Minerals

Calcium and phosphorus are the chief elements of the skeleton; 99% of the calcium and about 80% of the phosphorus found in the body are located in the bones and teeth. The nutritional role of calcium is closely related to that of phosphorus, and we shall therefore consider the two elements together.

Calcium ions are principally absorbed in the proximal (upper and middle) part of the small intestine, and their absorption can be enhanced by ensuring an adequate supply of vitamin D in the diet at the same time. The excretion of calcium takes place via the large intestine and the kidneys, and the amount excreted fluctuates strongly. The dietary calcium in growing animals, for example, may be very high but the proportion of calium excreted extremely low as the calcium absorbed is needed for the skeletal development.

Phosphorus is absorbed mainly in the lower part of the small intestine. As in the case of calcium, it is difficult to assess the actual amount absorbed because it can be affected by a number of factors. It has been proved, however, that the intake of vitamin D and the correct ratio of calcium to phosphorus both improve its absorption.

Calcium’s main function consists of forming bones and teeth and, in the case of birds, the additional calcium needed for egg shell formation. Calcium is also present in soft tissues where it carries out a number of regulatory functions in the body such as stimulating muscle contractions, making it important to the work of the heart. The greatest concentration of calcium not in the bones and teeth is found in the blood. All of the larger animals have 10mg of calcium per 100ml of serum. The vital minimum level of calcium in the serum is not regulated by the amount of calcium ingested, but is mobilised from the bones, which act as a calcium reserve.

In addition to the role of phosphorus in bone formation, it also plays a primary part in the carbohydrate metabolism, is active in fat metabolism and other life processes, and is the very core of the energy transmission system of the metabolic machine.

Because of the close relationship between the calcium and phosphate metabolisms, the ratio of calcium to phosphorus in the diet is of extreme importance, particularly for normal calcification of the bone and for reproduction. For most species of mammals the satisfactory range lies between 1.2 – 1.5:1, but the supreme calcium-to-phosphorus ratio for birds is regarded as 1.6 – 2:1.

Osteomalacia, rickets and a high incidence of bone fractures can all be the result of a calcium deficiency, which can also lead to heart and circulatory troubles. A deficiency of phosphorus in the diet can produce diarrhoea and loss of weight even when the daily food intake itself is high. Another deficiency symptom is reduced fertility.

About 60% of the body’s magnesium is found in the skeleton. The remaining 40% is scattered throughout the body fluids. Magnesium activates many enzyme systems, particularly those concerned with the carbohydrate metabolism.

A normal blood count depends on magnesium to a great extent, for 100ml blood serum contains 1 – 3mg of magnesium. Diets extremely low in magnesium will cause hyperirritability, tetany, muscle twitching and reduced blood pressure.

Magnesium is absorbed from the small intestine and is excreted in both the faeces and Urine.

All three elements are closely related metabolically and they all serve a vital function in regulating and balancing certain processes in the organism.

Potassium and sodium are absorbed primarily from the small intestine, but apparently some absorption of the latter also takes place from the stomach. Chlorine is absorbed chiefly from the small intestine. All three elements are mainly excreted via the kidneys.

The main functions of the sodium ion in the animal body appear to be connected with the regulation of osmotic pressure (the pressure against a membrane between a concentrated and a less concentrated liquid) and the maintenance of acid-base balance, although together with potassium and chlorine it plays an important role in water metabolism as well. Potassium also regulates the osmotic pressures and the acid-base balance but from within the cells, whereas sodium carries out these functions in the extracellular fluids of the body.

Close relationship exists between chlorine and sodium, too, both of which are found in the extracellular fluids, and therefore both are responsible for the regulation of the osmotic pressure outside the cell. Chlorine constitutes about two-thirds of the total anions of blood plasma.

The interrelationship between these three elements becomes clear when we see that excess chloride retards growth if it is not compensated by sodium and potassium, and vice versa.

A sodium deficiency will adversely affect appetite and normal increase in weight and cause low blood pressure, rough coat and cardiac troubles.

The abundance of potassium in both plant and animal foods normally precludes the danger of a deficiency in this element. In fact, the healthy balance between sodium and potassium in the body is often upset by excess potassium, which can only be regulated by an increased intake of water and sodium.

A chloride deficiency can retard growth as well as adversely affect viscosity and nerve Impulses.

The sulphur of the body occurs almost entirely in organic compounds, notably in proteins where it is a component of the sulphur-containing amino acids such as cystine and methionine. Except in the case of ruminants, inorganic sulphur is ineffective in satisfying body requirements.

Because of their terrible taste and because they act as a laxative, e.g., Glauber’s salt or Epsom salt, animals are not partial to the fast soluble sulphates, sodium or magnesium sulphate. That is why the sulphur in today’s diets or supplements is in the form of the sulphur-containing amino acids cysteine, cystine and methionine.

In spite of the fact that there are as much as 60 – 90mg iron per kilo body weight in the animal body it still counts as a trace element. Seventy percent of iron is found in haemoglobin – the colouring matter of red blood corpuscles – the remaining 30% is found chiefly in the liver, to some extent in the spleen and bone marrow, and in plasma.

