the US is calorie. One calorie is defined as the energy required to raise 1 gram of water from 14.5ºC to 15.5ºC. One thousand calories is equal to one kilocalorie, the most common term used in describing energy for a feedstuff.
The total amount of energy in a feedstuff (gross energy) is unavailable or unusable by animals. Parts of the energy in feedstuffs are lost in the feces, urine, heat production. The amount lost is different for each feedstuff. Consequently, animal nutritionists partition the energy of each feedstuff to provide a truer picture of the amount of usable energy in a feedstuff. Unfortunately, these fractions of energy can not be determined with an easy laboratory test. Elaborate research trials have been devised in past years to determine each fraction of energy. For swine metabolizable energy is typically used as the measure of energy for feed stuffs, whereas, beef and dairy utilize the net energy.
Protein, carbohydrates, and fat serve as energy sources to animals. Typically fat contains 2.25 times more energy per unit than carbohydrates.
The key concept for formulating a diet for an animal is balancing the nutrient concentrations in the diet for optimal growth and reproduction. In the past, there has been talk that we could cram all the nutrition required into a pill – a pill does not provide satiety or satisfaction to the animal. On the other hand, if the animal is allowed to free-choice feedstuffs, it does not always make the right choices to maximize performance. Based on scientific trials, we can determine the optimal balance of nutrients in the diet for optimal growth or in the case of an adult dog, maintain a healthy weight.
To balance the diet, we must remember that animals eat to meet their energy requirement in the case of growing animals. For adults, they tend to over eat, so limiting their intake is the best option.
In general terms, the nutrient balance revolves around the energy content of the diet. The energy content of the diet can dictate the feed or food intake amount by an animal. For example, an animal will eat less of a high-energy diet compared to a low-energy diet to meet its energy needs. For the lower intake, the concentration of the vitamins, minerals, and protein should be higher to ensure sufficient intake of these nutrients.
An animal’s diet must contain essential nutrients to optimize growth and health of the animal. Animals essentially eat to meet their energy needs. The energy content of the diet is a factor that determines how much the animal will consume and the required quantities of essential nutrients. Animals can derive energy not only from carbohydrates and fat, but also protein.
It is important that the diet include protein sources that provide quality protein (amino acid balance) for optimizing growth and maintenance of the body’s structural components, such as muscle tissue and organs, and functional components such as enzymes, antibodies and hormones. Fat is energy-dense, and fatty acids (components of fat) are important for immune function, hormones, and skin and coat health.
Carbohydrates are the most cost-effective energy source in the diet and vary greatly in digestibility and utilization between ruminant and simple-stomached animals. Vitamins and minerals must not only be available in sufficient quantities in the diet, but must be in optimal balance for beneficial health effects. Fresh clean water is critical for animal health and life.