Heat stress and control of pigs in summer

Heat stress refers to the sum of the non-specific physiological responses of the body to any demands placed on the body by the hot environment at extreme high ambient temperatures. With the rapid development of intensive and high-density rearing methods, most southern regions are increasingly pressing for alleviation of the environmental pressure caused by high summer temperatures on the pig industry. The northern climate also has an increasing trend. The highest temperature in Beijing in recent years is also Arrived more than 40 degrees. The decline in productivity of pigs due to heat stress is also increasingly attracting the attention of livestock researchers and feed nutrition researchers. Scholars in Japan, the United States, and Britain have conducted research in this field in the 1950s and 1970s. Chinese scholars started late and have been involved in this field since the early 1980s to seek regular changes in heat stress to animals, to reveal the influence of thermal environment on pig productivity, and to develop measures to mitigate the effects of heat stress. First, the reasons for the occurrence of (a) the pig is a constant temperature animal, thick subcutaneous fat, sweat glands are not developed, the body emits slower heat, not good at regulating body temperature through skin evaporative heat, so the pig is not heat-resistant. Feeding practice has proved that the optimum temperature of pigs decreases with increasing body weight and age. The suitable temperature for newborn piglets is 27-29 degrees, 21-24 degrees for weaned piglets, and 15-25 degrees for growing pigs. Sows are 16 to 18 degrees. In the optimal ambient temperature range, the heat production and heat dissipation of the pigs maintain a dynamic balance, so the body temperature of the pig is kept constant, the feed utilization rate is high, the growth rate is fast, and the disease resistance is strong. (b) When the ambient temperature exceeds the optimal temperature range, the pig's heat production is greater than the heat dissipation. Pigs must adjust body temperature balance by increasing respiratory evaporation and radiative heat dissipation, or by reducing intake and thereby reducing body heat production. If the body temperature balance cannot be maintained by increasing heat dissipation and reducing heat production, the body temperature of the pig will rise. Foreign scholars reported that 18--28 kg of piglets at body temperature of 35 degrees from the normal body temperature increased by 1.4 degrees, weighing about 60 kg of Barkshire boar at ambient temperature of nearly 30 degrees can not maintain normal body temperature. Pigs that have been exposed to high temperatures for a long period of time, if too much heat is accumulated in the body and can not be dispersed, it is easy to keep the body temperature high, leading to changes in the neuroendocrine system of pigs, causing heat stress or even heat stroke. The heat-resistance of pigs is related to such factors as breed and size, weight, and economic type. The smaller the body is, the more heat-resistant, but now most of the varieties in China develop outwards to three yuan, and the growth rate is faster, and it is more prone to heat stress. (3) With the large-scale intensification of the swine industry, the density of herds has further increased, and the use of the bail brackets and the promotion of high-bed delivery rooms have made pig farms more sensitive to high-temperature seasons. (4) Many ranch owners pay more attention to the cold and warmth of the pig farm in winter, and are also willing to invest in it; but the emphasis on the high temperature in the summer and the investment in equipment reform are insufficient. Second, clinical manifestations and changes (a) performance. The pigs with a heat stress reaction are depressed, have elevated body temperature, have a rapid heartbeat, and have shortness of breath and even hot wheezing. Eat less, like drinking water, reduce the amount of activity, stretch the body, sleep wet or urine. Avoiding direct sunlight or tending to a cool place, the blood vessels of the skin dilate and the skin temperature rises. Slow growth or stagnation, gradually thinning. (b) Changes in the body. Boar libido weakened, ejaculation volume decreased, sperm motility decreased, and the ratio of live sperm to total sperm decreased. Young sows have delayed puberty and sexual maturation, delayed sows' estrus, and hidden estruss are not even estrus. Ovarian function and sexual function decline, conception rate decreased significantly. When the temperature reaches 32 degrees or more, the sows are bred. About 20% of the pigs are infertile or repeat estrus and the abortion rate increases. The high temperature significantly reduced the survival of the embryos within 8 days after mating, followed by the embryos within a few days (11 to 20 days after conception), and was particularly sensitive to heat. After 20 days, it had stronger heat resistance. Sows can have serious reproductive problems when they are heated during the second trimester of pregnancy. In summer, the number of litters and live piglets in the sow are reduced by 1–2, the sow’s lactation is reduced, the suckling pigs have poor growth, the survival rate is low, and the weaned piglets have a small body weight. (III) Effect of heat stress on pig growth The most suitable growth temperature for growing-finishing pigs ranges from 18 to 21°C. It is generally believed that 32-38°C is the range of heat stress. Experiments show that when the ambient temperature is higher than the optimum temperature of 5 ~ 10 °C, the pig's feed intake will have to reduce 6% to 21%. . Heat stress causes the feed intake of pigs to decrease, and daily gains decrease. The reason can be explained as follows: (1) As the heat stress changes the normal activities of growth and