Passage 1Of Ducks and Duck Eggs　　For people who like to keep poultry, ducks offer certain advantages over hens. Ducks are immune to some common diseases found in hens and are less vulnerable to others. Some breeds of duck produce bigger eggs than hens. In addition, ducks lay eggs over a longer season than hens do.　　Poultry keepers with gardens have less to worry about if they keep ducks rather than hens because the former are less apt to dig up plants and destroy roots. While both hens and ducks benefit the garden by eating pests, hens are known to damage herb and grass beds. Ducks, on the other hand, will search for insects and snails more carefully. Only very delicate plants are at risk from the broad, webbed feet of ducks.　　Like all waterbirds, ducks need access to water, and duck keepers typically provide this by building a pond. Something this large is not absolutely necessary, however, ducks need only to be able to dip their heads in the water to keep their nostrils clean. If a pond is provided though it is important to keep ducklings away from it until they are old enough to withstand the cool temperature of the water-about eight weeks.　　When keeping ducks, one has to consider just how many the land will support. Generally the rule is 100 ducks per-half hectare. If more than this proportion is introduced, there is a risk of compacting the soil, which can lead to muddy conditions for long periods as the rain is not easily absorbed into the ground.　　While ducks offer many advantages over hens, they must be given greater quantity of food, especially if regular eggs are desired. An adult duck will eat between 170 to 200 grams of food a day. If the ducks have access to grass and a pond, they will be able to find for themselves approximately 70% of their daily dietary, requirements in warmer months but less than half that in colder times. Therefore, it is important that they are fed enough food, such as grain, every day.　　Experienced duck keepers raise ducklings every three years or so because it is after this period of time that ducks’ egg-laying powers begin to seriously weaken. If the aim is to hatch duckling, keepers should be aware that not all ducks make good mothers, and that certain breeds of duck appear to be worse than others. The poor mothers abandon their eggs a few days after laying them. A sure way of making sure the rejected eggs hatch is to place them next to chicken eggs under a hen.　　The eggs of ducks as food for humans have a mixed reputation. This is because of a number of cases of salmonella food poisoning in Europe in the 1970s. Although it was never conclusively shown that duck eggs were to blame, the egg-eating public stopped buying and many duck egg producers went bankrupt. Indeed, there is a risk of salmonella poisoning when ducks lay their eggs in damp conditions, such as on ground that is constantly wet but the same can be said for the eggs of hens. And commercial duck egg production in France and England, where the out-breaks of salmonella poisoning took place, followed the same standards as those used in the hen egg industry, which experienced no salmonella problems. (Storage of eggs, whether those of hen or duck, can also be a factor in contamination. Studies have found that bacterial growth reaches potentially dangerous levels at storage temperatures of 5℃ or greater.)　　The salmonella scare was over by the early 1980s, but, at least in smaller markets like Australia and New Zealand, few producers wished to risk investment in ducks for fear of problems. No large-scale commercial duck egg production exists in these countries. It has thus been left to small producers, and, more commonly, home duck keepers.　　Classify the characteristics listed below as belonging to　　D         Ducks　　H         Hens　　B         Both ducks and hens　　NI        If there is no information in the reading passage　　Write the appropriate letters in boxes 1-8 on your answer sheet.　　1. lengthier laying period　　2. better mothers　　3. less likely to uproot plants　　4. dangerous to grass　　5. more eggs per week　　6. eat more grain　　7. beneficial to garden by eliminating pests　　8. more vulnerable to illness

发布日期：2022-07-06

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