Generally high temperatures in summer, especially in southern China, the temperature is usually between 30 °C ~ 35 °C, the humidity is often higher than 70%, and the duration is longer, up to 4 months. Pigs are warm-blooded animals, with thick subcutaneous fat and underdeveloped sweat glands. Therefore, the feed intake, daily weight gain, feed utilization rate, sow fertility rate, and litter size of the pigs in the high temperature and high humidity environment in the summer, boars Sperm quality, piglet survival rate and other production and reproduction performance have a great impact. Production practice has proved that when the ambient temperature reaches above 30 °C, if no cooling measures are taken, all kinds of pigs (except suckling piglets) will be in a state of heat stress, and the health status and production performance of pigs will be greatly affected: The sows did not have estrus, and the conception rate and litter size were significantly reduced. The sows showed irritability, decreased feed intake, decreased milk production, and more weight loss. The piglets were born with lighter weight, lower weight gain, and lower survival rate. The breeding ability of male boars for mating and sperm production declines; fattening pigs are susceptible to heat loss, growth stagnation, feed utilization, pigs' daily weight gain, and even death from heat stroke. Therefore, in the summer hot season, it is necessary to strengthen the work of preventing heatstroke, control the environmental temperature in the pig house, ensure the safety of live pigs, and improve pig breeding efficiency.
1 Temperature requirements for various herds
The requirements for ambient temperature are different for all types of herds. The suitable growth temperature for newborn piglets is 34 °C to 35 °C; the suitable growth temperature for piglets at 3 to 4 weeks of age is approximately 30 °C; the suitable growth temperature for slightly larger piglets is 20 °C. °C ~ 23 °C; suitable temperature for growing pigs is 17 °C ~ 22 °C. We can see that except for piglets, the suitable temperature for all types of pigs is below 30°C, which is much lower than most regions in China, especially the summer temperatures in the southern region (between 30 °C and 35 °C). Therefore, In order to ensure the normal production of the farm in summer, the pighouse must be cooled, and due to the different temperatures required by various herds, the cooling method must also be determined according to the actual situation.
2 Cooling measures for pig houses
In recent years, domestic and foreign research and development of a variety of cooling facilities suitable for different herds have been widely used in intensive pig production, greatly reducing summer heat stress in closed rearing environments and realizing large-scale pig farms. Balanced production throughout the year provides protection. The means of cooling the piggery include thermal insulation of the external protective structure, thermal insulation design of the pig house, and cooling equipment of the barn.
2.1 Design of building insulation in pig houses
At present, in the production practice, the heat insulation and heatstroke prevention design of the pig building is based on the local climate characteristics, and the direction and spacing of the pig house are properly constructed. The exterior of the pig house is painted white with lime water in order to improve the reflectivity of the exterior of the pig house. Heat loss rate, thus reducing solar thermal energy transmission to pig houses and pigs, adopting roofing materials with smaller thermal conductivity or adopting roof insulation design with multi-building structures, etc. The wall insulation design uses hollow bricks instead of ordinary clay bricks. As a wall material, its thermal resistance can be increased by 41%, while the use of air-entrained concrete blocks can be increased by 6 times. The use of a double wall can also greatly increase the thermal resistance of the wall. Planting trees, climbing plants or sheltering the sun with reeds, curtains, roofs, etc. directly into the pig house.
2.2 Ventilation
In summer, effective ventilation of the pig house can remove the heat in the pig house, which has a certain effect on lowering the house temperature. At present, there are two kinds of natural ventilation and mechanical ventilation. Natural ventilation is to set appropriate air inlet and outlet in the pig house building. The natural air and temperature difference are used to introduce fresh air into the house, and the excess heat and pollutant gas in the house will be discharged outside. Mechanical ventilation currently uses vertical ventilation. The fan is installed on the hill of a pig house for vertical ventilation. The high-temperature air in the house is exhausted by a fan, and cool fresh air is introduced into the room. Ventilation plays a better role in the pig house.