fattening pigs in the body, it leads to disorders of hormone secretion such as thyroxine and epinephrine metabolizing substances, which causes the body's sugar and fat. The metabolic activity of the class and protein is reduced, which in turn reduces the pig's daily gain rate. (2) High temperature causes a decrease in the excitability of the feeding center, resulting in a decrease in feed intake. The high temperature causes a decrease in feed intake, and the decrease in nutrient intake is the direct cause of the decrease in pig weight gain. (IV) Effects of heat stress on reproductive function of sows 1. Sow: Under heat stress conditions, sows showed decreased ovarian function, decreased conception rate, increased number of stillbirths at the end of pregnancy, decreased litter weight, and even miscarriage; The mating of pigs is weakened and semen quality is reduced. For boars, high temperatures lead to a higher proportion of pigs without mating than to normal season, and the amount of boar ejaculation decreases, the ratio between the total number of spermatozoa and spermatozoa decreases, the spermatogenesis of testis is impaired, and the multinucleated giant cells in semen As the temperature rises, the fertilization rate is 85% to 90% at 20°C and 50% to 60% after exposure at 33°C for 72 hours. The effect of heat stress on the reproductive function of pigs is explained by the fact that heat stress alters the normal state of endocrine function, causes abnormal thyroid function, changes in thyrotropin secretion, and a significant increase in adrenocorticotropic hormone in plasma. Heat stress blocks the use of thyroid hormone and causes the body's feedback inhibition of thyroid hormone production. Although the mechanism affecting reproductive function is not yet clear, at least it can be considered that pigs, after being exposed to persistent heat stress, indirectly affect ovarian function and, in severe cases, induce ovarian cysts. There is also a danger to the sow is that the loss of appetite, resulting in decreased feed intake, resulting in decreased sow milking and quality of the sow, eventually causing the diarrhea and slow growth of piglets in the delivery room, affecting the survival rate of piglets and weaning weight. 2, boar: hot can also increase the adrenal cortex hormones in the blood of the boar, so that the production of steroids in the testis is inhibited, resulting in reduced boar mating, high temperature denaturalization of sperm cells, semen will As a result of the continuous emergence of multi-nucleated giant cells fused by the affected cells, the quality of the semen dropped. The effect of high temperatures on the quality of boar semen can be extended even after 3 months. The reason for the large decline in sow return and litter size in the second half of each year is due to high temperatures. Third, control measures: From the following aspects to consider how to reduce the damage caused by heat stress. (A) to create a good environment, do a good job in the summer heat of the pig house: 1, insulation. The pig farm should be built in an open and ventilated area. The choice is to face north and south. In the south, an open or semi-open pig house is appropriate. Traditional open loop shelters or shade nets can effectively block the sunlight and reduce heat. Harm to pigs. In the northern area, closed-type pig houses are constructed with roofs coated with white paint or covered with thermal insulation, and ceilings filled with heat-insulating materials such as sawdust to increase the span of the houses. 2, ventilation. An adjustable roof ventilation window and ground ventilation window can also be built. In summer and autumn, the pig house door is converted into a ventilation door to enhance ventilation and eliminate harmful gases. Planting tall trees around pig farms and pig houses can reduce sunlight exposure and lower the environment and air temperature in pig houses. If the natural ventilation alone can not reduce the temperature, you can use mechanical ventilation, install a fan or blower to promote air flow, effectively reduce the air humidity, take away the heat. Longitudinal ventilation is better than lateral ventilation. 3. Spray (sprinkle) water. Evaporative cooling is the most effective method. When the temperature is too high, hose or sprayer can be used to cool the pig body (except the branch house) and the roof with water spray or artificial watering. The dripping water cooling system is available for the monomer limit bar and the farrowing house sow. The drip device is installed above the shoulder of the pig, and low-flow drips are used to cool the pig neck, shoulder and back skin at an interval of about 1 hour, resulting in significant cooling effect. However, the cooling rate of dripping water is slow, and the temperature of the whole pig house cannot be controlled well. For fasting and pregnant sows, growing pigs, and spraying in the summer or autumn in the hot weather, the cooling rate is fast, and the temperature in the house can be reduced by 5-8 degrees within 5 to 10 minutes, and the air can be purified. For boars, the testicles need to be flushed regularly. However, the biggest problem with spray (sprinkling) water cooling is that it will increase the humidity inside the house. On the one hand, high temperature and high humidity will aggravate the occurrence of heat stress; on the other hand, high humidity will also cause the spread of pathogenic microorganisms in the house. Especially in the delivery room to use spray water to cool down carefully and pay attention to the method. 