The characteristics of heat stress
Heat stress in laying hens occurs in henhouses with a temperature exceeding 32°C, poor ventilation, and poor sanitary conditions. The severity of heat stress increases with the increase in the temperature. When the temperature exceeds 39°C, it can quickly lead to heat stress in laying hens and result in the death of large numbers of chickens.
Breeders, especially broiler breeders, are less tolerant to heat stress. When heat stress occurs, it seems that the chickens that are physically strong and physically obese are the first to die. This situation is also very likely to occur in high-yielding chickens.
The peak of death of heat-stressed chickens is between 7 pm and 9 pm, and the temperature in the summer from 10 am to 5 pm in the summer continues to increase, especially for chickens that are sensitive to heat stress. 5 pm to 6 pm At this point, the body temperature regulation function has reached its limit. At this time, the body temperature has risen to the critical temperature of heat shock (45.3°C). If no immediate measures are taken to quickly disengage the chicken from the thermal environment, most of the layers will be at night 7 Point to 9 o'clock shock death.
Clinical symptoms and necropsy changes
Clinical symptoms
Affected chickens generally exhibit elevated body temperatures, mouth breathing, wings open, prone movement, drastically increased drinking water, markedly reduced feed intake, severe food waste, thin watery stool samples, decreased egg production, and reduced egg weight. The contents of eggs are thin, and the percentage of soft-shelled eggs is significantly increased. The fertilization rate and hatching rate of breeding eggs are also greatly reduced. Chickens and broilers showed poor growth and development, and the yield and evenness were reduced. If the duration of heat stress is long, the physiological function of the chicken body will be disordered due to the occurrence of "Heat Stress Syndrome" in the later period, and it will die if it fails.
Necropsy changes
The hernia sac is often full of contents; the lungs are congested or stagnated, and in severe cases, they are purple-black and some of the lung tissue is necrotic; the glandular and gastric mucous membranes fall off and the glandular stomach wall becomes thinner; most of the intestinal mucosa is detached or easily detached, and the intestinal wall becomes thin. In the duodenum and jejunum, the performance is particularly evident. There are a lot of watery contents in the intestine; the lungs and ovaries are congested, and some hens still have eggs to be produced.
Prevention
Create a suitable environment
Sunlight is an important factor in the increase in temperature. To reduce the intrusion of heat of irradiation:
(1) A 2 cm thick white foam plastic can be used as a ceiling at the top of the house, and a large amount of hot air can be placed on the ceiling to reduce the temperature inside the house by about 2°C.
(2) It is possible to cover the roof of the house with straw or wheat straw of 10 cm to 15 cm thick, sprinkle with cold water, and keep it moist for a long time, which can prevent a large amount of heat from being sucked into the house.
(3) You can put a awning on the window to block direct sunlight into the house. In addition, it is necessary to do a good job of greening outside the house so that it can absorb heat and reduce air temperature through the photosynthesis of plants.
Spraying cold water manually to reduce space temperature
After 12 o'clock noon every day, the cold water just sprayed from the well can be sprayed with space by means of a high-pressure sprayer, and the spray can be sprayed once every 2 to 4 hours depending on the temperature in the house. Generally, the temperature in the room can be reduced by 4°C to 7°C. °C. Not only can effectively reduce the thermal stress of laying hens, but also can increase the egg production rate.
Strengthen ventilation and reduce heat inside
Increase the power of the ventilation fan, change the horizontal ventilation to vertical ventilation, increase the speed of the wind flowing through the chicken body, and timely take away the heat generated by the chicken body, so as to achieve the purpose of preventing heatstroke and cooling, such as the combination of spray water spraying, the effect is better.
Using Feed Additives to Reduce Heat Hazard
Add appropriate amounts of vitamin C, vitamin E, vitamin K, vitamin B, and additives such as biotin and bacitracin zinc to the chicken diet; add appropriate baking soda, bromide buffer, Huoxiangzhengqi water, etc. in drinking water , can effectively prevent or reduce the harm of heat stress, improve chicken production performance.
Strengthen feeding management and improve chicken's anti-stress ability
(1) Ensure adequate, clean and cool drinking water. When the temperature is high, the amount of drinking water in the chicken increases, and the excretion of feces is also large, so that more heat can be taken away from the body and the heat stress can be relieved. However, it should be noted that drinking water must be clean, preferably cool deep well water.
(2) To reduce the dietary volume and increase the feed nutrient concentration. High temperatures reduce the appetite of chickens and feed intake decreases. If the proportion of diets such as protein, vitamins, and minerals is not increased, the intake of protein, vitamins, minerals, and other nutrients in chickens will be seriously insufficient, resulting in Reduced production performance. Therefore, dietary nutrient concentrations should be increased to meet the nutritional needs of chickens based on feed intake.
(3) To choose the appropriate feeding time. The temperature is high at noon in the summer and the appetite of the chicken is low. Therefore, it is best to add ingredients in the morning and evening. At this time, the chicken has a strong sense of hunger, a suitable temperature and a good appetite. It can increase the feed intake, satisfy the nutritional needs of the chicken, and improve the anti-stress. ability.
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