The absorption of iron is influenced by the state of the body’s iron stores. Dietary iron is ionised by the stomach acids then passes into the cells of the intestinal lining, and the rate at which it is released from these cells into general circulation depends on how saturated with iron the blood protein transferrin is. The body’s need for iron thus affects the absorption of the element from the gastrointestinal tract.

Absorbed iron is converted into haemoglobin and is therefore part of the process where oxygen is taken up from the air in the lungs and carried to the tissues. It contributes to the energy metabolism and aids resistance to infection. Anaemia is the well-known result of an iron deficiency, but a lack of this trace element can also lead to an increased susceptibility to infection and symptoms of toxicosis.

Like iron, copper is stored in the liver but is also found to a lesser extent in bone marrow. The animal body contains 1.5 – 2.5mg per kilo body weight.

Copper and iron are sometimes considered together because of their joint importance in the formation of haemoglobin. Because of this relationship, anaemia can result from a copper deficiency as well as from an iron deficiency. A deficiency of copper decreases fertility in cattle and hatchability is reduced in birds. Embryonic abnormalities can occur in birds on a diet poor in copper.

Copper has an important function in hair growth, the formation of the melanin (dark) pigment of skin and hair, and the bone and connective tissue Formation.

The small amounts of manganese in the animal body – approx. 0.2 – 0.3mg per kilo body weight – are concentrated mainly in the bone. Manganese is essential for bone growth, fertility and to prevent perosis (slipped tendon) in poultry. It also supports the amino acid metabolism.

Due to poor absorption of manganese in the gastrointestinal tract and the low concentration of this trace element in the body tissues, great care must be taken to ensure a regular supply of manganese in the diet. A deficiency of this element frequently affects skeletal development, particularly in birds, and results in shortened and often deformed limbs. A low manganese diet can often lead to sterility in male mammals and late sexual maturity in females. As already mentioned, perosis in birds is the result of a lack of manganese in the food ration and should a choline, vitamin E and biotin deficiency arise at the same time an outbreak of this syndrome is unavoidable.

The animal body contains abut 20 – 30mg zinc per kilo body weight, and most of it is found in the liver, kidneys, bones, hair and pancreas. The main site of zinc absorption is the duodenum. An excess of calcium inhibits zinc absorption, meaning an increased intake of zinc is necessary if the dietary share of calcium is high. The amount of zinc in the diet should be increased, too, when corn or soy bean meal form the staple food.

Zinc is important primarily for skeletal development and the formation and regeneration of the skin and hair cells. Symptoms of a deficiency, particularly in young animals, are bone deformation and retarded growth as well as impaired hatchability and poor feathering in birds.

Cobalt is of significance primarily in ruminant nutrition, and it is generally here that a deficiency produces symptoms of disease or illness. Cobalt is an integral part of vitamin B12 and is used in the synthesis of this vitamin by the rumen microflora. A deficiency of vitamin B12 is therefore responsible for the metabolic failure found in cobalt deficiency in ruminants. This means that more attention should be paid to ensuring a sufficient supply of vitamin B12 rather than cobalt in the diet. In view of the expense, however, a direct cobalt supplement would be more applicable in the case of ruminants.

About 80% of the iodine contained in the animal body is to be found in the thyroid gland. Iodine’s chief role is as a component of thyroxin, which frees the hormones in the gland, regulating the metabolic rate of all bodily processes. Iodine is absorbed as iodide primarily in the small intestine, although a small quantity is already taken up by the stomach.

A dietary insufficiency of iodine means an absence of sufficient thyroxin in the blood causing the thyroid to work harder to produce thyroxin and, in the process, enlarging it to what is called goitre. Goitre even occurs in the newborn, primarily as a result of insufficient iodine in the diet of the pregnant female. The thyroid hormone is essential for normal growth and reproduction in all mammals and birds, so that a deficiency leads to a depressed basal metabolic rate, disturbed propagation and stillborn babies.

Selenium is one of the essential nutrients in the living organism. The role of selenium is to participate in the functioning of the enzyme glutathione peroxidase (GPx). It is responsible in the body for the degradation of various metabolic intermediates and thus essential for many metabolic processes. In addition, selenium is also known for its role in the immune system. It supports the formation of antibodies and important messengers. Selenium deficiency can lead to increased susceptibility to disease due to immunosuppression. Due to the significant selenium deficiency in our soils, the plants can not absorb enough selenium, which in turn often leads to selenium deficiency in the animal feed plants. Therefore, selenium should be supplemented, albeit in very small amounts. In overdose, selenium is toxic.

Like selenium fluorine occurs in practically all foods and feeds and is to be found in all forms of nature, so that it is normally not necessary to add it to the diet. In addition, an overdose over a period of time eventually interferes with growth, lactation and reproduction. Fluorine plays a role in strengthening the bones and teeth and promoting normal growth in certain species.

In general an animal kept under normal conditions and given one of the standard commercial diets rarely suffers from a deficiency of these trace minerals. It was only through feeding animals on diets purified of these microelements that they were found to be essential at all. It is not necessary to discuss these trace elements in detail here, therefore, as adequate amounts of each are to be found in pet food today.

All these elements are essential in one way or another. Vanadium and chromium improve the growth rate of rats; silicon appears to be necessary for normal growth and skeletal development of chicks, tin likewise, and a nickel deficiency results in an inferior liver function. Practically all of them, however, have been shown to be toxic in comparatively slight overdoses.