4, wet curtain fan cooling. Wet curtain fan cooling system is an ideal cooling method that has risen in recent years. It began to appear in the country in the 1980s and was first used for the summer cooling of breeder houses. The principle is to install a curtain in the wall, and blow the curtain with a fan. Because the water evaporates and requires heat, the temperature of the blown air is lower than the temperature of the house. Cold air enters the house to reduce the temperature. When the wet curtain thickness is 12 cm and the curtain wind speed is 1.0 - 1.2 m/s, the temperature can be reduced by 5 - 7°C. The drier the air, the higher the temperature, the greater the air cooling through the wet curtain, the more significant the effect. Wet curtain cooling is currently more suitable for male and female pig houses, and the cost is relatively low. There are ready-made products on the market for sale. 5, air conditioning cooling. Air-conditioning cooling is to install air-conditioner in a pig house, which can not only reduce the temperature, but also control the humidity. It is the best cooling measure at present, which is the cost is too high. However, I believe that it is worthwhile to implement centralized management and installation of air conditioning for boars and production sites that use artificial insemination technology. Can significantly improve the quality of semen in summer boars. (B) adjust feed nutrition, strengthen feeding management: 1, adjust the feed formula: (1) under high temperature conditions, pigs in order to reduce body heat, reduce heat dissipation, is bound to reduce feed intake, resulting in pig energy, protein and other nutrients Inadequate intake may affect pig growth and development. Making necessary adjustments to feed formulations has become one of the effective measures to overcome heat stress. As the body heat of nutrients increases, the heat burden on pigs increases and the heat stress becomes more severe. Therefore, raw materials with good palatability, fresh and high quality are used in combination with diets, and the proportion of high-fiber raw materials is properly reduced to control the diets. Crude fiber levels to reduce body heat production. Carbohydrates and fats are the main source of energy for pigs, but the body heat of carbohydrates is greater than that of fats. Therefore, the carbohydrate content of feeds should be appropriately reduced. Small grease volume, high net energy value, and low body heat increase are ideal sources of energy for pigs under high temperature conditions. They can add less than 5% fat to feed. Under the condition of heat stress, the requirement of protein for pigs increases. Therefore, increasing the crude protein content in feed can increase the feed utilization rate and reduce the heat-dissipation burden of pigs during the hot season (there are also reports that balancing amino acids and reducing crude protein intake are alleviating pigs. Important measures of heat stress). (2) Add 200--500 mg/kg vitamin C and 200 mg/kg vitamin E to the feed to increase pig immunity, increase heat stress resistance, and increase feed intake and daily gain. (3) The appropriate amount of sodium bicarbonate (250 mg/kg) and trace element potassium can also alleviate the adverse effects of heat stress on pigs. (4) Feeding a certain amount of green feed daily for male and female sows during the summer can increase the appetite and anti-stress ability of the herd. 2. Strengthen management: Reduce the housing density of the pig house and reduce the temperature in the pig house. Regularly check the amount of water discharged from the automated drinking fountains to ensure that the pigs are supplied with sufficient water to promote body heat loss. Changing dry feeds to wet feeds or pelleted feeds can increase pig feed intake. Adjust the feeding time and increase the number of feedings. Feed in advance in the morning and feed in the afternoon, try to avoid feeding when the weather is hot, and feed 1 at night. Do a good job of keeping the feed and prevent mildew. In order to increase sow fertility, avoid breeding in the hot season and use the method of estrus in the same period to make most sows concentrate in the season when the temperature is more suitable. (c) Add anti-heat stress drugs. 1. In a high-temperature environment, adding sucrose, electrolytes (oral rehydration salts, etc.) to drinking water can significantly promote piglet growth and increase feed remuneration. 2, when the temperature exceeds 34 degrees, it is appropriate to try vitamin C, vitamin E, biotin and choline and other anti-heat stress drugs. 3. Adding 10 mg/kg of daidzein or 400 mg/kg of taurine to feed can also reduce the impact of heat stress on finishing pigs. Adding 300 micrograms/kg chromium (chromium pyridine carboxylate) to pig feed kept in a hot environment can relieve high temperature stress, increase feed intake and daily weight gain, and reduce feed-to-weight ratio. It takes some time for chromium to work (after 2 weeks). 4. Chinese herbal medicine can fully coordinate the physiological metabolism of pigs under high temperature, promote pig growth and development, and improve the body's immune function. Adding a certain proportion of pig prohormone (Chinese herbal medicine preparation) to the diet of weaned piglets in a hot environment has a good effect of promoting growth, and can reduce the ratio of feed to feed and material cost. The Chinese herbal medicines Hawthorn, Atractylodes Rhizome, Citrus, Betel nut, Astragalus membranaceus, Daqu, etc., which are used for appetizing spleen and refreshing heat to relieve summer heat, are used as feed additives to ease the impact of hot environment on commercial pigs and increase weight gain and feed utilization. The Chinese herbal medicine, vitamins, minerals, electrolytes, etc. are formulated into additives in a certain proportion, which can harmonize the regulation function of the pig body, enhance the pig's adaptability and ability to resist high temperature, thereby alleviating the pig's heat stress. There are also related products on the market.

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