When the outside temperature is significantly lower than the body temperature of the pig, ventilation can effectively dissipate the body heat of the pig. However, if the air temperature is higher than 25 °C, the cooling effect of ventilation will be significantly worse. When the temperature reaches 30 °C or more, the ventilation alone Can not effectively reduce the temperature within the home. Therefore, when the temperature is high, you should consider cooling the air and then sending it into the pig house. Such as the use of underground pipes, tunnels, etc. for ventilation and cooling, outside the air can be first entered underground pipes, tunnels or natural caves, and then into the pig house, you can reduce the outside air 3 °C ~ 5 °C, temperature and humidity less than 85% . In order to ensure the effectiveness of tunnel ventilation and cooling methods, tunnels with deeper excavation are often required, with depths of up to 3 to 4 m, and sufficient lengths. Therefore, the amount of work is large, and the input is also relatively large, close to the artificial refrigeration system, but The operating cost is very low. If ready-made tunnels such as abandoned mines and natural caves can be used, one-time investment will be greatly reduced. This system can also have the effect of heating in winter and reduce the temperature changes in the four seasons of the pig house. .
2.3 Evaporation and cooling
The cooling of closed piggery in foreign countries mainly depends on the wet curtain-fan cooling system, or mechanical ventilation to assist local cooling, such as setting spray, shower, drip system, or combined with underground pipe ventilation for cooling. China is also researching and applying in these aspects. At present, the evaporative cooling systems that can be used in livestock and poultry houses in China include wet curtain fan cooling system, spray cooling system, and spray cooling system. All of them are evaporative cooling technologies that use water evaporation and heat absorption to achieve cooling. Evaporative cooling has the advantages of significant effect, energy saving, less one-time investment, reliable operation and easy maintenance. Not only applies to China's dry northern regions, but also applies to most areas in southern China.
1) Wet curtain fan cooling system
Wet curtain fan cooling has been used in many agricultural buildings, and the effect is also very significant. It has been used in summer cooling of livestock and poultry houses and has achieved good results. In 1988, the eastern school district of China Agricultural University successfully developed a wet curtain fan system suitable for China's conditions. , And together with the 9FJ series fans are included in the national new products to promote the application of the country, this technology and vertical ventilation technology, has become the best mode of ventilation ventilation in the summer of agricultural buildings. Wet curtain fan cooling system consists of wet curtain fan, water circulation system and control device. The core part is wet curtain. The specific design is to install the wet curtain on the gable at one end of the pig house, and the fan is installed on the other end of the mountain wall. When the fan draws air, negative pressure is generated in the house, so that the outside air is cooled down through the wet surface of the wet curtain. The actual use test shows that the wet curtain has a thickness of 12 cm, and when the curtain wind speed is 1.0 to 1.2 m/s, the wet curtain cooling efficiency is 81% to 87%.
The wet curtain-fan cooling system has the advantages of simple equipment, low cost, low energy consumption, large production capacity, reliable and convenient operation, and automatic control. It is suitable for use in pig farm breeding houses, breeding boars, gestation houses and finishing pig houses. When the temperature outside the house reaches 35 °C ~ 37 °C, the wet curtain fan system can reduce the temperature inside the house to below 30 °C, while the temperature of the pig house with only the fan cooling is up to about 33 °C. In addition, the use of wet curtain fan cooling system in the pig house is also significantly reduced, the health environment improved, greatly improving the summer of the high temperature season pig welfare. During use, attention should be paid to the maintenance of the wet curtain to prevent scaling and rodent damage.
2) Spray cooling system
The spray cooling system can be divided into a spray spray cooling system and a roof spray cooling system according to different spray installation positions. The cooling in the house spray is the installation of sprinklers above the swine's active area, spraying the water directly to the pigs at regular intervals, and evaporating the water on the surface of the pig's body to remove the heat. This type of cooling system is simple in equipment, equipment investment and operating costs are very low, but it is easy to cause water in the area, increase the humidity inside the house, so pay special attention when using this type of cooling method, generally take intermittent operation, according to the actual temperature, Humidity and ventilation conditions determine the interval time and spray time, usually interval 45 ~ 60 min, spray 1 ~ 2 min. Roof spraying refers to the installation of a sprinkler system on the roof. The use of a sprinkler to spray water forms a water film that vaporizes and evaporates to achieve cooling. The disadvantage is that it is easy to form scale deposits and the amount of water is large.
