1. The anatomical characteristics of chickens lead to frequent respiratory diseases. Chickens and birds are common ancestors. In order to adapt to the needs of flying, chickens and birds have a unique physiological structure-airbags. The air sacs communicate with the outside world and are distributed around the internal organs of the body. They are close to or even close to the heart and liver. The existence of this structure will not cause any inconvenience to chickens in a clean wild environment. However, domestication, especially for intensive chicken production, the existence of air sacs has become the basis for the easy occurrence of respiratory diseases. The dirty air in the house reduces the frequency of respiratory cilia, destroys the integrity of the respiratory mucosa, and causes a large number of pathogens. Microorganisms invade the body and settle in air sacs. In the case of good physique and strong disease resistance, they will generally not cause serious harm, but when weather changes, immunity, swarming, beak breaking and other stress or other diseases exist, When the disease resistance of chickens is reduced, conditional pathogenic microorganisms such as Escherichia coli and mycoplasma that invade the body will multiply. Because the air sacs are close to the internal organs, and there is no septum between the chest and abdomen, it will soon cause systemic sepsis such as "perihepatitis" and "pericarditis".　
　Second, the poor breeding environment is responsible for the anatomical characteristics of the chicken, which puts more stringent requirements on the environment. Ammonia in the chicken house should not exceed 10 mg per cubic meter, and the adult chicken should not exceed 15 mg; the hydrogen sulfide chicken house should not exceed 2 mg, and the adult chicken should not exceed 10 mg; the carbon dioxide should not exceed 1500 mg per cubic meter; the odor dilution factor should not exceed 70 . The field and living areas outside the chicken house require that the content of the above substances is low; the inhalable particulate matter in the air in the chicken house does not exceed 4 mg; the total suspended particulate matter does not exceed 8 mg per cubic meter, and the number of microorganisms should be controlled at 250,000 per cubic meter Below this, dust in the air is an important carrier of bacteria. In reality, many farmers ignore the physiological and anatomical characteristics of chickens and fail to create good environmental conditions for the survival of chickens. The main manifestations are: improper site selection of chicken farms, unreasonable construction of chicken coops, no scientific ventilation system, lack of attention to ventilation, lack of ventilation, and lack of ventilation. The chicken farms are low-lying and the environment is narrow. Some build farms in the woods or plant a lot of trees in the farms, so that the wind cannot enter and harmful gases can not be discharged; the distance between the chicken coops is too narrow, the airflow cannot flow well, and the window settings are unreasonable. There is no floor window or skylight, the air is not convective, there is no ventilation equipment or the setting is unreasonable; some are afraid that the chickens will not ventilate when they are cold or frozen (don’t forget that the chickens have feathers, which can be adjusted by the growth of feathers. The outside temperature changes, there are no chickens that freeze to death, only poor ventilation causes the death of the chickens); some people have no ventilation because of a ventilated disease. "Ten years of fear of well ropes" are no longer ventilated. All this makes chickens live for many years in an environment of hypoxia, ammonia, hydrogen sulfide gas, methane, carbon dioxide and other gases seriously exceed the standard. Outside pathogenic microorganisms are not only easy to invade the body and cause chicken disease, but also often have poor ventilation and tissues. Hypoxia, decreased heart and lung functions, insufficient oxygen in the blood, and the body is in a pathological state, unable to produce a good immune response to immunity. We often attribute the occurrence of respiratory diseases after ventilation to this ventilation, but this is not the case. Often 2-3 days before the weather turns warmer or the weather is clear, there is no wind. At this time, if we close the chicken house, the air inside and outside is not circulating, the harmful gas in the chicken house exceeds the standard, and pathogenic microorganisms are easily infiltrated into the body and cause disease. During the incubation period, when the weather gets warmer, the ventilation is not gradual, and the subsequent occurrence of respiratory diseases, which means that the windless days before the weather changes are the chicken’s "black Sundays." Therefore, ventilation is one of the most important issues in chicken feeding and management.　　3. Really do a good job of ventilation　　The chicken farm must choose a place with high dryness, flat, sunny leeward, open, and good ventilation. The layout of the chicken coops should be reasonable. The orientation of the chicken coops should be at an angle of 30°-45° with the prevailing wind direction throughout the year to avoid zero-degree wind incidence angle. The buildings of the upwind chicken coops should not be too high, and the distance between the chicken coops should be at least 3-4 coops high. The size of the door is generally a single door is 2 meters high and 1 meter wide, and two doors are 2 meters high and 1.6 meters wide. The windows of a semi-open, open chicken house should be installed on the front and rear walls, and the front windows should be wide and lower from the ground to facilitate lighting. The ratio of window to floor area is 1:10-1:8. The rear window should be small, about 2/3 of the area of the front window; in each house, a floor window with a width of 50 cm and a height of 30 cm should be set at a distance of 5-10 cm from the ground; The inflator with a diameter of 20-30 cm, the inflator should be open all year round. For chicken farms that cannot be mechanically ventilated, as long as there is no ice in the house, do not close the skylights, and allow the chickens to gradually adapt to the cold climate to promote the growth of feathers; for mechanical ventilation equipment, always pay attention to ventilation to ensure that the air is fresh; Pay attention to strengthening ventilation on days when there is no wind 2-3 days before the weather turns warm. On the day of warming, the ventilation volume must be gradually increased; on the windy days before the weather turns cold, pay attention to closing doors and windows as soon as possible. On that day, there is no wind outside, but more attention should be paid to ventilation. The principle of ventilation is: if there is no wind, it will pass, and if there is wind, it will decrease. Conditional chicken farms should set up a space electric field control network to make the removal efficiency of the number of microbial colonies in the air reach 90%-99%. The chick house should also have an exhaust pump, and keep the skylight unobstructed from the first day of entering the chicken. It is best to have mechanical ventilation equipment, and turn on the fan for ventilation after the temperature rises 2 ℃-3 ℃, and complete the ventilation before the temperature drops. ; Open windows for ventilation when the outside temperature is high from 10 to 15 every day. Keep the air fresh under any circumstances. When there is a conflict between heat preservation and ventilation, it is better to sacrifice heat preservation and ventilate.