Protein
Protein is important for body building and tissue repair. Protein is needed for the formation of muscles, bones, blood cells, enzymes, hormones, tendons, hooves, skin, the internal organs such as heart and liver, and indeed almost all body tissues. Proteins are made from chains of building blocks, called amino acids. There are 22 amino acids recognised as important in the horse's diet. Approximately 12 of these amino acids are known as 'essential amino acids' as they have to be provided in the diet. The other amino acids can be synthesised by the horse as long as adequate protein is provided. Two of the essential amino acids most commonly in short supply or limiting to performance are lysine and methionine.

Cereals and soya

HIGH PROTEIN Feedstuffs in the diet include:	% Protein		gms/kg protein
Peas:	23%		(230g/kg)
Soya Beans:	44-48%		(440-480g/kg)
Alfalfa Hay or Alfalfa Chaff:	15-23%		(150-230g/kg)
Linseed:	32%		(320g/kg)

LOW PROTEIN Feedstuffs in the diet include:
Seed Hay:	4-8%		(40-80g/kg)
Meadow Hay:	6-12%		(60-120g/kg)
Maize:	8%		(80g/kg)
Wheat/Barley/Oats:	10-12%		(100-120g/kg)
Bran:	13-15%		(130-150g/kg)
All cereals are particulary low in essential amino acids.

PASTURE has a very variable protein content depending upon the season. Typical levels are as follows:
Spring	30%+		(300 g/kg DM)
Summer	10-14%		(100-140 g/kg DM)
Autumn	14-20%		(140-200 g/kg DM)
Winter	10%		(100 g/kg DM)

Energy and Fibre
Energy is needed for maintenance of health and normal body functioning, eg breathing, temperature control etc. Additional energy over and above these MAINTENANCE requirements are needed for PRODUCTION which may take the form of growth, lactation or athletic performance. Energy can be derived from several sources in the diet:

1. 'Simple' Carbohydrates (sugars and starch)

Maize

Oats

Coarse Mix

Extruded Barley

'Simple' Carbohydrates (sugars and starch) derived from cereals, molasses and of course there are very high levels of simple carbohydrates in Spring grass, and again in the Autumn flush of pasture.

The following are typical sugar levels in common horse feeds: Typical Sugar Level on DM Basis g/kg
Cubes:	12.5 - 25 g/kg
Mixes:	37.5 - 50 g/kg
Molassed Chaff:	225 - 250 g/kg
Alfalfa Chaff:	85 - 100 g/kg
Sugar Beet Pulp:	Up to 28% (280g/kg)
Spring Grass:	Up to 250g/kg
Molasses:	39 - 49%

Thus the horse in the wild would receive quite a high sugar intake for some months in the year and a reduced level during the rest of the year, so he does receive 'sugar' in his 'natural' diet. Simple carbohydrates should be digested by chemicals (enzymes) primarily in the small intestine but in cases of overload, such as access to an abundance of Spring grass, the small intestine becomes overwhelmed, and the sugars and starch pass undigested into the hindgut. The microbial fermentation of these simple carbohydrates can lead to many disorders ranging from laminitis to rhabdomyolysis (tying up). Simple CHOs are broken down to form predominantly glucose, which is transported via the bloodstream from the gut to the muscle and other body cells to act as an energy source at a cellular level. The simple CHOs not immediately required as an energy source are converted to a compound called glycogen and primarily stored in the muscles and liver for future use. If there is a significant over-supply of energy it will be stored as adipose tissue (body fat). The major forage sources fed to the modern horse include pasture, hay, wilted bagged forages and straw. Other feedstuffs providing high levels of complex CHOs include Sugar Beet and Chaff.

2. Complex Carbohydrates
These are often collectively known as fibre sources or forage and include cellulose, hemicellulose, lignin and other compounds. Fibre may be:

INDIGESTIBLE (often referred to as roughage) and is an important dietary component, as it helps maintain gut motility and provide 'scratch factor' and the feeling of satiation, or:

DIGESTIBLE from which the horse can derive nutrients.
Indigestible fibre or roughage is the woody or lignified fraction of the plant which is not affected by the microbial fermentation and passes undigested through the gut. It plays an important role in keeping the gut contents moving.

