What are the mitigation measures for heat stress in broiler chicken farming?
Pay attention to drinking water management. The drinking water intake of chickens under heat stress is an extremely important factor. Under heat stress, more than 80% of the heat produced by chickens is dissipated through evaporation. Studies have proven that an increase in drinking water intake is beneficial to the survival of chickens.
Increasing the intake of water containing sodium chloride or lowering the water temperature can both reduce the effects of heat stress. The complementary effect between adding salt to drinking water and the temperature of the drinking water is obvious. When the temperature of the drinking water is lower than the body temperature of the chickens, adding sodium chloride to the drinking water can significantly increase drinking water intake and growth rate; when the water temperature is close to the body temperature of the chickens, adding sodium chloride to the drinking water has little effect on the chickens. Lowering the water temperature without adding sodium chloride can also increase the drinking water intake of chickens; if sodium chloride is added while lowering the water temperature, it has an additive effect on reducing heat stress in broiler chickens.
Reduce flock density. Before midsummer arrives, depending on the rearing method, a thinning of the flock can be carried out in combination with transfer, merging, and culling, and an appropriate number of chickens per cage and rearing density should be arranged. Floor-reared flocks should not be too large, and activities such as transfer, beak trimming, and transport should be avoided as much as possible. If they must be carried out, they should be done on cloudy days or in the cool morning and evening weather.
Increase ventilation inside the house and reduce solar radiation. In the construction of chicken houses, materials with good insulation performance should be considered. Fiberboard can be used to suspend a ceiling, walls can be painted white, and trees and lawns can be planted around the chicken house. These measures help reduce radiant heat from the outside entering the chicken house. Modern chicken farms are highly intensive, and doing a good job of ventilation and cooling inside the house is an important part of preventing heat stress in broiler chickens. The simplest method is to install fans in the chicken house. When the ambient temperature is below 40°C, increasing wind speed helps dissipate body heat from the chickens. In recent years, tunnel ventilation has become an effective means of reducing heat stress, maintaining fresh air inside the house through continuous air exchange. However, when the temperature reaches above 30°C, tunnel ventilation alone can no longer control heat stress, and a wet curtain cooling device must be added to effectively reduce heat stress. Recently, it has become common to install water curtains at the air inlet as humidifiers. In addition, using sprinkling water or spray atomization devices on the roof of the chicken house can increase evaporative heat loss from the roof and ease the transfer of heat from the roof into the house.
Reasonably adjust the nutritional level. (1) Dietary protein and amino acid content: reducing the dietary protein content while maintaining the added level of essential amino acids can improve the growth rate and survival rate of broiler chickens. Corn-soybean-based diets require the addition of methionine to achieve better broiler performance. (2) Adjustment of energy concentration: the adjustment of energy concentration in the diet should be based on the principle of minimizing heat increment. Fat is the nutrient with the lowest heat increment. Appropriately adjusting the proportion of essential fatty acids in the feed and using fat to replace part of the carbohydrates to increase the energy concentration of the feed improves the adaptability of broiler chickens during heat stress. (3) Mineral addition amounts: during heat stress, the urinary excretion of potassium, sodium, zinc, and molybdenum increases, the fecal excretion of calcium, manganese, selenium, and copper also increases, and the storage of magnesium and phosphorus decreases. Timely supplementation according to need can meet the body's requirements.
Application of anti-stress additives. (1) Add vitamin C: supplementing vitamin C during stress can obviously inhibit the rise in body temperature, increase feed intake, and reduce the adverse effects of heat stress on metabolism. Vitamin C can be supplemented through feed or drinking water. (2) Add vitamin E: adding an appropriate amount of vitamin E to the diet of hens suffering from chronic heat stress for 1 week can obviously inhibit the decline in egg production during stress and help egg production return to normal as soon as possible after stress. (3) Add electrolytes: under heat stress conditions, broiler chickens are prone to respiratory alkalosis and hypokalemia, causing electrolyte balance disorders and affecting the body's regulatory activities. Adding electrolytes to drinking water or feed can alleviate the harm caused by heat stress.