Effect of airflow on pigs

The motion of air molecules is called air flow, and the air flow that moves horizontally is called wind. The air flow in the atmosphere is caused by the uneven temperature distribution on the earth's surface, and the air molecules flow from the region of low temperature and high pressure to the region of high temperature and low pressure. In weather, the wind speed and direction are often described. The wind speed is the distance of the wind movement per unit time (m); the wind direction is the direction of the wind, expressed in 8 or 16 directions, and the wind direction frequency chart (wind direction rose chart) is drawn according to the probability of the wind appearing in each direction. The wind direction frequency diagram can clearly show the main wind direction in a certain area in a certain period of time, which is the basis for the site selection of the pig farm, the layout of the buildings in the farm and the design of the pig house.

There is also a difference in air pressure in different areas of the pigsty, which also forms an airflow. Under natural circumstances, the strength of the air flow in the house is affected by two factors: one is the wind pressure, that is, the wind outside the pigsty flows through the windward doors, windows or holes, and the other is hot pressing, that is, the temperature inside the piggery is generally higher than that outside the house. the air entering the house moves upward when heated and flows out from the skylights or the upper part of the doors and windows. If the fan is used as the ventilation power, the direction and size of the air flow depends on the number of fans, flow, location, air intake and so on. In addition to considering the wind direction and speed, the ventilation volume (ventilation volume) is an important indicator, which is generally expressed by the volume of fresh air per unit or unit live weight (1kg or 100kg) per hour; it can also be expressed as the amount of air exchange per unit time is a multiple of the volume of the pig house, which is called the number of air exchange. The direction of air flow in the pigsty can be determined by smoke, and the wind speed can be measured by cataract thermometer or hot ball anemometer.

Airflow, together with other thermal environmental factors, affects the thermal regulation of pigs, which in turn affects their productivity and health. When the air temperature is lower than the skin temperature, the air flow can promote convection and heat dissipation, and at any other temperature, the air flow can promote evaporation and heat dissipation. therefore, the air flow at low temperature is disadvantageous to the regulation of body heat, while the air flow at south temperature is beneficial to the body heat balance. however, when the air temperature is higher than the skin temperature (especially when the relative humidity is high), the high wind speed has an unfavorable trend to the body. The results showed that when the air temperature was constant, the ambient wind speed of piglets increased from 0.1m/s to 0.3m/s, which was equivalent to a decrease of 5 ℃ in ambient temperature. Someone trained pigs to turn off the fan press switch in the artificial climate room. It was found that the time for pigs to allow the fan to supply air increased as the temperature increased from-5 ℃ to 40 ℃; when the ambient temperature reached 30 ℃ or higher, the pig no longer turned off the fan, indicating that the air flow is beneficial to the pig at high temperature. In addition, ventilation can eliminate water vapor and harmful gases such as carbon dioxide, ammonia and hydrogen sulfide in the house, ensure dryness and improve air hygiene. Therefore, pig houses need to be ventilated in any season, especially in winter, doors and windows are often closed in order to prevent cold, resulting in dampness and deterioration of air hygiene, so proper ventilation must be paid attention to. Ventilation and heat preservation are a pair of contradictions in winter, and qualified enterprises can control ventilation according to the humidity requirements of pig houses under the condition of meeting the temperature supply; in order to reduce costs, ventilation measures should be taken to ensure that the ambient temperature of pig houses can be basically satisfied, to prevent the invasion of thieves and endanger the health of pigs.