Digestible Fibre comprises those complex CHOs which cannot be digested enzymetically but which can only be broken down by the millions of beneficial micro-organisms (bacteria, yeasts, protozoa) which colonise the hindgut of the horse. These complex CHOs are broken down to produce compounds called volatile fatty acids (VFA's) which are utilised by body cells to produce energy. The energy produced from the fermentation of digestible fibre should be sufficient to meet energy requirements for maintenance and light work as long as the forage is of high quality and has a suitable ratio of digestible to indigestible fibre.

Horses have evolved as fibre eaters and their digestive system is designed to process large amounts of relatively poor quality fibre. However, the demands made upon modern horses mean that they would not be able to meet these demands on poor quality fibre sources alone. Using higher quality forage with a greater proportion of digestible fibre is necessary to help meet the nutrient requirements of the modern horse.

As a general rule the more mature the plant, the greater the proportion of stalk to leaf, and the more indigestible the overall plant becomes. All plant material contains fibre, but the seeds, eg cereals, provide much lower levels of fibre than the stalk and leaves.

Most horses require at least 50% by weight of their diet to comprise complex CH0 fibre sources (hay, wilted bagged forage, pasture) or if long fibre is in short supply chaff can replace a proportion of the long fibre. Many horses and ponies in light work can derive most of their nutrient requirements from long fibre and indeed pasture can contain high sugar levels and very digestible fibre, in the Spring and Autumn, and it often exceeds the horse and pony's requirements leading to overload disorders such as laminitis.

3. Oils and Fats
These are made up from chains of fatty acids. As with the amino acids some of the fatty acids are more important than others. Soya oil, corn oil, wheatgerm oil and cod liver oil are all good sources of essential fatty acids. Oils and Fats provide more than twice the energy of CHOs and may be added to the diet of performance horses up to 8% of the horse's total ration. (As with all feedstuffs oil should be introduced gradually. High dietary oil levels should only be used under expert advice as the requirements for other nutrients may be affected by high oil levels).

4. Minerals and Vitamins
Almost every body process depends for correct functioning on the adequate presence of various minerals and vitamins. Minerals and vitamins rarely act in isolation but interact extensively with each other and with other nutrients. Thus a deficiency imbalance or excess of one mineral or vitamin can affect many body processes. In the wild the horse fulfilled his mineral and vitamin requirements through selective grazing of herbage from various types of soil encountered whilst he wandered over many thousand of miles. The modern horse, even when grass kept, does not have access to this density of plants or soils, and thus must rely upon concentrate feeding to complement and supplement the minerals and vitamins naturally present in the pasture or preserved forage.

MACROMINERALS (required in larger amounts in the diet)
Macromineral		Specific areas of involvement		Signs of deficiency or excess
Calcium and phosphorous		Bone and tooth growth and development. Blood formation and clotting. Muscle contraction. Nervous system activity. Lactation.		Rickets and other bony disorders. Kidney disorders. Poor muscle function. Inadequate nervous transmission. Impaired digestion. Impaired blood clotting. Major interactions - vitamin D, Magnesium.
Magnesium		Bone and tooth growth and development. Enzyme activation		Bone and tooth growth and development. Enzyme activation Nervousness. Muscle tremors. Sweating. Bone disorder. Heavy breathing. Major interactions - calcium, phosphorous, vitamin D.
Potassium, sodium, chlorine		Body fluid retention. Nervous transmission. Muscle metabolism. Blood formation.		Reduced growth rate. Reduced appetite (anorexia). Sweating. Muscle tremors. Tetany. Impaired nervous transmission. Kidney failure.
Sulphur		Amino acid formation. Hoof and horn growth. Enzyme and hormone production.		Poor horn and hair growth, impaired protein metabolism. Impaired muscle metabolism.

