Detailed Explanation of the Harm, Clinical Manifestations and Prevention and Treatment Methods of Heat Stress in Chickens
(1) Heat tolerance of chickens. Because chickens have physiological characteristics such as high body temperature, vigorous metabolism and no sweat glands, their ability to tolerate high-temperature environments is low, so high temperature becomes the most harmful stress factor among chicken stressors. According to relevant measurements, for laying hens raised in China, the optimal digestion temperature is 21-24°C, the optimal laying temperature is 15-20°C, and the relative humidity is 60%-65%. When above 28°C, egg production declines, and for each 1°C rise, heat dissipation decreases and feed intake drops by 1.6%; at around 30°C it drops by 3%-4%, and panting appears. The physiological regulation of temperature in chickens can reach 32°C. At 35°C, physiological regulation is inhibited, and symptoms such as elevated body temperature, severe heat panting and fainting appear, and even death occurs.
(2) Heat stress monitoring in chickens. China currently has no monitoring standards, but from the perspective of the physiological and biochemical effects of high temperature on chickens, there are the following aspects.
1. Clinical manifestations. Reduced feed intake or refusal to eat, increased drinking water, heat panting, mental tension or depression, decreased egg production, small and dry feces with blood, cyanosis of the comb (sometimes pallor), and other phenomena.
2. Blood changes. Blood glucose, blood lipids and total protein decrease significantly. The partial pressure of oxygen is decreasing, and the partial pressure of carbon dioxide is rising. Blood potassium decreases, and blood sodium increases. The activity of ML phosphokinase in serum rises sharply, the activities of alanine aminotransferase and lactate dehydrogenase decrease significantly, and vitamin C decreases. Plasma aldosterone increases, and is consistent with changes in serum potassium and sodium. Estradiol, corticosterone and thyroid hormone decrease.
3. Necropsy. Muscles are pale, soft as mud, and show cooked-like changes; the myocardium is dilated with large petechial hemorrhages; catarrhal enteritis; the cloacal mucosa shows changes such as congestion, hemorrhage and edema.
(3) Prevention and treatment of heat stress. When the air temperature exceeds 32°C and is below 35°C, it has a great impact on production, and when the air temperature exceeds 35°C, individual chickens will die. Therefore, different countermeasures should be taken according to different temperatures inside the house.
1. When the air temperature inside the house reaches 30-35°C, 0.2% sodium bicarbonate should be added to the feed, or 150-300 grams of vitamin C should be added per ton of feed. If the amount of sodium bicarbonate is increased, the amount of sodium chloride in the feed should be reduced accordingly. Because the temperature is high, the vitamin requirements of chickens are generally more than 2 times normal, so supplementing sufficient vitamins is particularly important in summer.
2. When the air temperature inside the house is higher than 35°C, chicken deaths will occur in the flock, and the higher the temperature, the more severe the chicken deaths. For prevention and treatment, use 10 grams of analgin dissolved in 50 kg of water and let them drink it all day, with excellent results.