Ambient temperature
The amount of air around the herd is often considered to be a major part of the thermal environment. The suitable temperature range is called a temperature-appropriate zone or isothermal zone. The lower effective ambient temperature of the isothermal zone is called the lower critical temperature (LCT). In this temperature range, the animal's body temperature remains relatively constant, and if there is no other stress (such as disease), the animal's metabolic intensity and heat production are normal. For pigs, the exact LCT value depends on the feed intake and body weight. LCT values ​​were lower in pigs that consumed more food than those fed less. The upper effective ambient temperature is called the upper critical temperature (UCT) or the critical temperature for vaporization. Once the temperature is higher than UCT, the herd begins to pant or is restless and at the same time radiates heat to the surroundings to maintain normal body temperature.
Air temperature is not the only component of the thermal environment. Other factors can also affect the heat exchange between the herd and the surrounding environment, including the surrounding air flow rate and the ground type of the pig house. In production, how to solve the impact of these factors on the pig's thermal environment is also very important. The effective ambient temperature has a regulating effect on the temperature and other factors in the thermal environment. For example, at a constant temperature, the herd feels warmer in a litter-free pig house than in a littered pig house, and the effective ambient temperature is lower in a littered pig house. Therefore, in a litter pig house, the air temperature needs to be increased to compensate for the chill effect caused by the moisture contained in the litter. According to various factors affecting the thermal environment, it is necessary to properly adjust the air temperature, which is usually referred to as a set temperature value. By setting the temperature on the air temperature control sensor, a comfortable thermal environment is provided for the growth of the pigs. The set temperature is usually set according to the air temperature.
Gas in the environment
Modern facilities in enclosed piggery include excreta disposal systems, ventilation systems, and overall facility management to improve indoor air quality. Ammonia levels are often used as an indicator of air quality. Some scholars have suggested that the optimum ammonia concentration should be controlled within 10 mg/l, which is achievable in piggery with good ventilation system. According to the National Institute of Occupational Safety and Health (NIOSH), the average concentration of ammonia in the working environment of livestock farms is 25 milligrams per liter. According to the U.S. Government’s Industrial Hygiene Committee, the ammonia concentration limit in the working environment of livestock farms must not exceed 25 mg/l for livestock workers working from 8 hours to 10 hours per day. When the livestock farm workers concentrate their operations, the concentration of ammonia in the air shall not exceed 35 mg/L within 15 minutes.
The underground pit is a storage pit that stores feces under the floor of a pig house. The facility can keep the average ammonia content below 10 mg/l for years, but sometimes the ammonia concentration is as high as 50 mg/l in hours or days. Or higher. As mentioned earlier, the limit for exposure to ammonia in pig farm workers in the short term (15 minutes) is 35 mg/l.
Underground pits can also reduce H2S in the air. When H2S concentration reaches 1 mg/l, most people can smell it. With the increase of hydrogen sulfide concentration, when people reach 50 mg to 100 mg/l, people often lose their sensibility. When the concentration of hydrogen sulfide exceeds 500 mg/L, it is fatal. Therefore, hydrogen sulfide is a huge source of danger, and when it does not smell the smell of hydrogen sulfide, it may have reached a lethal level. Hydrogen sulfide content is usually very low in pig houses with underground storage pit systems.
At present, the ventilation system of the piggery has been widely used. The key lies in the design and actual operation of the ventilation system. Ventilation and ventilation are required in any season of the year. Ventilation requires continuous and uniform ventilation. Ventilation rates need to be kept constant and adapted to the season at the time. The specific amount of ventilation required depends on the weather conditions outside the home. The ventilation system needs to have a control and management system to facilitate changing the ventilation rate in the entire pig house. The ventilation system can significantly reduce the amount of dust in the building. If the air exchange is greater than the required humidity, the house will tend to dry and the dust concentration will increase. Relative humidity content should be 40%~70%. In winter, relative humidity should be 60% to 70% under most weather conditions. Within this range, while minimizing the ventilation rate, animal heat consumption is also reduced, and the herd is still healthy. It has been confirmed that high dust levels are not conducive to the health of pigs and humans. Dust levels can be controlled by proper ventilation.
The use of an appropriate feed treatment system can reduce the dust generated during the feed treatment process. Feed processing technology also affects the dust level of closed pig houses. Finally, the full-entry production model in facility management practices has been shown to improve the health and growth performance of herds. The all-in, all-out system can improve indoor air quality because after the animals are emptied, the site is thoroughly cleaned before the new herds are moved in. In this way, since the dust left over from the previous cycle is removed, the dust level in the home is greatly reduced after the start of the new feeding cycle.