MICROMINERALS OR TRACE ELEMENTS (required in very small or trace amounts in the diet)
Macrominerals		Specific areas of involvement		Signs of deficiency or excess
Copper		Haemoglobin formation bone development - maturation enzyme activation muscle function.		Bone disorder. Impaired pigmentation. Dry, brittle coat. Muscle problems.
Zinc		Enzyme activation. Skin and hair formation. Blood formation. Bone development. Lactation.		Reduced growth. Poor bone growth. Hair loss and skin disorders. Bone disorders.
Manganese		Enzyme activation. Skin and hair formation. Blood formation. Bone development. Lactation.		Reduced growth. Poor bone growth. Hair loss and skin disorders. Bone disorders.
Iron		Haemoglobin formation. Enzyme activation for many body processes.		Reduced growth. Anaemia. Poor performance. Scouring.
Selenium		Maintenance of muscle cell membrane integrity and other antioxidant properties.		Muscle disorders (including white muscle disease in foals, azoturia, tying up) Hoof sloughing
Iodine		Thyroid gland formation		Goitre. Possible effects on fertility
Cobalt		Vitamin B12 synthesis		Poor appetite. Liver dysfunction (see vitamin B12)
Chromium		Insulin activity component of glucose balance factor. Immune system. Stress.		Not yet known in the horse - muscle dysfunction and poor immune system function

Vitamins
These may be divided into two groups:

1. Fat soluble vitamins (which can be stored in the body fat and therefore retained for some time) include vitamins A, D, E and K.
   
2. Water soluble vitamins, of which the horse requires a daily supply, include vitamin C and the B complex vitamins. Some vitamins from both groups can be manufactured by the horse. For example, B complex and K can be synthesised by the microbrial population in the hind gut, providing certain conditions of diet and environment are met. Furthermore, vitamin D can be manufactured by the action of sunlight on sterols present in the skin, and vitamin C by the liver. Almost every body process requires the presence of one or more vitamins for correct functioning. They may act in isolation, in combination with other vitamins, or interact with minerals. Vitamin activity is sensitive to light, heat, moulds and oxidising agents and will deteriorate with time, especially if exposed to these conditions. Thus, feed storage should be closely controlled.

FAT SOLUBLE VITAMINS
Fat-soluble vitamin		Specific areas of involvement		Signs of deficiency or excess
Vitamin A (may be referred to as beta-carotene, a precursor of vitamin A which is converted by specialist cells in the gut to the active form retinol).		Normal eye function. Maintenance of tissue integrity, especially reproductive, urinary and nervous systems. Correct functioning of the immune system. May be stored in the liver and fatty tissues.		Anorexia (poor appetite). Reduced growth. Night blindness. Continuous tear production. Keratinisation of the eye. Poor hoof and coat condition. Infertility. Respiratory and nervous disorders. Salivary gland abscesses.
Vitamin D (if the horse is on good grazing with adequate daily exposure to sunshine he is able to manufacture sufficient levels of vitamin D to meet normal maintenance requirements. Stabled, grass kept and hard worked horses may require a daily dietary supply, especially during the winter months).		Bone structure. Joint and cartilage integrity. Absorption of calcium and phosphorus from the gut.		Bone disorders. Swollen joints. General unthriftiness and weight loss. Muscular and nervous dysfunction. Calcification of soft tissue (lungs, heart etc). Major interactions - calcium, phosphorus, magnesium.
Vitamin E (may be referred to as alpha tocopherol)		Maintenance of muscle and other body cell integrity. Antioxidant properties. Reproductive efficiency. Integrity of the nervous system. Sperm production and quality.		Muscular disorders. Infertility. Nervous disorders. Major interaction - selenium.
Vitamin K (daily maintenance requirements may be met through gut microbial synthesis if good quality forage is available. A dietary source will be required if the microbial population is disrupted through the use of intensive antibiotics, rapid diet changes or immaturity of the foal's gut).		Blood clotting mechanism.		Clinical deficiency is very rare but a subclinical deficiency may predispose to pulmonary bleeding and internal haemorrhage.

