Some vitamins and minerals work together, some will interfere with the absorption of others. Therefore if a horse is receiving too much of one it may cause an artificial deficiency in the other by limiting the ability of the horse to utilise it. Eg: high levels of phosphorus can lead to a calcium deficiency because the phosphorous 'holds on to' the calcium and the horse's body cannot use it!
There are 15 vitamins which are essential to the horse but requirements will vary from horse to horse - they are all individuals!
There are 2 types of vitamins; those that are fat soluble and can be stored by the body ie: vitamins A, D, E & K and those that are water soluble and cannot be stored such as: the B vitamins and vitamin C.
Fat soluble vitamins are generally found in green herbage eg: grass and so horse's with access to grass during the summer will take in more than they need and store the excess for the winter. However, the soil type and soil quality will affect the vitamin content.
- Vitamin A (Retinol): is converted from carotene within the walls of the intestines. It is necessary for vision, health of mucous membranes, growth, reproduction and resistance to disease. It is found in green forages, carrots and apples. Deficiency in vitamin A will lead to reduced sight and eye damage which can result in night blindness. Other signs are poor and uneven hoof growth, reproductive failure and the susceptibility to disease. Excessive vitamin A can lead to fragile bones and skin damage.
- Vitamin D (Calciferol): is needed for the absorption, uptake and transport of calcium and phosphorus. It occurs when 2 pro-vitamins are converted to vitamin D when ultraviolet light acts on the skin. These pro-vitamins are found in most forages. Deficiency in vitamin D leads to swollen joints, skeletal abnormalities and lameness. Excessive vitamin D can cause bone to be laid down in soft tissue. Horses need sunlight!
- Vitamin E (Tocopherol): is important for the reproductive system and is important for muscle tissue and red blood cells. It works with Selenium. Deficiency will lead to pale areas of skeletal and heart muscle, fragile red blood cells and infertility. Vitamin E is found in grain, seeds and green herbage eg: alfalfa.
- Vitamin K: is needed for effective blood clotting. This vitamin is made by the gut bacteria so deficiency is rare and is also found in leafy plants.
Water soluble vitamins are mostly synthesised by the bacteria which are found in the horse's gut.
- Vitamin B1 (Thiamine): is essential for many enzyme systems particularly those that regulate energy release from stored carbohydrates and fat - as mentioned in last week's blog. Found in yeast, alfalfa, leafy green crops such as peas, beans and cereal germ. It is also synthesised in the gut as mentioned earlier - but this can be affected by anti-biotics. Deficiency is therefore rare but will show as lack of energy, muscle weakness and cramp. If there is a slight deficiency a horse may eat less food and so drop condition.
- Vitamin B2 (Riboflavin): is a fundamental component of many enzymes which are involved in protein and carbohydrate metabolism. It cannot be synthesised by the horse but is found in green forage, so good quality grass and hay should provide plenty. A deficiency will lead to decreased energy production and growth and condition will be effected. Moon blindness can result from severe deficiency and this will lead to conjunctivitis.
- Vitamin B3 (Niacin): is important in the metabolism of carbohydrates, fats and protein. It can be found widely in feeds including lucerne. Signs of a deficiency include skin disorders, or disorders of the gut and nervous system eg: ulcers of the mouth, scaly skin and nervous system upset.
- Vitamin B5 (Pantothenic Acid): is involved in the metabolism of fatty acids and the formation of antibodies - which are an important part of the immune system. It is also synthesised in the gut but can be found in peas, molasses, yeast and cereal grain. Deficiency is rare but signs are weight loss, growth failure, dermatitis and skin disorders.
- Vitamin B6 (Pyridoxine): is important to the enzyme systems which are involved in protein and carbohydrate metabolism. This vitamin is also involved in producing haemoglobin, preventing disease and nervous system activity. Found in forages, grains and pulses the wide range of activities vitamin B6 is involved with means that deficiency signs are non-specific.
- Vitamin B12 (Cyanocobalamin): is needed for the production of red blood cells and is synthesised only by the bacteria in the horse's gut. Although it can be found in fish and meat and bone meal. Deficiency is more often seen in youngsters and signs include a loss of appetite, poor growth rates and anaemia.
- Folic Acid: is linked to vitamin B12 and is vital for red blood cell production. Found in pasture, hay and cereals and is also synthesised in the gut. A deficiency is shown by anaemia and poor growth.
- Biotin: is involved in fat, protein and carbohydrate metabolism. Found in maize, yeast and grass as an available source. Deficiency results in poor hoof growth and changes in the skin.
- Choline: is essential for building and maintaining cell structure and is important for fat metabolism and nerve transmission. Found in green leafy forages, yeast and cereals a deficiency will lead to slow growth and an increase in fat deposited in the liver.
- Vitamin C (Ascorbic Acid) : is important for normal collagen formation, maintenance and repair. Collagen is vital to skin structure and connective tissue. Also, important in transferring iron from blood to storage in the body. Found in green leafy forage and synthesised by the horse deficiency is rare. In humans a deficiency is seen as delayed wound healing, oedema and weight loss.
It is useful to understand a bit about vitamins and what they do to help understand more about food and feeding! Look out for next week's blog about minerals.
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