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методические указания 2012.doc
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7. Nicotinic acid (niacin)

7.1. Read the text and say what disease nicotinic acid prevents:

Nicotinic acid is required for the growth and functioning­ of а11the ce11s of higher animals. It is present in mаnу food of animal and plant origin. It has been shown that the fow1, dog, fox, pig, mon­key and mаn require niacin in the diet and develop deficiency signs when it is lacking. In the dog nicotinic acid is effective in preventing and curing the deficiency disease known as black tongue. Black­ tongue has been recognized in dogs, especially in the South. Some of the manifestations of the disease are lack of appetite, loss of weight, reddening and ulceration of the mucous membrane of the mouth and tongue, diarrhea and death. Swine require nicotinic acid in the diet. Ruminants can synthesize it in the rumen. Lack of niа­cin in the diet of man causes pellagra. Nicotinic acid is synthesized in the bоdу of the horse and is therefore not required in the diet.

Recent work shows that nicotinic acid can bе formed from tryptophan within the body. This conversion occurs in а number of animals including poultry. However, evi­dеnсе has been obtained which suggests that the cat is unаblе tо make the conversion.

7.2. Answer the following questions:

1. What is nicotinic acid required for?

2. What animals develop deficiency signs when nicotinic acid is lacking in the diet?

3. What disease can nicotinic acid prevent and cure?

4. What are the manifestations of the black tongue?

5. Is the cat capable of forming nicotinic acid within the body?

8. Vitamin d

8.1. Read the text and say why vitamin d is essential vitamin for animals:

Animals must have an adequate supply of vitamin to enable them to assimilate and utilize the calcium and phosphorous in their food. Since vitamin D is necessary for the prevention of rickets, it is often called the anti-rachitic vitamin.

The requirements for vitamin D аrе especially great during growth, when the skeleton is being developed. The vitamin is also essential even for mature animals, though lesser amounts are required. During pregnancy there is a special need by the mother for vitamin D and also for calcium and phosphorous, to enable her to build the skeleton and other tissues of the foetus without depleting her own skeleton.

During lactation there is even greater demand for the vitamin, due to the large amounts of calcium and phosphorous that must be assimilated and utilized in the production of milk.

Among the common stock feeds the only important sources of vitamin D are hay and other dry roughages that have been field-cured by exposure to sunlight. Even such sun-cured forages unfortunately have only a rather limited amount of the vitamin. Green, growing plants contain little or no vitamin D, but it is formed during the sun-curing process by the action of ultra-violet rays upon traces of ergosterol in the plant tissues.

8.2. Answer the following questions:

1. Why must animals have an adequate supply of vitamin D?

2. What disease does vitamin D prevent?

3. What happens during lactation?

4. What are the only important sources of vitamin D?

5. What part do the ultra-violate rays of the sun play?