Water Soluble Vitamins
In the normal, healthy horse, provided with ample high quality green fodder or conserved forage, the daily maintenance requirements for water soluble B vitamins will be manufactured by the gut microbes. However, horses in work may require additional dietary supplementation. Disruption of the microbial population, arising from rapid dietary changes or antibiotic therapy, may lead to a deficiency of any or all of the water soluble B vitamins. A dietary supply will then be necessary.

WATER-SOLUBLE VITAMINS
Water-soluble vitamin		Specific areas of involvement		Signs of deficiency or excess
Vitamin C Ascorbic acid		Bone and teeth structure. Gum health. Blood vessel integrity. Reproductive efficiency.		Swollen gums. Internal bleeding. Anaemia. Major interactions - copper and iron.
Vitamin B1 Thiamine		Carbohydrate, protein and fat metabolism. Correct functioning of the nervous system.		Anorexia and weight loss. Limb inco-ordination. Increases blood pyruvate Hypertrophied heart. Major interactions - all other B complex vitamins. Deficiency symptoms can be caused by ingestion of plants such as bracken, mares tail and yellow star thistle which contain thiaminase.
Vitamin B2 Riboflavin		Carbohydrate protein and fat metabolism. Nutrient utilisation. Energy release.		Poor growth rate. Poor use of feedstuffs. Possible involvement in eye dysfunctions. Major interactions - all other B complex vitamins.
Vitamin B6 Pyridoxine		Carbohydrate metabolism. Enzyme activation. Protein and fat digestion.		Poor digestion. Inhibition of amino acid production. Major interactions - all other B complex vitamins.
Vitamin B12 Cyanocobalamin (adequate cobalt must be present for bacterial B12 synthesis)		Carbohydrate protein and fat utilisation. Liver function. Muscle metabolism.		General unthriftiness and poor feed utilisation. Major interactions - copper, all other B complex vitamins, choline.
Niacin (Nicotinic acid)		Enzyme systems. Cell integrity and metabolism.		Poor growth and development. Poor appetite. Poor coat condition and hair loss. Diarrhoea. Major interactions - all other B complex vitamins.
Pantothenic acid (usually present as calcium pantothenate)		Enzyme systems. Protein, carbohydrate and fat digestion. Correct functioning of the nervous system.		No specific signs recorded for the horse but other species suffer from: poor growth, reproductive failure, skin lesions, digestive dysfunction, hind limb abnormalities.
Folic acid (Folacin)		Health and maturation of red blood cells. Growth and development.		Anaemia due to decreased number of functional red blood cells. Poor performance. General debility. Major interactions - other B complex vitamins.
Biotin		Hoof formation. Fat metabolism.		Shelly feet - cracking of the wall from the ground surface. (Specific symptoms may be masked by symptoms of a general B complex deficiency). Major interactions - vitamin C and B complex, methionine, choline.
Choline		Fat metabolism, especially fat removal from the liver.		Fatty liver (suspected in the horse). Poor growth. Inco-ordination. Major interactions - vitamin B12, methionine.

Other vitamins and other, as yet, 'unidentified growth factors' may be required for growth, development and performance. Until these are known and their roles determined it is essential that a consistent, balanced ration is fed to all types of horse and pony.

5. Water
Water is an essential nutrient involved in almost all metabolic reactions. The body tissues of a mature horse contain about 60% water, whilst those of a young horse contain 70-80% water indicating the extra requirement for water during growth. The horse can lose almost all its body fat or over half its body protein without major ill effects, but a 10% water loss can cause disorders and a 20% loss can be fatal. The average horse requires approximately 12 gallons of water per day depending on workload, dietary constituents, relative humidity and stage of life-cycle. Water quality is also important. Level of nitrates, heavy metal contamination and degree of microbial contamination may all affect the horse.