標題: 英文原文 [打印本頁] 作者: wanzheng98 時間: 2009-2-27 11:41 標題: 英文原文 大家誰有專業方面的英文原文，發上來點吧？非常感謝作者: yuxianren 時間: 2009-2-28 08:26
要那方面的
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Other Roots and Succulents
Root crops were at one time grown quite extensively in North America and Eu¬rope as sources of winter feed for livestock. Because of high labor costs for pro¬ducing them and lower yields of nutrients compared to hybrid corn and other crops, there is very little production of root crops in the United States, although they are still important in northern Europe. Some of the more important root crops include mangels (Beta vulgaris), turnips (Brassica compestris var. rapd), rutabagas or swedes (Brassica rapus var. napobrassica), and field carrots. Mangels are similar to sugar beets except that they are longer, higher yielding, and have a lower sugar content. Approximately 40 percent of the total length of the root ex¬tends above the soil surface. After harvest, root crops are stored in cellars or out¬door pits, and protected from freezing. They can also be used as green feed and harvested directly by grazing stock. Because most of the carbohydrate in fodder beets exists as sugars rather than as starch, the beets are very rapidly fermented in the rumen (Sabri et al., 1988a), and there is a potential for acidosis to occur. Their digestibility in ruminants is very high, with the digestibilities of dry matter and gross energy near 96 percent in sheep (Sabri et al., 1988b).
Sweet Potatoes and Yams Sweet potatoes {Ipomoea batatas) are grown primarily for human consumption. A member of the morning-glory family, the sweet potato grows in warm climates with long growing seasons, primarily in trop¬ical and subtropical areas. Cull sweet potatoes are used as animal feed. The tubers contain trypsin inhibitors, and so must be cooked before using as feed (Bouwkamp, 1985). They are similar to potatoes in feeding value. Sweet potato chips have about 79 percent of the metabolizable energy content of corn for swine (Wu, 1980) and can replace corn in swine finisher diets (Tor-Agbidye et al., 1990). Dried sweet potato meal can replace up to 40 percent corn in broiler diets with no adverse effects on performance (Ravindran and Sivakanesan, 1996). In Asia, it is common to feed the sweet potato vines, which are very palatable, as well as roots, to pigs. The vines are also used as forage for ruminants. If they become moldy, both the roots and vines can be toxic, producing lung disease (pulmonary emphysema). This is caused by 3-substituted furans (e.g., ipomeanol) produced as stress metabolites in response to fungal infection.
Yams {Dioswrea spp.) are similar to sweet potatoes in appearance and nu¬trient content. They are used primarily for human consumption. Grown mainly in the tropics, yams can be used as feed for pigs or other livestock if they are avail¬able in surplus quantities. They contain trypsin inhibitors and must be cooked (Panigrahi and Francis, 1982). Arrowroot (Maranta arundinacea) is another trop¬ical tuber with potential as a feedstuff (Erdman and Erdman, 1984).
Aroids are root crops that grow in swampy areas of the humid tropics. Co-coyams or taro (Colocasia esculentd) is grown quite extensively as a food crop and may have potential as an animal feed. Raw taro contains crystals of calcium ox-alate, which have a strong irritant effect on mucous membranes of the mouth and digestive tract. Boiling the raw taro lowers the oxalate content and eliminates the growth-inhibitory effect of raw taro when included in poultry diets (Ravindran et al., 1996).
Jerusalem Artichoke There has been sporadic interest in the Jerusalem artichoke (Helianthus tuberosus) as a food and feed crop and, most recently, for fermentation to produce ethanol for fuel consumption. The plant is neither an artichoke nor from Jerusalem. It is a member of the sunflower family and is na¬tive to North America. The taste is said to resemble that of the true artichoke, and Jerusalem is a corruption ofgirasol, the Italian name for sunflower. The plant grows to a height of approximately 6 feet, and the flowers are similar to those of sunflowers, but smaller. It produces irregularly shaped knobby tubers that are rich in inulin, a polysaccharide composed of fructose. Although animals do not produce an enzyme to digest inulin, it is hydrolyzed by acid in the stomach (Gra¬ham andAman, 1986). Both the tubers and the vegetative matter can be used as feed, but the plant appears to have little to offer to justify its use in place of tra¬ditional crops.
Farnworth et al. (1995) found that dietary Jerusalem artichoke reduced the fecal odor of pigs. Polymers of fructose (fructans or fructooligosaccharides) are growth factors for bifidobacteria, whereas they cannot be fermented by many common gut microbes. Changes in gut microbes can alter fecal odor, which is caused largely by the compounds produced by intestinal bacteria.
Vegetables and Fruit A number of other succulent materials that serve primarily as energy sources include cull fruits and vegetables, such as onions, pumpkins, apples, and pears. In the Pacific Northwest of the United States, cull onions are used fairly extensively as a winter supplement for sheep and cattle. They contain n-propyi disulfide, which can induce hemolytic anemia in animals, and so should be fed at levels not exceeding 15 percent of the total diet. Another hazard associated with onion feeding (and with other material of a similar size) is the possibility of choking or blockage of the esophagus.
At one time, pumpkins and squash were grown as animal feeds and were of¬ten interplanted with corn. This practice is no longer economically viable (or practical with the use of mechanical corn harvesters).
Large quantities of reject bananas (Musa spp.) are available for feeding purposes in many tropical countries. Green bananas are somewhat unpalatable because of their tannin content (Dhua and Sen, 1989). Better results with non-ruminants are usually obtained with ripe fruit. Like cassava, bananas are low in
70 FEEDSTUFFS AND THEIR PROPERTIES
crude protein and high in starch and so serve primarily as an energy source. Pond and Maner (1984) summarized a number of studies indicating that, with proper protein supplementation, banana fruit can replace most or all of the grain in swine diets without adverse effects on performance. Preston and Leng (1987) empha¬size that it is better to feed ruminants the green fruit, while the carbohydrate is still in the form of starch rather than sugars. The skin (peel) is rich in tannins, which might have some value in ruminants by decreasing rumen degradability of dietary protein. Bananas are deficient in fermentable nitrogen, which can be read¬ily supplied with a urea supplement. By-pass protein can be provided with pro¬tein-rich legume foliage (e.g., leucaena, gliricidia) or with cottonseed meal. Plan¬tains are similar to bananas in appearance and feeding value, although they are somewhat higher in dry matter and starch content.
The foliage of bananas can also be used as feed. Bananas have a pseudostem that is quite digestible in ruminants. The leaves are tough and fibrous but are con¬sumed by livestock and can be used as a roughage source. The stalk, which is very high in cellulose and low in crude protein (7 percent) has limited value as a roughage source in ruminants, being equivalent to tropical grass hay in feeding value (Viswanathan et al., 1989). Enset {Ensete vertricosuni) is a large banana-like plant grown in Ethiopia as a food crop. The leaves and pseudostem are sim¬ilar to those of the banana in terms of feeding value for ruminants (Fekadu and Ledin, 1997).
Breadfruit meal, prepared by drying the fruit of the breadfruit tree (Arto-carpus communis), is an excellent source of starch and can replace corn in poultry diets (Ravindran and Sivakanesan, 1995).