The Components of Feed
Every single feed is made up of the same components but in different amounts. This section aims to define the function of each nutrient and explain how this affects the way in which we feed our horses
Carbohydrates are a group of organic compounds essential for providing the following:
Energy for vital systems such as breathing and muscle contraction.
Fuel for warmth, growth and body development.
Carbohydrates are found in plants where they are produced by the action of photosynthesis on water and carbon dioxide. Hence carbohydrates are made up of the elements carbon, hydrogen and oxygen. Carbohydrates can be split into two categories, structural carbohydrates (e.g. cellulose as found in grass and other forage) and non-structural carbohydrates (e.g. sugars as found in molasses and starches as found in cereals).
Sugars and starches are digested in the small intestine. The products of digestion are used for energy and any excess is stored as glycogen in the liver from where it is retrieved when necessary.
Cellulose is insoluble and cannot be digested by the horse itself. It is broken down by the bacteria which live in the large colon and caecum to enable the horse to make use of it as a food.
Fibre, of which cellulose is a large constituent, is essential for the digestive tract of the horse to function normally. It stimulates peristalsis and slows down the rate at which food passes through the digestive tract allowing greater absorption of nutrients.
The article "Hay Types for Performance Horses" by Antony Jones will give you a further insight into the digestion of fibre.
Proteins are used for growth (particularly in young animals), body building and tissue repair. They are made up of amino acids which act as small building blocks which are chemically linked together in different ways to make different proteins. There are around 20 amino acids and approximately half of these can be synthesised in the body. The remainder are known as the essential amino acids and they must be provided in the diet. The best known essential amino acids are lysine and thymine .
Proteins are produced by plants through photosynthesis using a combination of nitrogen extracted from the soil, carbon, hydrogen and oxygen. If the diet is deficient in protein the animal will be in poor condition with a dull coat and poor muscle development. Excess protein is stored as fat and excreted via the urinary system.
Peas, beans, clover and alfalfa all contain high levels of protein.
Fats and Oils are a terrific source of of energy for the horse as they contain high levels of calories. This is particularly useful when making up diets for endurance horses and three-day eventers as they can be used to substitute for some of the starch in the diet making the ration less bulky. They are also important for a number of functions:
Energy to maintain the body temperature and also to provide an insulating subcutaneous layer.
Growth of cells, membranes and hair.
Lubrication in joints and tissues.
Involved in body metabolism e.g.. the conversion of one substance to another.
Fats and oils are also a valuable source of vitamins and minerals. Fats and oils are found in vegetable and linseed oil as well as oats, barley etc.
Vitamins are required for all the normal metabolic functions of the horses body. Vitamins can be divided into two main categories, fat soluble (A, D, E and K) and water soluble (B and C). Fat soluble vitamins can be stored in the body whilst water soluble vitamins cannot. It is therefore possible to provide an excess of fat soluble vitamins which can be toxic.
Vitamin A (retinol) is required for vision, normal skeletal development, fat and carbohydrate metabolism and reproduction. Deficiency causes poor growth, weight loss, increased susceptibility to respiratory infection, lameness, infertility and keratinisation of the skin and corneas. Vitamin A is derived from a chemical called beta-carotene which is found in grass and forages.
Vitamin D (calciferol) is required for the metabolism of calcium and phosphorus and hence for bone development and maintenance. Both deficiency and excess cause swollen joints, skeletal abnormalities and lameness and an excess may also cause bone to be laid down in soft tissue. Vitamin D is produced by the action of sunlight on the skin. Colostrum is a rich source of Vitamin D.
Vitamin K is necessary for the clotting of blood. Vitamin K deficiencies are rare as it is synthesised by the bacteria of the gut. Vitamin K can be stored in the body and is commonly found in leafy plants.
Vitamin E (tocopherol) is actually a group of closely related substances. Vitamin E acts as a non-specific biological anti-oxidant and works with selenium to act as a body tissue stabiliser. It is required by the reproductive system, muscle tissues, the vascular system and red blood cells. Deficiency causes a wide range of problems including fragility in red blood cells and infertility. Vitamin E is commonly found in green fodder, alfalfa and cereal grains.
Vitamin B A number of substances make up the Vitamin B complex. The B group are essential for the utilisation of food and the correct functioning of the nervous system. Most of this group are produced by the action of bacteria on green foods and forage in the hindgut though some are found in food. The feeding of antibiotics may affect the body's ability to synthesise vitamins usually produced by the bacteria in the gut.
