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THE VITAMINS
The vitamins are classified as fat-soluble and water-soluble. The fat-soluble group includes vitamins A, D, E and K and the water-soluble group – vitamin C and the numerous members of the vitamin B complex.
Vitamin A is a colourless substance of known chemical constitution which is found in the liver oils of fish and animals. It is formed in the animal body from pigments called carotenoids associated in the plant with the green colouring material chlorophyll. Carotene is not very stable and is quickly destroyed in the presence of oxygen. Dried grass of high quality is the best source of the vitamin. Vitamin A deficiency in young cattle is not uncommon. The main signs are failure to thrive, night blindness and, later, total blindness due to damage of the optic nerves. In all animals secondary bacterial infections occur where the deficiency is prolonged, and it may lead to the death of an animal.
Vitamin D was first identified as a substance, present in cod-liver oil, which was essential to the prevention of rickets. Vitamin D, in fact, is often called the anti-rachitic factor. Rickets, the disease due to vitamin D deficiency, is characterized by a failure of the animal to lay down calcium and phosphorus in its bones. Rickets can occur as a result of a deficiency of calcium or phosphorus in the diet.
Vitamin E is a dietary ingredient essential for the reproduction of rats.
Vitamin C is required only by guinea-pigs, humans, and the higher apes, where a lack causes scurvy. Farm animals and birds manufacture the vitamin in their systems.
Vitamin B complex. The remaining water-soluble vitamins are all grouped under this one name. No member of the vitamin B complex is required by adult ruminants, the reason being that the microorganisms of rumen, besides transforming food proteins and breaking down the fibrous constituents of feeds, manufacture the vitamins of B complex in sufficient amounts to meet the needs of their host. Before the rumen of the young animal is fully established it needs a source of these B complex vitamins in its ration, but once the rumen flora is established the need comes to an end. Recent experiments have shown that horses do require some member of the vitamin B complex, but it does not appear likely that practical rations would ever be deficient. Hence pigs and poultry, and the farm dog, are the only farm animals which are ever likely to suffer from major deficiencies.
Дайте відповіді на запитання.
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1. How are the vitamins classified?
2. What vitamins does the fat-soluble group include?
3. What substances does the water-soluble group include?
4. What is vitamin A like? Where is it found?
5. What are the main signs of vitamin A deficiency?
6. How was vitamin D first identified? Where is it found?
7. What is rickets characterized by?
8. What is vitamin E?
9. Do farm animals and birds require vitamin C and vitamin B complexes?
Вправи
I. Згрупуйте подані нижче слова за частинами мови.
| Іменник | Прикметник | Дієслово |
| vitamin | soluble | classify |
includes, numerous, complex, colourless, chemical, liver, is destroyed, stable, uncommon, failure, thrive, lead, was identified, is called, anti-rachitic, is characterized, deficiency, lay down, dietary, scurvy, is required, fibrous, appear, sufficient, suffer, deficient.
II. Прочитайте слова та здогадайтесь про їх значення.
calcium, phosphorus, ingredient, reproduction, complex, ration, flora, experiment.
III . Знайдіть спільне слово.
a)disease, rickets, brucellosis, tuberculosis
b)vitamin A, substance, water, carotene, oxygen
c)pigments, carotenoids, chlorophyll.
IV. Згрупуйте подані нижче слова у синонімічні пари.
oxygen, gas, thrive, grow, ingredient, constituent, manufacture, produce, rumen, stomach, substance, material, sufficient, enough, deficiency, lack.
V. Заповніть пропуски у реченнях, використовуючи слова в дужках.
1. The water-soluble group … vitamin C and the numerous members of the vitamin B complex.
2. Vitamin A … in the liver oils of fish and animals.
3. Vitamin A … in the animal body from pigments called carotenoids.
4. Carotene … in the presence of oxygen.
5. Secondary bacterial infections … in all animals, where the deficiency of vitamin A … .
6. Vitamin C … only by guinea-pigs, humans, and the higher apes.
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7. Farm animals and birds … the vitamin in their systems.
8. Before the rumen of a young animal … it needs a source of B complex vitamins.
9. Pigs, poultry and farm dogs … to suffer from major deficiencies.
(is prolonged, manufacture, is found, is formed, are likely, is destroyed, includes, occur, is required, is established).
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