3) Spray Cooling System
The use of high-pressure nozzles to atomize water droplets into droplets with a diameter of 50-80 μm or less enables the water droplets to completely evaporate before they fall on the surface of the animals or the ground, thus absorbing the heat in the room and achieving the purpose of cooling. Foreign studies have shown that the use of high-pressure spray system in cooling pigs and weaning sows in summer has a good effect on cooling, and the cooling rate can reach 5 °C and can also reduce dust in pig houses. Another spray cooling system is the centralized fine mist cooling system. This method is also called the boiling furnace type centralized atomization cooling system. The spray chamber is set at the air inlet of the building to carry out centralized spray cooling to make the droplets produce similar to industrial boiling furnace powder. The movement of the particles increases the contact time between the air flow and the water droplets, improves the cooling effect, and the unevaporated droplets can fall into the collection basin for recycling, avoiding the problem of direct spraying to wet the pig's surface and the ground in the chamber. The requirements of the spray device are also greatly reduced. The system is equivalent to installing a spray chamber outside the suction port instead of the wet curtain. Our scholars have shown that the outdoor relative humidity in the summer is 55% to 60%. In the common case where the temperature difference between wet and dry bulbs is about 6 °C to 8 °C, the concentration of fine mist cooling device can reduce the air temperature entering the house by 5 °C ~ 6 °C, and the average temperature inside the house is about 4 °C lower than that of the outside house. The humidity is generally not higher than 80%. American scholars reported that the investment in the fine mist cooling system is relatively low (in the United States, it is equivalent to about half of the temperature of the wet pad cooling system), and the adaptability is wide. The closed and open houses, mechanical ventilation and natural ventilation can all be adopted, and the flexible use and spraying facilities can be used. Can be used for disinfection. However, the cooling efficiency of fine mist cooling is still lower than that of wet mats. The main reason is that the distribution of fine mist is not uniform, and some spaces are not well distributed due to the distribution of droplets.
In various means of cooling in summer, evaporative cooling is the most economical. Inadequacies in the cooling will also increase the humidity, which is determined by the principle of cooling, and it is difficult to overcome the defects, so in the weather with high humidity Can not achieve a good cooling effect, so to make use of the potential to evaporate cooling within these limits, is the difficulty of evaporation cooling technology. Although it has its limitations, it can solve the main contradiction of high temperature in agricultural construction in summer and it is economical, so it is still an effective cooling method for agricultural construction in summer.
2.4 Local cooling system of pig house floor
This type of cooling system refers to a conductive cooling method that uses underground water as a medium to lay pipes in the lower part of the floor of a pig's reclining area. It is suitable for areas with groundwater sources and where wells can be drilled. Because the system is locally cooled, it is not only suitable for fattening pigs, pregnant sows and other large pigs, but also suitable for the cooling of sow activities and reclining areas of nursing houses. Not only closed pig houses, but also environmental protection can be applied to open houses. The application of one of the measures is conducive to improving the feeding environment of pigs, reducing the impact of high temperature on the productivity of pigs, and has the advantages of simplifying the building structure, reducing construction costs and production costs. The actual measurement shows that, when the temperature outside the house is as high as 34 °C, the temperature of the groundwater floor cooling area does not exceed 26 °C, and it is generally stable at 22 °C to 26 °C.
3 Conclusion
To sum up, in order to ensure the normal production of the summer farms, it is necessary to conduct temperature management according to the temperature requirements of various types of herds in summer and take effective cooling measures. However, it should be noted that any kind of cooling measures have some drawbacks. For example, although the cooling of the shower is simple and effective, the water consumption will cause the water in the area to be built, which will lead to an increase in the environmental humidity. It is not suitable for the branch house and the piglet. Although the cooling effect of the curtain is better, it is greatly affected by the outside humidity, and there are problems such as the high cost of the paper curtain, the adhesion of the grime and the deposition of the salt, and the like. The centralized fine fog cooling system is only applicable to closed pig houses. The local environment jet control spray evaporation cooling system is only applicable to open type pig houses. The local cooling system of the pig house floor only cools the floor. Therefore, in order to ensure the smooth production of pig farms during the summer hot season, in addition to the above-mentioned cooling measures, it is necessary to make appropriate feeding and management, such as improving the formula of the diet, adequate drinking water, small-group rearing, and lowering the rearing density. Wait.
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