One of the most important of the B Vitamins is Biotin as described further in this article by Antony Jones.
Vitamin C (ascorbic acid) is required for the correct functions of the blood and blood vessels in conjunction with iron and copper. It also plays a part in the defence mechanisms of the horse. Vitamin C is also produced by the bacteria in the hindgut of the horse and is also found in green fodder and grass. Deficiency causes skin problems, weight loss and oedema.
Minerals are inorganic compounds which are required for all the functions of the body, from energy production to hoof and hair growth. Minerals are split into two categories; major elements and trace elements
Calcium (Ca) is required for bone growth, maintenance and development, blood coagulation, lactation, nerve and muscle function and as an enzyme activator and inhibitor. A calcium deficiency has been implicated in Developmental Orthopedic Disease and the onset of Equine Rhabdomyolsis and also causes an increased blood clotting time. Calcium is found in leafy green foods especially legumes such as alfalfa. Cereals are poor sources of calcium and therefore horses on high cereal diets may require calcium supplements.
Phosphorus (P) works closely with calcium in bone and is also required for energy metabolism. Deficiency can cause bone abnormalities and subnormal growth in young horses. Phosphorus is commonly found in cereal grains such as oats.
The Calcium:Phosphorus ratio This ratio is very important as it affects the ability of the horse to obtain the necessary nutrients from his feed. The ideal ratio is between 1.6 : 1 and 2 : 1.
Magnesium (Mg) is associated with Calcium and Phosphorus in the metabolism of bone, plays a part as cofactor and activator for the enzymes of the metabolic pathways for proteins, fats and carbohydrates and is required for normal cell metabolism and nerve and muscle function. A deficiency can cause mental apprehensiveness and excitement and muscular spasms and twitching. Magnesium is commonly found in alfalfa, clover, bran and linseed.
Potassium (K) is required for the regulation of body fluids, nerve and muscle function, carbohydrate metabolism and maintenance of the acid-base balance. Potassium is found in grass and conserved forage, therefore deficiency is very rare.
Sodium (Na) is required for the maintenance of the acid-base balance, for body fluid regulation, nerve and muscle function and carbohydrate metabolism. Deficiency causes dehydration, poor growth and reduced utilisation of digested proteins and energy. The majority of natural foods are low in sodium, therefore the diet may be supplemented with common salt usually in the form of a salt or mineral lick.
Chlorine (Cl) is closely associated with sodium and potassium and is involved with the regulation of body fluids. The horse is unlikely to be deficient in chlorine provided the demand for sodium is met.
Copper (Cu) is required for the formation of bone, cartilage, elastin and hair and is also involved in the formation of haemoglobin and red blood cells. Deficiency causes anaemia, poor growth, hair depigmentation and weight loss. Copper is found in most foodstuffs particularly seeds.
Zinc (Zn) is required for normal cell metabolism and as an enzyme activator and antagonist. Deficiencies are rare, but may cause reduced appetite and eight loss. Zinc is found in yeast, bran and cereal germ.
Manganese (Mn) is required for the activation of enzymes and is also involved in the formation of cartilage.
Selenium (Se) is fully described in the article "Selenium and the Horse" by Antony Jones
Cobalt (Co) is required for the synthesis of vitamin B12 in the gut and the activation of enzyme reaction. Deficiency results in anaemia, reduced growth and weight loss. Cobalt is found in most foods.
Iodine (I) is required for reproduction and hormone synthesis. A deficiency results in abnormal cell reaction rates and may cause mares to have abnormal oestrous cycles or weak foals. Trace levels of Iodine are found in most foods.
Iron (Fe) is required for normal haemoglobin and red blood cell production and therefore a deficiency causes anaemia. Iron is found in most natural foods, so deficiency is unlikely.
Sulphur (S) and Fluorine (F) are also trace minerals
Water is probably the most vital nutrient in the diet. It is present in every cell in the body and is required for all the chemical and physical processes which maintain life. The body of an adult horse is 60 - 70% water and although a horse can survive losing almost all his body fat and up to around half his body protein, a 20% loss of water can be fatal.
A horse will drink up to 55 litres or 12 gallons of water a day depending on temperature, health, work, milk production, diet and loss of water through sweat, droppings and urine. It is essential that fresh, clean water should be available at all times.
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Updated: October 2005.